HYDROPONICGARDENING

STEVEN CARRUTHERS

• Build your own hydroponic system• Hydroponic techniques• Hydroponic media

• Nutrient management• Plant nutrition• Pests and diseases

HYDROPONICGARDENING

STEVEN CARRUTHERS

After your first harvest you will delight in howsimple hydroponic gardening is, and hownutritious, flavoursome and fragranthydroponically grown vegetables, fruit andflowers can be!

Hydroponics for the home gardener is an economical and simple way to turn your backyard, nomatter how big or small, or balcony into productive vegetable, herb and flower gardens.

Hydroponic Gardening, designed for beginners of all ages, teaches the basics of hydroponicgardening—how to grow hydroponic plants from seed, and to feed them with naturallybalanced nutrients. It also shows you how to transplant plants from soil to hydroponics andhow to take clones from valuable plant stock for hydroponic cultivation.

Once your hydroponic garden is established, learn all about:

• the fundamental principles of nutrient management and nutrition• how to recognise and remedy nutritional disorders• how to combat pests and diseases the natural way• how to maintain an ecological balance in your hydroponic garden.

Foreword 4

Introduction 7

Plant nutrition 10

Basic elements; Nutrient solutions; Nutrient management;

Nutrient guide

Hydroponic mediums and techniques 22

Water culture; Aggregate culture; Rockwool culture;

Sawdust culture; Aeroponics

Choosing a system 36

NFT system; Flood-and-drain system; Drip-irrigation system;

Aeroponic system; Other systems

Building a system 44

NFT system; Flood-and-drain system; Drip-irrigation system;

Rockwool system; Aeroponic system; Electrical pumps; Filters

Planting 52

Seed germination; Cloning; Transplanting from soil; Nutrient solutions;

Temperature; Water; Oxygen; Light; Plant spacing; Plant support

Nutritional and environmental disorders 58

Remedial action

Managing diseases and pests 64

Disease control; Disease prevention; Pest control; Algae control

Maintaining your system 76

Maximising your growth; keeping records

Common questions about hydroponics 80

Further reading 83

Hydroponics might be seen by some as a fad, or a novelty tobe pursued by those with plenty of time and space. Far fromit, as Steven Carruthers shows in this book, hydroponics is nota recent gimmick but an age-old approach to plant cultivation.It can also be an efficient way of growing plants as you mayhave fewer problems with pests and disease and plant growthmay be speedier because the plants receive a constant supplyof nutrients that they can readily use.

Not all of us will want to convert our back garden to thecultivation of plants by hydroponics, but we may enjoyexperimenting with some of the smaller systems available. Andthose with balconies rather than backyards may findhydroponics the simplest and most effective way to grow a fewherbs, vegetables or flowers. The use of hydroponic plantersystems also allows effective, continuous supply of waterduring the heat of our summers, a time when plants incontainers are easily stressed.

Whether you seek an ambitious hydroponics scheme orsimply an answer to growing a few pots on your balcony, thisbook should help you by providing practical advice andanswers to your questions, easy or difficult, to extend yoursuccess as a hydroponic gardener.

JOHN PATRICKEditor-Lothian Gardening Series

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Casper Publications Pty LtdPO Box 225Narrabeen, NSW 2101Ph: +612 9905-9933Email: info@hydroponics.com.auWebsite: www.hydroponics.com.au

Copyright Steven Carruthers, 1951

First published 1993Reprinted 1994, 1996, 1997, 1998, 2000,2002, 2004Revised 2015

All rights reserved. No part of thispublication may be reproduced, storedin a retrieval system or transmitted inany form by any process without theprior permission of the copyrightowner. Enquiries should be made to thepublisher.

National Library of AustraliaCataloguing-in-publication data:Carruthers, Steven L., 1951 -Hydroponic Gardening

ISBN 978-0-9775063-5-4 (eBook)

Foreword Contents

Hydroponics is defined as growing plants in systemsisolated from the soil, either with or without a growingmedium, and fed with the total water and nutrients the

plants require. The term comes from the Greek words ‘hydro’ forwater and ‘ponos’ for labour. It is sometimes referred to as ‘soillessculture’ and ‘hydroculture’.

The science of hydroponics is not a new concept in growingplants; it has been around for centuries. The earliest recordedreferences date back to the Hanging Gardens of Babylon, built byKing Sennacherib at Nineveh, near the modern-day Iraqi city ofMosul. Sennacherib was king of a large Assyrian empire with hiscapital at the ancient city of Nineveh, more than 400 km (250 miles)north of Babylon. He reigned between 705 and 681 BC. Cuneiforminscribed prisms from the palace foundations contain detailedreferences to a wonderful garden including terraces, water canalsand large trees above arches, an engineering masterpiece for anyage. Part of the arches still survive today.

The legendary Hanging Gardens of Babylon was listed as oneof the Seven Wonders of the (ancient) World. In Greek texts, thestory is that the gardens were built by an Assyrian king for hisqueen, the daughter of the king of the Medes, to create an alliancebetween the nations. The land she came from was green, rugged andmountainous in contrast to the flat, sunbaked landscape aroundBabylon. The king decided to make her feel more at home bybuilding a small mountain with rooftop gardens. Archeologicaldiscoveries in the early 1800s point to Sennacherib as the Assyrianking who built the fabled gardens. A bas-relief carved panel in theBritish Museum show an elevated garden, which was taken fromNineveh. The details show terraces and large trees above arches.They also show water channels. This evidence was ignored untilrecently, because the hanging gardens were said to be in Babylon,according to Greek texts, not Nineveh.

There were a number of canals supplying water to Nineveh,but by far the most impressive was the 95 km (60 mile) canal builtby Sennacherib. This took water from Khinis, on the edge of theAmanus Mountains to Nineveh. It had a fall of only one metre perkilometre, uniform over its entire circuitous length. Part-way along

Introduction

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Sennacherib (704–681 BC) succeeded hisfather Sargon II on the throne of Assyria.

Nineveh—Sennacherib palace archealogy site,near the present-day city of Mosul, Iraq.

Typical chinampas construction showingthe built-up level of the beds, plus the

trees used to prevent erosion. The canalswere used for transport and were wide

enough for two boats to pass.

its route it needed to cross another river at Jerwan, so he had anaqueduct built. It consisted of over two million large dressedlimestone blocks, average size about a 50 cm (20 inches) cube and,hence, weighing over 300 kg (700lb) each. Much of the aqueductremains in place today. Interestingly, their shape is the same as thoseon the bas-relief of the Hanging Gardens.

This was an engineering masterpiece for any age, let alone2600 years ago and 500 years before the Romans built theiraqueducts. The planning and building of the canal and aqueductclearly shows that Sennacherib and his engineers had the skillsneeded to build hanging (elevated) gardens. The canal would alsohave provided the extra water needed to irrigate the gardens.

Was this hydroponics? The Hanging Gardens can not beconsidered to be strictly hydroponics as they were soil-based.However, they did use the technique of having soil as a growingmedium in containers separated from the general soil. They alsoused relatively sophisticated irrigation techniques. Both of theseindicate that this is an admirable predecessor of hydroponics, andworth its place in the history of hydroponics.

The principles of hydroponics can also be found in the floatinggardens of Kashmir, in the shallows of Dal Lake at the foot of theHimalayas. These man-made floating gardens have been around formore than 500 years. Today, the majority of people living on thesegardens are Shia Muslims. The material used for the floating gardensare the rootstocks of emergent water plants common in shallowparts of the lake. The naturally buoyant roots are detached from themud and covered with layers of sediment and decaying plantsbefore vegetable cultivation is started. By raising beds above thewater level, these crops enjoy constant irrigation and produce hugeharvests, although you need a boat to reach them. In modern timesthe floating gardens have virtually choked the lake.

The Aztec Indians also grew plants on floating rafts in shallowlakes as far back as the ninth century. Known as ‘chinampas’, theywere first set up by tribes living beside islands on lakes Chalco andXochimilco, part of a series of five shallow interconnected lakes whichare now mostly covered by Mexico City. Chinampas were long,narrow rectangular beds built in marshy or shallow water andsurrounded on three or four sides by canals. The canal size varied butcould get as big as about 10 metres (30 feet) wide and up to 100 metres(300 feet) long. The floating rafts were made of reeds covered withlayers of mud and aquatic plants to create a compost bed. A few ofthese rafts can still be found today on the lakes near Mexico City.

Today, many of the different methods of hydroponic

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gardening come from the ideas of Dr William F. Gericke, a plantprofessor at the University of California. Gericke became famouswhen he produced tomato plants 7.6 metres (25 feet) tall through hismethod of soilless gardening. He was the first to name the scienceof soilless culture ‘hydroponics’.

One of the early successes of hydroponics occurred on WakeIsland, a rocky atoll in the Pacific Ocean used as a refueling stop forPan American Airlines in the 1930’s. Hydroponics was used thereto grow vegetables for the passengers because there was no soil, andit was prohibitively expensive to airlift in fresh vegetables.

During the Second World War both the American Army andBritish Royal Air Force established special hydroponic farms to growmillions of tons of fresh vegetables to feed allied soldiers and airmen.The shipping of fresh vegetables to overseas outposts was notpossible owing to the unavailability of refrigerated transport. Duringthis period hydroponic techniques were given their first real test asa viable alternative for the commercial production of freshvegetables. One of the first hydroponic farms was built on AscensionIsland, a barren island in the South Atlantic, and an importantstaging base for the US Air Force. The hydroponic techniquesdeveloped on Ascension were later used on the various islands inthe Pacific, including the Aleutian Islands off Alaska, Wake Island,Iwo Jima and Okinawa. They were also used to feed the occupationforces in Japan after the war and Allied servicemen serving in Koreaduring that conflict. The most notable of these hydroponic farms wasCamp Cofu, located on the outskirts of Tokyo. Over its 15-yearoperational life, Camp Cofu produced nearly 10 million kilogramsof fresh vegetables, reaching its peak in 1954 with the production ofnearly 6 million kilograms of produce.

Today, hydroponics plays an important role in the world’sagricultural development. Climate change, population pressures,scarce and inequitable water distribution, and polluted ground waterare all factors influencing alternative horticultural methods. Since itsmodern-day revival, hydroponics is being adapted to many situations,from commercial greenhouse production to specialised applicationsin Antarctica to provide fresh vegetables for research teams. It is aspace-age science, but at the same time it is being used in developingcountries for food production. Its only restraints are sources of freshwater and nutrients. In areas where fresh water is not available,hydroponics can use seawater that has been desalinated.

In Australia, where climate conditions are harsh andunpredictable and arable land is limited, hydroponics is used tomeet urban market demands for fresh produce and fresh cut flowers

Advantages of hydroponics• Higher yields compared to soilgardening

• More efficient use of water andfertilisers

• Water and nutrients are recyclable• Plants reach maturity sooner• Better quality produce with longershelf-life

• Denser planting is possible• Suited to non-arable areas• Soil pests and diseases are reduced• Less maintenance because thereare no weeds to remove.

Disadvantages of hydroponics• More skills and knowledge isrequired

• The initial capital costs of setting up a hydroponic garden can behigh. However, simple, low-costhydroponic systems can beimprovised using odds and endswhich can nearly always be foundaround the home

• Plant disease can spread quickly toplants with shared nutrientsolutions, however there is muchless chance of plant diseasecompared to soil gardening

Camp Cofu started soon after WWII togrow fresh food for American servicemenin Korea.

Gericke became famous when heproduced tomato plants 25 feet tallthrough his method of soillessgardening.

for local and export markets, and to grow fodder for livestock. Forthe home gardener, it is an economical and simple way to turnpocket-handkerchief-sized backyards into productive vegetable,herb and flower gardens.

Hydroponics is simply a highly efficient way to provide foodand water to plants. In a soil garden, food and water are randomlydistributed and plants need to expend a lot of energy growing rootsto find them. In a hydroponic garden, the food and water aredelivered directly to plant roots. Plants grow faster and can beharvested sooner because they are putting their energy into growingabove the ground, not under it.

Once established, plants flourish, giving higher-than-averageyields, even on balconies and in small backyard areas. Plants canbe grown closer together than in normal gardens because they donot have to compete with weeds and other plants for water andavailable nutrients.

There are no physiological differences between plants grownhydroponically and those grown in soil. The subsequent process ofmineral and water uptake by the plants is the same for both growingenvironments. The fundamental difference is in the way in whichthe nutrients are delivered to the plants.

In soil the nutrients necessary for healthy growth arecontained in organic matter, and might not be released as and whenrequired by the plant. Soil gardens are fertilised with manures andcomposts made of decayed organic matter; but plants cannot usethis matter until it has broken down into the basic nutrient salts – aslow process. In hydroponics, nutrients are immediately availableto the plants. As a result, flowering and fruiting are achieved muchsooner than in soil.

While hydroponics has been applied commercially inAustralia since the early 1970’s, only recently has it become popularamong home gardeners. Pressures on the size of urban blocks ofland, spiralling vegetable prices and the desire to grow fresh leafygreens, fruits, vegetables and flowers are largely responsible for thisgrowing demand. Consumers are also much more aware of theenvironment they live in. Soil degradation, deforestation, chemicalpesticides and food additives are all of concern, making consumersmore vocal in their demand for safe and environmentally friendlyfresh produce.

While the idea of hydroponic gardening may seem complex,it is no more complicated than traditional gardening methods.Exactly the same horticultural principles apply to both. This book, Ihope, will inform and inspire newcomers to hydroponic gardening.

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trace elements (those needed in considerably smallerquantities).

The macro-elements are carbon (C), hydrogen (H),oxygen (O), nitrogen (N), phosphorus (P), potassium (K),calcium (Ca), magnesium (Mg) and sulphur (S). The micro-elements are iron (Fe), chlorine (Cl), boron (B), manganese(Mn), copper (Cu), zinc (Zn) and molybdenum (Mo).

Essential elements and what they do

Macro-elementsCarbon (C) is a constituent found in all organic compounds.Hydrogen (H) is a constituent of all organic compounds ofwhich carbon is a constituent. It is important for the cationexchange in plant-medium relations.Oxygen (O) is a constituent of many organic compounds. It isessential in the anion exchange between roots and the externalmedium.Nitrogen (N) is used in various forms to promote rapidvegetative growth, leaf, flower, fruit and seed development,anc chlorophyll development; and to increase the proteincontent in all plants.Phosphorus (P) promotes and stimulates early growth andblooming and root growth. It hastens maturity and seedgrowth, and it contributes to the general hardiness of plants.Potassium (K) promotes disease resistance and gooddevelopment of carbohydrates, starches and sugars, and itincreases fruit production.Calcium (Ca) is vital in all parts of plants to promote thetranslocation of carbohydrates, healthy cell wall structure,strong stems, membrane maintenance and root structuredevelopment. It sometimes interferes with the ability ofmagnesium to activate enzymes.Magnesium (Mg) promotes the absorption and translocationof phosphorous. It activates many enzymes and it appears toaid in the formation of oils and fats. It also plays a role incarbon dioxide assimilation.Sulphur (S) promotes the synthesis of oils, good cell wallstructure, and the synthesis and function of protein.

Micro-elementsIron (Fe) acts as a catalyst in the photosynthesis andrespiration process, and it is essential for the formation of

General ruleAs a general rule plants have ahigher nutrient requirement duringcooler months and a lowerrequirement in the warmer months.A stronger nutrient solution shouldtherefore be maintained duringwinter and a weaker solution insummer when plants take up andtranspire more water than nutrient.

Modern-day hydroponics has evolved from earlystudies of plant constituents, which led to thediscovery of essential plant elements. Plant nutrition

is therefore the basis of hydroponics. Anyone intending to adoptsoilless culture techniques should have a good knowledge of thissubject, as management of plant nutrition through managementof the nutrient solution is the key to success in hydroponicgardening.The hydroponic method enables gardeners to control availablenutrients. In conventional gardening, once fertilisers or nutrientsare added to soil there is no easy way to change or reduce theirconcentrations. By contrast, in hydroponics the nutrient solutioncan be adjusted or changed to suit the particular stage of plantgrowth. Also, not needing to search or compete for availablenutrients as they do in soil, the plants reach maturity muchsooner because the nutrients provided are already balanced andready to use. In simple terms, optimisation of plant nutrition ismore easily achieved in hydroponics than in soil.

Basic elementsWhile ninety-two natural mineral elements are known to exist,only sixty of these have been found in plants. Of these, onlysixteen are considered essential for plant growth. To beconsidered essential for healthy plant growth, an element mustfulfil four criteria:

• It must be necessary for the plant to compete its life cycle.• Its action must be specific (that is, not wholly replaceable

by any other element).• It must be directly involved in the nutrition of the plant (that

is, required for the action of an essential enzyme).• It must not antagonise a toxic effect of another element.

The sixteen elements that are generally considered essentialfor plant growth are divided into macro-elements (those that arerequired in relatively large quantities) and micr0-elements or

Plant Nutrition

ElementsElements are listed in severalgroups or classifications,depending upon the amountnormally used by plants in theirgrowth and development.

Macro-ElementsNitrogen (N)Phosphorus (P)Potassium (K)

Secondary macro-elementsCalcium (Ca)Magnesium (Mg)Sulphur (S)

Micro-elementsIron (Fe)Boron (Bo)Zinc (Zn)Copper (Cu)Manganese (Mn)Molybdenum (Mo)Chlorine (Cl)

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presence of sludge in pre-packed liquid nutrients, or lack ofsolubility when powdered formulations are mixed with water,is an indication of poor-grade nutrient salts. The sludgecontains inert carriers, such as clay, silt and sand particles,which do not supply ions. Such impurities can block theavailability of other nutrients to plant roots, as well as blockfeeder lines.

Most nutrient solutions available on the market containall the essential elements for plant growth, and are classified asgeneral purpose solutions. The best of these are consideredsuitable for almost any system. Some nutrient solutions may bespecifically tailored for rockwool, which is more alkaline thanother mediums and so requires a different nutrient profile.

Nutrient formulations are available in either powder orliquid form. While each has its followers, liquid nutrient ismore popular among home gardeners because of itsconsistency and its easy and convenient mixing instructions.

Nutrient is also available in a ‘grow’ and a ‘bloom’formulation so that plants can utilise different elements atdifferent stages of their growing cycles. In the early stages theyneed more nitrogen for the production of leaves, shoots andstems. This is called the ‘vegetative’ stage of growth. As plantsmature, they begin to set buds, a sign that they are entering areproductive phase. At this time plants will begin to use lessnitrogen and more potassium and phosphorus, the elementsassociated with the formation of flowers and fruit. The changefrom a ‘grow’ to a ‘bloom’ formulation helps a plant tomaximise its potential to set flowers and fruit.

Some very good one-part nutrients are also available,which use high quality components known as chelates(pronounced ‘key-lates’). These nutrients are suitable for awide range of plants and systems and are easy to use.

Replacing the solutionIndividual plants absorb elements at varying rates and invarying quantities. As a result, some elements become in shortsupply before others. The exact deficiency of individualelements in the solution used in hydroponics is impossible todetermine without costly laboratory analyses. The onlysafeguard against nutrient disorders is therefore to replace thesolution regularly, ensuring spent solution is discardedresponsibly such as diluting with water and using on soilgardens or lawns.

sugars and starches. Iron also activates certain other enzymes.Chlorine (Cl) is essential for photosynthesis where it acts asan enzyme activator during the production of oxygen fromwater.Boron (B) is essential for cell wall strength and development,cell division, fruit and seed development, sugar transport andhormone development. Some functions of boron inter-relatewith those of nitrogen, potassium, phosphorus and calcium inplants.Manganese (Mn) activates one or more enzymes in fatty acidsynthesis and the enzymes responsible for DNA and RNAformation. It also participates directly in the photosyntheticproduction of oxygen from water and may be involved inchlorophyll formation. Manganese is closely associated withcopper and zinc.Copper (Cu) is an internal catalyst and acts as an electroncarrier. It is also thought to be involved in nitrogen fixation.Zinc (Zn)with copper and manganese is linked to chlorophyllsynthesis. It is also essential for auxin metabolism.Molybdenum (Mo) acts as an electron carrier in the conversionof nitrate to ammonium. It is essential for nitrogen fixation andnitrate reduction.

Nutrient solutionsFor hydroponic applications, all essential elements are suppliedto plants in the form of nutrient solution, which consists offertiliser salts dissolved in water. While many commercialgrowers formulate their own nutrient solution for a particularcrop, the home gardener can choose from a range of good-quality, general purpose hydroponic solutions alreadyformulated and packaged in small containers. They are availablein either liquid or powder form, and single or twin packs.

While it is not necessary in this book to delve deeply intonutrient formulations, it can be fairly stated that these takemuch of the guesswork out of plant nutrition for the homegardener. However, it is important to avoid any pre-packed,concentrated nutrient solution that contains sludge.

Nutrient salts have different solubilities – that is, differentconcentrations of salt that will remain in solution whendissolved with water. If a fertiliser salt has a low solubility,only a small amount will dissolve in water. In hydroponics,fertiliser salts must have high solubilities since they mustremain in solution in order to be available to the plants. The

Single-part Grow and Bloom nutrient(above), and two-part Grow and Bloomnutrients. (below).

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In soil, most plants prefer a pH level on the acidic side ofneutral. Most hydroponically grown plants prefer a slightlymore acidic solution, with the optimum pH being somewherebetween 5.8 and 6.5. For pH values above 7.5, iron, manganese,copper, zinc and boron become less available to plants. If pHfalls below pH 6.0, then the solubility of phosphorus, calciumand manganese drops sharply. While hydroponic crops can begrown successfully at higher and lower levels, the further onedeparts from the recommended range the greater the risks ofnutritional problems.

Whereas the degree of acidity or alkalinity in soil iscontrolled by adding either lime or dolomite, the pH range ofa nutrient solution can be controlled by chemical buffers whenit strays outside the ideal. It can be lowered by adding diluteconcentrations of phosphoric, sulphuric or nitric acid, andraised by adding a dilute concentration of potassiumhydroxide. For convenience, dilute buffer solutions are readilyavailable from hydroponic outlets.

In hydroponics the movement of the pH balance gives agood indication of plant activity. If the pH is rising, or thesolution is becoming more alkaline, then the plant is takingacidic nutrient salts out of the solution. Conversely, if the pHis falling or becoming more acidic, then the plant is taking upalkaline components.

As a general rule, the pH of a nutrient solution should betested daily with a simple water-testing kit or electronic meterand the solution adjusted, if necessary, by using acid oralkaline buffers.

Always perform this check at the same time of day and,if possible, at the same temperature, because the pH of asolution can fluctuate dramatically with light and temperaturevariations during the course of the day. Intense photosyntheticactivity during daylight hours causes the pH to rise, and atdusk, when photosynthesis ceases, intense plant respirationcauses the pH to drop. Adding buffers to even out these short-term changes can put your system on a roller coaster that isharmful to the plants. Although it is important to stay withinthe recommended pH range, it is far more important toprevent large fluctuations.

Many hydroponic texts give the impression that pH is themost critical aspect of hydroponic management, however mostplants will grow reasonably well from pH 5.0 to pH 7.0.

EC (eletcroconductivity)An indicator of the strength of anutrient solution, as measured by anEC meter. This is the preferred termused worldwide. Its most commonunit is milliSiemens per centimetre(mS/cm). Another unit ismicroSiemens per centimetre(uS/cm). A limitation of EC is that itindicates only the total concentrationof a solution and not the individualnutrient components.

Conversion chartmS/cm cF ppm0.5 5 3501.0 10 7001.5 15 10502.0 20 14002.5 25 17503.0 30 21003.5 35 24504.0 40 28004.5 45 31505.0 50 3500

In any hydroponic system where the nutrient solution isrecycled, which is the majority of cases, the life of the solutionis two or three weeks, depending upon the season, the natureof the crop and the stage of plant growth. During the hotsummer months, when plants transpire more, take up morewater and therefore the nutrients concentrate, the solutionmay have to be changed as often as once a week, especially ifplants have reached an advanced stage of growth.

Nutrient managementWhile optimum nutrition is easy to achieve in hydroponics, sois damage to plants due to errors in making up the nutrientsolution and/or failure to adjust it daily. In systems that arecontrolled to any degree by automatic devices, poormaintenance and equipment failure can also damage ordestroy plants.

The success or failure of a hydroponic garden thereforedepends primarily on a strict nutrient managementprogramme, and this is achieved by carefully manipulatingthe pH level, temperature and electroconductivity (EC) of thesolution. This manipulation, combined with a rudimentaryknowledge of both, is the key to successful hydroponicgardening.

pH levelIn simple terms, pH is a measure of acidity or alkalinity on ascale of 1 to 14. If you have had a swimming pool, you may befamiliar with pH, or you may have come across the term inskin and hair care products. For those who have studiedchemistry, it is defined as the cologarithm of the activity ofdissolved hydrogen ions (H+). Hydrogen ion activitycoefficients cannot be measured experimentally, so they arebased on theoretical calculations. The pH scale is not anabsolute scale; it is relative to a set of standard solutions whosepH is established by international agreement.

In a nutrient solution, the pH level determines theavailability of essential plant elements. A solution is deemedto be neutral at pH 7.0, alkaline if above and acidic if below.The pH for pure water at 25°C (77°F) is close to neutral andchanges above or below this represents large changes in thedegree of acidity or alkalinity. For example, a solution pH of6.0 is ten times as acidic as a solution pH of 7.0, and a solutionpH of 5.0 is 100 times as acidic as pH 7.0.

Effects of pHA high pH can reduce theavailability of iron, manganese,boron, copper, zinc and phosphorusto plants. A low pH can reduce theavailability of potassium, sulphur,calcium, magnesium andphosphorus.

Nutrients and lightLow light conditions cause plants totake up more potassium andphosphorus, thereby making thenutrient solution more acidic. This isparticularly evident on overcast days.Conversely, on clear sunny days,plants take up more nitrogen, makingthe nutrient solution more alkaline.

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solutions expressed as either parts per million (ppm), for TDSmeters, or milliSiemens (mS) for EC meters. To convertmilliSiemens to conductivity factors, multiply by 10. Toconvert EC to ppm, multiply by 650. Conversely, to convertppm to EC, divide by 650.

For optimum results, a meter that will measure nutrientstrength is indispensible not only to the commercial growerbut also to the serious home gardener. If a meter is notavailable the nutrient solution should be discarded weekly,and a fresh solution made.

Plant requirementsPlants can be categorised generally as either low, medium orheavy feeders, and require correspondingly low, medium orhigh nutrient strengths. Only plants that fall into one categoryshould be grown together using the same nutrient strength. Todo otherwise will give only one plant type the optimumgrowing conditions, making the others slower to mature.

Any plants grown outside the optimum EC or TDS rangewill result in poor quality fruit and flowers. For example, ahigh-strength solution will make a low feeder, such as lettuce,taste bitter and a low-strength nutrient solution will makemedium feeders, such as strawberries, and high feeders suchas tomatoes, tasteless, soft and squashy.

During the early development of hydroponics inAustralia, when there was less data available on plantnutrition, hydroponically grown fruit and vegetables earneda poor reputation for being tasteless. Today, hydroponicproduce is full of flavour. Should your produce lack taste andvigour, you can safely assume that it has been grown outsidethe optimum nutrient range. For optimum EC or TDS rangesfor various plants, consult the Nutrient Guide on page 19.

Organic and inorganic solutionsHydroponics and organics may seem to be odd bedfellows. Inthe past, devotees of each have tended to regard one anotherwith a certain degree of suspicion, believing that theirrespective practices were somehow opposed. But there iscommon ground and this is proving to be an area of greatinterest to many new and prospective hydroponic growers.Organic products are natural or are made from a combinationof natural products.

For gardeners who are detractors from inorganic

TemperatureTemperature fluctuations in a hydroponic solution can affect notonly the pH but also the solubility of nutrients. Studies haveshown that the ideal water temperature for total solubility isbetween 20°C and 22°C. Outside this ideal temperature rangetrace elements start to become less insoluble and plant growthand yields may be affected. Temperatures higher or lower thanthe ideal affect plants in the same way as extremes of pH, butgenerally, most plants will grow reasonably well between 18-28°C

ElectroconductivityDuring growth, plants take up the elements they require, therebyaltering the balance of the remaining nutrient solution from dayto day. This feeding process is termed electroconductivity. Todetermine the general extent of nutrient uptake, the remainingsolution should be tested daily and adjusted if required.

If high concentrations of nutrients are revealed, this is anindication that the plants are taking up water faster than they aretaking up essential elements. It follows that, as water is removedby plants, the volume of the solution decreases, with asubsequent increase in nutrient strength, which may harm theplants. In this situation, fresh water should be added to thenutrient solution until the optimum concentration level isreached.

Conversely, for lower-than-normal nutrient concentrations,plants are taking up more nutrients than water and the solutionneeds to be adjusted with additional nutrients.

There are several simple and inexpensive electronicmeters which allow the home gardener to measure easily andquickly the elctroconductivity (EC) or the total dissolved salts(TDS) or conductivity factor (cF), as it is also known. Theseinstruments use a variety of scales, with the strength of nutrient

A sample of water should be taken dailyand tested for pH andelectroconductivity. Not all plantsshare the same electroconductivity andtherfore plants should be growntogether according to their meannutrient requirement. Plants willtolerate a wide pH range and generally,if the electroconductivity is right, thepH will follow.

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Nutrient Guide

VEGETABLES pH EC ppm ClassArtichoke 6.5-7.5 0.8-1.8 520-1170 LAsparagus 6.0-6.8 1.4-1.8 910-1170 LBean (common) 6.0-6.5 2.0-4.0 1300-2600 HBean (Broad) 6.0-6.5 1.8-2.2 1170-1430 MBeetroot 6.0-6.5 1.8-5.0 1260-3500 HBroccoli 6.0-6.8 2.8-3.6 1820-2340 HBrussel sprout 6.5-7.0 2.6-3.2 1690-2080 HCabbage 6.5-7.0 2.6-3.2 1690-2080 HCapsicum 6.0-6.5 1.8-2.2 1170-1430 MCarrot 6.0-6.3 1.6-2.0 1040-1300 MCauliflower 6.5-7.0 1.6-2.0 1040-1300 MCelery 6.5-7.0 1.8-2.4 1170-1560 MCucumber 5.5-6.0 1.0-2.6 650-1690 MEggplant 5.8-6.2 2.4-3.6 1560-2340 HEndive 5.5-6.0 8-1.6 520-1040 LFodder 6.0-6.5 1.0-1.8 650-1170 MLeek 6.5-7.0 2.0-3.2 1300-2080 HLettuce 6.0-6.5 0.8-1.2 520-780 LMarrow 5.6-6.0 2.0-2.6 1300-1690 MOkra 6.0-6.5 2.0-2.8 1300--1820 MOnion 6.0-7.0 1.4-1.8 910-1170 LPak choi 6.5-7.0 1.4-2.0 910-1300 MParsnip 6.0-6.5 1.8-2.0 1170-1300 MPea 6.0-7.0 0.8-1.8 520-1170 LPepino 6.0-6.5 2.0-5.0 1300-3250 HPotato 5.0-6.0 2.0-2.6 1300-1690 MPumpkin 5.5-7.5 1.8-2.6 1170-1690 MRadish 6.0-7.0 1.4-1.8 910-1170 MSpinach 6.0-7.0 1.4-1.8 910-1170 MSilverbeet 6.0-7.0 1.4-1.8 910-1170 MSquash 6.0-6.5 1.2-1.6 780-1040 MSweet Corn 6.0-6.5 1.6-2.6 1040-1690 MSweet Potato 5.5-6.0 2.0-2.6 1300-1690 MTat soi 6.0-6.5 0.8-1.2 520-780 LTomato (large) 5.5-6.5 2.4-3.6 1560-2340 HTomato (small) 5.5-6.5 2.0-2.6 1300-1690 MTurnip 6.0-6.5 1.8-2.4 1170-1560 MUng tso 6.0-6.5 1.6-1.8 1040-1170 MWitlof 6.5-6.7 2.0-2.4 1300-1560 MZucchini 6.0-6.5 1.2-1.6 780-1040 M

Spring onions grown in Perlite.

Fancy lettuce grown in NFT

A general ruleAs a general rule plants have ahigher nutrient requirement duringcooler months and a lowerrequirement in the warmer months.A stronger nutrient solution shouldtherefore be maintained duringwinter and a weaker solution insummer when plants take up andtranspire more water than nutrient.

formulations, there are many organic nutrients specificallydesigned for hydroponics. Among the more popular areformulations containing earthworm castings, seabird and batguano, and sea kelp. These nutrients are widely available inpowdered, granulated or water soluble form, and giveexcellent results when used alone or as additives to inorganicfertilisers. When using organic products for growing plants,the grower is trying to work with nature, not against it. Also,organic formulations are known to build the immune systemof plants, helping to guard against pests and diseases.

However, it’s worth remembering that the quality andyields of hydroponic fruits and vegetables are far higher thanorganic and conventionally grown produce, they have thesame nutritional value as any other, and they are perfectlyhealthy. The fertilisers come from the ground and are refinedto make them available for plant uptake. Relatively smallquantities of inorganic fertilisers are required and transportand application costs are low. It also means inorganicfertilisers can be formulated to apply the appropriate ratio ofnutrients to meet plant growth and fruiting requirements. Bycomparison, organic fertilisers (animal waste and plantresidues) are relatively inefficient because they contain lowconcentrations of nutrients and large volumes of materialneeds to be transported and spread over fields to overcomedeficiencies for traditional organic farming . Also, organicfertilisers take time to break down into the inorganic formsneeded to become available to plants.

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FLOWERS pH EC ppm ClassAfrican Violet 6.0-7.0 1.2-1.6 780-1040 LAloe 5.5-6.5 2.0-2.4 1300-1560 MAnthurium 5.0-6.0 2.0-2.6 1300-1690 MAster 6.0-6.5 1.8-2.6 1170-1690 MBegonia 6.0-6.5 1.4-1.8 700-900 LBromeliad 5.0-7.5 0.8-1.0 520-650 LCacti 6.0-6.5 1.2-1.8 780-1170 LCaladium 6.0-7.5 1.6-2.0 1040-1300 LCarnation 6.0-6.5 1.0-1.2 650-780 LChrysanthemum 6.0-6.5 1.8-2.4 1170-1560 MCitronella 5.5-6.5 2.0-2.4 1300-1560 MCyclamen 5.5-6.5 2.0-2.4 1300-1560 MCymbidium 5.5-6.0 0.6-0.8 390-520 LDahlia 6.0-7.0 1.4-2.0 700-1300 LDieffenbachia 5.0-6.0 1.8-2.4 1170-1560 MDracaena 5.0-6.0 1.8-2.4 1170-1560 MFerns 6.0-6.5 1.6-2.0 1040-1300 LFicus 5.5-6.0 2.0-2.6 1300-1690 MFreesia 6.5-7.2 1.0-2.0 650-1300 LGypsophila 5.0-6.5 1.6-2.0 1040-1300 MGeranium 6.0-6.5 1.2-1.8 780-1170 LGerbera 5.5-6.5 1.6-2.0 1040-1300 MGladiolus 5.5-6.5 1.6-2.4 1040-1560 MImpatien 5.5-6.5 1.8-2.0 1170-1300 MKangaroo paw 5.5-6.5 2.0-2.4 1300-1560 MLimonium 5.0-6.5 1.6-2.0 1040-1300 MMarigold 6.0-6.5 1.8-2.4 1170-1560 MMonstera 6.0-6.5 1.2-1.8 780-1170 MPalms 6.0-7.5 1.6-2.0 1040-1300 MPansies 6.0-6.5 1.8-2.4 1170-1560 MPoinsettia 6.0-6.5 1.2-1.8 780-1170 MRose 5.5-6.0 1.8-2.2 1170-1430 MSnapdragons 6.0-6.5 1.0-1.2 650-780 LSpathiphyllum 6.0-6.5 1.2-1.8 780-1170 MStock 6.0-7.0 1.6-2.0 1040-1300 MSweet pea 6.0-6.5 1.8-2.4 1170-1560 M

(EC conversion to ppm x 650)

Conductivity Factor (cF) as measured by a cF meter is an old unit ofmeasurement that uses a multification factor of 10 (i.e 1.0 mS/cm =cF 10). This term is used in the UK, NZ, and by some growers inAustralia.

Total Dissolved Solids = TDSTDS is the total mass of inorganicdissolved solids in a solution,expressed as ppm or mg/L. There arealso meters that imply that theymeasure TDS in ppm. Unfortunately,this is not strictly correct, becausethey are actually giving converted ECreadings and the conversion factor isoften in error.

pH and EC valuesThe pH and EC values specified hereare given as a broad range. It shouldbe noted that plant requirementswill vary according to plant variety,stage of growth, regional and microclimatic conditions and season. As ageneral rule, plants will have ahigher nutrient requirement incolder regions or during coolermonths, and a lower requirement inhotter regions or warmer monthswhen plants take up and transpiremore water than nutrients.

HERBS pH EC ppm ClassBasil 5.5-6.5 1.8-2.2 1170-1430 MChervil 5.5-6.5 1.8-2.2 1170-1430 MChives 6.0-6.5 1.8-2.2 1170-1430 MCorriander 6.0-6.5 1.8-2.2 1170-1430 MDill 6.0-6.5 1.8-2.2 1170-1430 MFennel 6.4-6.8 1.0-1.4 650-910 LGarlic 6.0-6.5 1.4-1.8 910-1170 MGinger 5.5-6.5 1.0-1.2 650-780 LLavender 6.4-6.8 1.0-1.4 650-910 LLemon balm 5.5-6.5 1.6-2.4 1040-1560 MMarjoram 5.5-6.5 1.6-2.0 1040-1300 MMint 6.5-7.0 1.8-2.2 1170-1430 MMibuna 6.0-6.5 0.8-1.2 520-780 LMizuna 6.0-6.5 0.8-1.2 520-780 LMustard cress 6.0-6.5 1.2-2.4 780-1560 MOregano 5.5-6.5 1.8-2.2 1170-1430 MParsley 5.5-6.0 0.8-1.8 520-1170 MRosemary 5.5-6.0 1.0-1.6 650-1040 MSage 5.5-6.5 1.0-1.8 650-1170 MShallots 6.0-6.5 1.8-2.2 1170-1430 MThyme 5.5-7.0 1.2-2.0 780-1300 MWatercress 6.5-6.8 0.4-1.8 260-1170 L

FRUIT pH EC ppm ClassBanana 5.5-6.5 1.8-2.2 1170-1430 MBlueberry 4.0-5.0 2.0-3.6 1300-2340 HCherries 6.0-7.2 2.2-3.2 1430-2080 HCurrant 6.0-6.5 1.4-1.8 910-1170 MMandarin 5.5-6.5 2.0-2.4 1300-1560 MMango 6.0-6.5 1.2-1.8 780-1170 MMelon 5.5-6.0 2.0-2.6 1300-1690 MPassionfruit 6.0-6.5 1.6-2.4 1040-1560 MPaw paw 6.0-6.5 1.6-2.4 1040-1560 MPeach 6.8-7.2 2.2-3.2 1430-2080 HPineapple 5.5-6.0 2.0-2.4 1300-1560 MRed apples 6.8-7.2 2.2-3.2 1430-2080 HRhubarb 5.5-6.0 1.6-2.0 1040-1300 MStrawberry 6.0-6.5 1.4-2.0 910-1300 MWatermelon 5.8-6.2 1.6-2.4 1040-1560 M

Low (L) Medium (M) High (H)0.6 mS/cm 1.5-2.4 mS/cm 2.4-5.0 mS/cm

Peppers grown in DFT.

Brussel sprouts grown in aggregateculture.

Nutrient strengthFor most plants the totalconcentration of nutrient elements ina solution should be between 500 and1500 ppm so that osmotic pressurewill facilitate absorption. However,some plant varieties, such as largetomatoes, may require a nutrientconcentration well over 2000 ppmduring fruiting. Lower values arepreferred by low-feeding plants suchas watercress.

Strawberries grown in NFT.

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culture, sawdust culture and aeroponics. Aggregates include a broadrange of materials: crushed granite, river pebbles, brick shardsvolcanic cinders, blue metal gravel, polystyrene mulch, in additionto the more popular types such as scoria, vermiculite, perlite andexpanded clay. The choice between these will depend on factorssuch as availability, cost and type of growing system.

The moisture retention of a medium is one of the mostimportant characteristics and is influenced by the size, shape andporosity of the particles. Water is retained on the surface of theparticles and within the pore space. The more porous the material,the greater the quantity of water that can be stored within theparticles themselves and thus the higher the water retention of themedium. Smaller particles are more water retentive than large onesbecause they have proportionately greater surface area and porespace, and they pack together more tightly.

But the moisture-retention factor is only half the equation.Drainage must also be considered, and indeed a highly retentivemedium will be of use only if it can also drain freely. This allows foradequate aeration and oxygen movement around the root zone.Because a balance of water and air is needed in the root medium,growers often find that a mixture of different mediums give the bestresult – for example, two aggregates of different sizes. Afterwatering, 10 to 20 per cent of the volume of a medium should beoccupied by air and 35 to 50 per cent by water.

Another more technical characteristic of suitable hydroponicmediums is the ‘cation exchange capacity’ (CEC). Cations areparticles which have a positive charge, and many important plantnutrients (for example, potassium, calcium, magnesium and iron)occur in the nutrient solution as cations. These nutrient particlesattach themselves to medium particles which have a negativecharge, thereby staying in the medium and not quickly leachingaway. As a result, they are available to the plant roots for longer.Mediums that attract a large number of cations are described ashaving a high CEC – a desirable characteristic. Clearly, hydroponicmediums with a high CEC require less-frequent application ofnutrients than those with a low CEC. Peat and vermiculite areexamples of mediums with a high CEC, while sand, perlite andpolystyrene mulch have low CEC ratings.

Hydroponic mediums must be free of all toxic materials, andsalt, and should not influence the pH of the nutrient solution. Theyalso need to be durable, so that they don’t disintegrate or lose theirstructure; this would lead to compaction and hence poor rootaeration. NFT System

Cation exchangeThe ability of a growing medium tohold various nutrients, includingammonium-nitrogen, potassium,calcium, magnesium, iron,manganese, zinc and copper. A rootmedium with low cation exchangecapacity does not retain nutrientswell and so must be fertilised often.

One of the first steps in establishing a hydroponic system isto choose a growing medium. There are several optionsand it is worth examining their relative merits.

Many growers find that mixes of different mediums work wellfor them though finding the right combination might be a questionof trial and error. Most importantly, you should know thecharacteristics of a growing medium before buying it and ensurethat it suits the type of hydroponic system you are using.

The medium, or ‘substrate’ used in soilless culture is morethan simply a means of support for plants. For best results it mustalso provide oxygen, hold water effectively and offer good drainage.The type of medium used determines the method of nutrientapplication: if the medium can draw liquid upwards by capillaryaction, then the nutrient solution can be applied from underneath.Media that does not have this capillary capacity but are usedbecause of other advantages require watering by surface methodssuch as trickle, drip or spray.

Essentially, hydroponic media need to be ‘inert substrates’ –neither contributing nor altering nutrients, thereby giving thegrower complete nutritional control. Hydroponic systems arebroadly grouped, according to the type of medium used, into waterculture (NFT), aggregate culture, rockwool culture, coco peat

Hydroponicmediums andtechniques

Recirculating systemsSystems in which the nutrientsolution is recycled and re-used.These are also known as ‘closed’systems. Different systems can beeither run continuously, as with NFT,or intermittently, as with the flood-and-drain technique.

Non-recirculating systemsSystems in which the growingmedium is fed with fresh nutrientsolution to replace what the plant hasused, with a slight excess displacedthat is not recycled through thesystem. Also known as ‘open’ or‘free-drainage’ systems.

A cross section of plants growing in acombined gravel and sand mixture

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dependence of NFT on reliable supplies of water and power. If abreakdown occurs, and suitable back-ups do not exist, the growercan suffer more serious losses than in media systems where thereis a degree of buffering.

grower can suffer more serious losses than in media systemswhere there is a degree of buffering.

Aggregate culture

SandSand is probably the oldest hydroponic medium known. However,not all are alike and not all are suitable for use in a hydroponicsystem. Granitic or silica-type sands should be used, not calcareoussands, which are too alkaline. Beach sand is generally unsuitablebecause of its high levels of salt, though some coastal hydroponicinstallations have used it successfully by thoroughly washing andleaching it first. If you wish to do this in a homegarden situation youwill need to chemically test the sand after washing and before use.

Sand used in hydroponic systems should not be excessivelyfine, since this can cause poor aeration and puddling, indicated bywater coming to the surface upon vibration of the sand. The ideasand aggregate is river sand washed free of fine silt and clay. Theparticle size should be between 0.6 mm and 2 mm in diameter,which allows the aggregate to drain freely and not to puddle afteran application of water. Some growers use a combination of sandsizes: 30 to 40 per cent of 5 mm, 40 to 60 per cent of 2 to 5 mm, and5 to 15 per cent of 2 mm. Coarser sands offer faster drainage in cold,damp climates but can dry out rapidly in hot areas. Before usingsand, wash it to remove any chemical impurities, dust and silt.

Sand-culture trials were being conducted as long ago as the

PuddlingPuddling or water-logging is causedby a high percentage of silt and finesand. Examples of puddling can oftenbe seen in footsteps while walkingalong wet beach sand. Whenpuddling occurs, plant roots areconstantly immersed in nutrientsolution, which can kill the plant.

A cross section of a sandbed

A hydroponic sandbed growingmustard lettuce.

Water cultureIn typical nutrient film technique (NFT) systems, plants are grownin channels or gullies so that roots are bathed to a depth of about 2 mm in a thin film of continuously flowing nutrient solution. NFTsystems are usually of the recirculating type. The nutrient solutionflows past the plant roots then drains back to the nutrient reservoirwhere it is recirculated with a pump.

The NFT system was originally designed and developed byDr Allen Cooper of Sussex, England. It is officially defined as asystem in which ‘a very shallow stream of water containing all thedissolved nutrients required for growth is recirculated past the bareroots of crop plants in a watertight gully’. Ideally, the depth of therecirculatory stream should be very shallow, little more than a filmof water – hence the name nutrient film technique. This ensures thatthe thick root mat, which develops in the bottom of the gully, has anupper surface which, although moist, is in the air. Consequently,there is an abundant supply of oxygen to the roots of the plants.

Since their development, NFT systems have changed little indesign. However, to get the best results, some understanding isrequired of the needs of different crops. For example, plants such aslettuce only require a low concentration of nutrient solution foroptimum growth, and because of their small root structure they areideally suited to NFT systems. However, tomato plants require astronger nutrient solution and a larger channel size in order toaccommodate their large root structure. Plants with a large rootstructure may restrict the flow of nutrients through the gully oncethey reach maturity.

NFT systems are used to grow lettuce, many Asian andMediterranean herbs, endive, cucumber, zucchini, capsicum,strawberry, silverbeet, and many other leafy vegetables and herbs.They are not suitable for growing root or tuber crops.

The main advantage of the NFT system is that plant roots areautomatically exposed to adequate supplies of water, oxygen andnutrients. In other types of systems, an imbalance of one of thesethree can result in an imbalance of one or both of the others.Because of its design, NFT can meet all three requirements at thesame time, producing high yields and high-quality crops fromhigh-density planting.

The disadvantage of NFT is the risk of flooding, waterloggedroots, or other problems due to poor design, construction oroperation which can cause crop losses. These problems can beavoided if growers follow the simple principles of NFT systemsoutlined here. Other disadvantages are associated with the

NFT (nutrient film technique)A water-based system wherenutrient solution flows downchannels or gullies and isrecirculated. A basic principle of thetechnique is that the nutrientsolution should be maintained as athin film to enable adequateoxygenation of the solution.

Typical NFT channel with a removablelid.The nutrient solution drains into a collector.

Australian designed channel profileknown as Ell-Gro

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surface, including bedrock or stony ground. Ground beds shouldbe lined with plastic with a length of agpipe running down thecentre to facilitate the removal of excess nutrient solution. Bedsshould be about 400 mm deep, with the agpipe buried in blue metalgravel to prevent clogging. Sand culture is an ideal technique forAustralian conditions, and is particularly well suited to rain-shadowareas. Sand beds tend to become water logged during heavy rainperiods in systems exposed to frequent rain, and can be shelteredusing clear plastic film igloos.

GravelThe characteristics of gravel are similar to those of sand, but theparticles are larger. For this reason it does not hold water as well;but, as a corollary, it has much freer drainage. A combination ofsand and gravel offers an excellent growing medium: ideally, 40 percent sand to 60 per cent medium-sized blue metal gravel, coarseriver gravel or washed scoria.

Gravel culture is among the oldest and most widely usedhydroponic techniques. It was one of the first methods used byWilliam Gericke, who pioneered the modern rival of soilless cultureusing sub-irrigation techniques. It was also the method used byAmerican GIs on coral atolls in the South Pacific during the SecondWorld War.

Gravel culture is often preferred to water culture as theaggregate helps to support plant roots. The aggregate is held in thesame type of channel tray or container as is used for water culture.The nutrient solution is held in a separate tank and pumped into theaggregate to moisten the roots as needed. After the aggregate hasbeen irrigated, enough water and nutrients cling to the aggregate tosupply the plant roots until the next irrigation cycle.

As with sand, gravels of calcareous origin, such as limestoneand coral should be avoided, since they increase the alkalinity of thenutrient solution. This makes iron unavailable to the plants and alsocauses soluble phosphates in the solution to become insoluble.

The best choice of gravel is crushed granite of irregular shapeor blue metal, free of fine particles less than 2 mm in diameter andcoarse particles more than 15 mm in diameter. At least half the totalvolume of gravel should be about 10 mm in diameter. The gravelmust be hard enough to resist breaking down over time, it must beable to retain moisture in the void spaces, and it must drain well toallow for good aeration. Other types of aggregate mediums includevermiculite, perlite, expanded clay, scoria, versarock, zeolite,pumice, smooth river-bottom pebbles and crushed marble. A hybrid NFT-Gravel system growing

snapdragons.

mid-nineteenth century, and the first published attempt to developthe commercial potential of hydroponics, which occurred in Americain 1929, used sand as the growing medium. Still widely used today,sand culture is well adapted to desert areas such as the Middle Eastand North Africa. Because of its low cost and its accessibility, it iswidely used by home gardeners.

The sand culture system has many advantages, not least thecost. It can be used as an open (free-drainage) or closed system. Theexcellent capillary action of sand results in lateral movement of thefeeding solution so that there is an even distribution of nutrientsthroughout the root zone. Additionally, the smallness of the sandparticles enables good water retention, necessitating fewer irrigationcycles during the course of a day. Unlike other systems, particularlyNFT where there is no medium, in the event of a fractured pipe,power or mechanical failure, there is more time available to repairthe system before plants consume existing water in the medium andbegin to experience stress due to dehydration. Practical advantagesof sand culture include lower construction costs, simplicity ofoperation, and easy maintenance and service.

One of the few disadvantages of sand culture is the need touse chemical or steam sterilisation between crops in order todestroy medium-borne pathogens. Although time consuming, thismethod is at least thorough. Salt build-up is another commonproblem, but this can be corrected by flushing the mediumperiodically and carefully monitoring the drainage water forevidence of salt accumulation. For some home gardeners thegreatest disadvantage of sand culture is the high consumption ofnutrients in free drainage systems. However, with carefulmanagement, the waste should account for no more than 10 per centof the total nutrient solution added.

A drip- or trickle-irrigation system must be used with sandculture. Sand beds require a slight gradient (1:400), and a single 13mm black polyethylene pipe is run down the length of the bed withmicro ‘spaghetti’ line inserted every 30 mm. In large beds, run the13 mm poly piupe along the inside of each plant row.

Irrigation emitters can be used to deliver nutrients at regularintervals, which should be two to five times daily, depending uponthe maturity of plants, weather and seasonal factors. In free drainagesystems, a sample of excess or drain water should be taken twiceweekly and tested for total dissolved salts. If the dissolved saltsreach 2000 parts per million, then you should use fresh water toleach the entire sand bed free of salts.

Sand beds can be constructed on waist-high benches, or on any

Silverbeet grown in a trickle-feedingsystem over a shallow bed of fine-gradegravel.

Coriander grown in a bench-height sandsystem using drip irrigation lines.

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Lightness is also a big advantage, making this material easy for thehome gardener to handle.

The pH of perlite is fairly neutral – in the range of pH 6.5 to7.7. Another vital feature is that it improves drainage of soils andprovides the aeration that is so important to hydroponics. It can beused on its own as a growing medium or, in situations whereadditional water retention is required, it can be used in conjunctionwith vermiculite, usually in a ratio of three to one.

Unlike vermiculite, perlite has no cation exchange or pHbuffering capacity and contains no mineral nutrients. It has a strongcapillary attraction for water, making it an efficient user of sub-surface irrigation. The rigid structure of perlite gives it excellentaeration over its lifetime which, with careful handling, can be overseveral crops.

Expanded clayThis medium is also known as LECA – light expanded clayaggregate. It is formed by blending and firing clay in rotary kilnsand looks like small irregular balls. Expanded clay is a porous,lightweight substrate with excellent capillary properties. Theinternal structure quickly absorbs the nutrient solution, carrying itto plant roots, and the pebbles are light enough to ensure good airpenetration. The structure and design of the clay pebbles alsoprevent decomposition and build-up of acids in the medium, andthe pebbles have a very stable pH.

Because of its natural earthy appeal, expanded clay is widelyused as a growing medium for indoor potted plants and for manysimple hydroponic systems. Where algae is a problem, however, thesmall pore size of expanded clay can cause clogging.

Although expanded clay is imported into Australia, its cost isnot as prohibitive as it once was. As a result, it is proving a popularmedium for more sophisticated systems, particularly for flood-and-drain systems where it has proved an excellent medium.

ScoriaScoria is a hard volcanic rock full of air pockets once occupied bygases. It is commonly but not always basaltic or andesitic incomposition. The word comes from the Greek skoria for ‘rust’, areference to its typical red colour, although it can also be dark brownor black. An old name for scoria is cinder. Available throughout theworld where there is volcanic activity, a unique form of scoria isquarried at Mount Quincan in Far North Queensland.

Scoria is commonly used in landscape design where its unique

Expanded clay is popular among homegardeners because of its excellent capillary

properties and its natural, earthy look.

Gravel culture systems can be adapted to either NFT, using channelfilled with gravel; or drip-irrigation systems. (See Choosing a system).

VermiculiteThe structure of vermiculite is similar to that of mica. This flaky mineral ismined in Africa, China, Brazil, the USA and Australia. Flakes of rawvermiculite contain silicates of aluminium and iron. These flakes are heatedin a furnace to very high temperatures in a process known as exfoliation.The moisture inside turns to steam, splitting the layers apart and creatinglight, spongy particles which are excellent for hydroponic mixes. Theprocess expands the ore particles some twenty-fold, and the very light, soft,glittering particles so formed will retain water up to 50 per cent by volume.

Vermiculite has a pH of 7.0, but it can at times turn slightlymore alkaline. Like perlite, it is sterile and free from harmfulorganisms. Its excellent water retention properties make it an idealadditive to hydroponic mediums in situations where drying out islikely to be a problem. In passive hydroponic systems it has a natural‘wicking’ property that can draw water and nutrients. If too muchwater and not enough air surrounds the plants roots, it's possible togradually lower the medium's water-retention capability by mixingin increasing quantities of perlite. The best results are achieved usinga combination of perlite and vermiculite at a 3:1 ratio.

Vermiculite contains some magnesium and potassium, whichit releases to plants growing in it. It also has a relatively high cationexchange capacity and good buffering properties (that is, it can resistchanges in pH).

The disadvantage of vermiculite is that, unlike otherhydroponic media, it tends to break down over time, which mightlead to clogging of tubing and filters in a recycling system, anddrainage reduction leading to stagnation in simpler systems.

PerlitePerlite is a volcanic mineral that resembles small, black crystals ofsand when it is minded. On being heated to a temperature of 10000Cthese crystals explode like popcorn and form soft white or greygranules which have a foam-like texture. The expanded mineral isvery light, each particle being honeycombed with tiny air bubbles.These bubbles or air pockets can hold water or nutrients and thenrelease them to the roots of plants. However, they are less spongybut better drained than vermiculite and the two mediums make acomplementary mixture.

Among the more important features of perlite is sterility: whenmanufactured the material is free from disease and organic matter.Perlite is lightweight and often used with

vermiculite as a growing medium.

Vermiculite is lightweight and easy towork with. Many gardeners will befamiliar with the mica found in seedlingmixes.

Roses grown in Perlite.

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PumicePumice, like perlite, is a salicaceous rock of volcanic origin. Itslightweight is derived from the inclusion of gases in the magmafrom which it is formed. It does not undergo any heating process. Itis simply crushed and screened before use. Pumice is heavier thanperlite and does not absorb water as easily. It is pH neutral with alow cation exchange capacity. However, it does hold more waterthan gravel particles of similar size. It is sometimes used in a mixwith peat and sand, but it is a very good hydroponic medium on itsown. Widely available in New Zealand, high transport costs limitits availability in Australia which doesn’t have local deposits.

Plastic foamAvailable in pellet form, these materials are chemically inert andextremely lightweight. While several different types of plasticmaterials are used, generally they do not retain moisture or nutrientvery well and, on their own, do not always provide sufficientsupport for plants. They can be mixed with other mediums, thoughsome have a tendency to float to the top over time. Plastic foamcontain no nutrients, and have negligible cation exchange capacityand poor buffering capacity. Sometimes called plastic mulch, pelletsare usually made from polyurethane, polystyrene or urea-formaldehyde.

Rockwool cultureRockwool was developed by the Danish in 1969 and is among themost popular commercial growing mediums used worldwide.Rockwool culture first appeared in Australia in 1982 with thedevelopment of Growool, a horticultural grade rockwool.

Rockwool is an inert fibrous material made from a mixture ofvolcanic rock, limestone and coke which is melted at a temperatureof 15000C to 20000C. The molten substance is extruded as finethreads and pressed into sheets and then cubes. Surface tension isreduced by adding a phenol resin during cooling. A different formof rockwool is used in the building industry as an insulationmaterial; this is not suitable for horticulture.

Horticultural-grade rockwool is noted for its good air- andwater-holding capacity, containing about 3 per cent solid and 97 percent pore space. Root growth tends to follow the direction of thefibres, and the fibre can be aligned either vertically or horizontallyto suit the growth required. For propagation, the fibres areorientated in a vertical direction to allow downward rootdevelopment. The cubes can then be placed on a slab to allow

Rockwool culture is popular among homegardeners. Seeds can be started in smallcubes, then transferred to larger cubes

before final placement on a rockwool slab.

Pumice is a light-coloured rock, which iscreated when super-heated, highly

pressurised rock is violently ejected from avolcano. .

colour gives it an earthy, natural look. Like other crushed rocks itmay be slightly alkaline, from pH 7 to 10, and contain salts, thereforeit needs washing before use as a hydroponic medium. The nutrientsolution may need frequent adjustment for a while. Scoria can becrushed to any size but sand-size particles from 0.5 to 2 mm behavelike perlite although scoria has a higher bulk density.

VersarockVersarock is a rarely used medium in Australia. It is derived froma volcanic ash of rhyolitic (granitic) composition. Mineralogically, itconsists of kaolinite and opal C-T, with some other minorconstituents. Essentially, versarock is a naturally occurring premixedceramic.

Versarock is inert, is highly absorbent and can be milled to anyparticle size. It has an extremely porous structure but does notdisaggregate in water. Air penetration through the medium is gooddue to the odd shape of the stones, which can have four, five or sixfaces, meaning that they do not ‘marry’ well in a mixture. It islightweight and has some cation exchange capacity.

One of the useful characteristics of versarock is that it changescolour when dry, enabling the gardener to assess the moisturestatus of the system just by looking at it. The material has goodinsulating properties and is very slow to heat up and cool downdue to air entrapment within the pores. Versarock is inert and iseasily pH stablised. It is sterilised before sale and is user-friendly –it can be recycled again and again, and does not float or blow awayin the wind.

ZeoliteZeolite is another rarely used hydroponic medium in Australia. It isa naturally occurring mineral which, because of its high cationexchange capacity, is used as a soil additive. The material has anunusual cage-like molecular structure with the ability to exchangeplant nutrients freely.

The major minerals in zeolite are naturally occurring silicates.Found around the world, different zeolites vary in hardness (hencedurability) and in the proportions of different cations they contain.Zeolites mined in Australia are mainly loaded with calcium withmoderate levels of available potassium. It is gravel-like inappearance and reasonably heavy. Some research has beenconducted in the US into using a mixture of zeolite and anothermineral, apatite, as a hydroponic medium.

Ginger grown in zeolite

Aggregate cultureAggregate mediums anchor plantsand also retain solution betweenirrigations in different ways. Sand,perlite and vermiculite retain moresolution than gravel, so irrigationfrequency can be less with thesesubstrates than with gravel. Itshould be noted that good aerationmay be unsatisfactory if more thanabout 30 per cent of the particles aresmaller than 0.5 mm. Sand must be mainly quartz or

other relatively inert materials.Calcareous sand that contains limeand/or dolomite is unsuitable as ahydroponic medium unless it isthoroughly leached before use, andeven then the pH of the solution mayneed frequent adjustment.

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prohibitive. However, the fact that it can be used several times overcompensates for this by reducing overall costs.

To prevent minor skin irritation the user should wear glovesand a long sleeve shirt and should wet the rockwool beforehandling it.

As in the case of NFT, plants can be propagated at a highdensity in small rockwool cubes in a specially regulatedenvironment. They can then be spaced out into a moderately highdensity area of the garden by placing these cubes on top of rockwoolslabs positioned on benches or trays. Slabs can also be placed on theground by using thick plastic between the soil and slab.

Rockwool culture does not demand an even surface like NFTdoes, as slabs are wrapped in polyethylene plastic, which preventsdrainage to the lowest area along the bed. In tropical climates theplastic is usually omitted to allow for evaporative cooling of theroot zone. However, plastic is still used between slabs, to preventwicking of the nutrient solution, a lack of solution in high spotsand excess solution in low spots, and spread of any disease thatmight occur.

Narrow slabs (150 mm wide) are placed end to end in a doublerow to form a bed for cucumbers, tomatoes and roses. For other freshflowers, wider slabs (300 mm wide) are used to line a bench. In bothcases, cubes are used for individual plants, which are then placedon top of the slabs.

Plastic-lined slabs should be cut near the bottom of the sides,halfway between plants, as well as the ends of the slab. This willforce nutrient solution to move horizontally throughout the slab.

Irrigation of the slabs can be via drippers, or by NFT, usuallyabout three times a day. Ultimately, the frequency of irrigation willdepend upon plant mass and weather conditions. For drip irrigation,the nutrient solution is delivered through micro-tubes from a PVCplastic pipe (15-20 mm) running along the bed.

A 150 mm thick slab of rockwool can hold about half of its porespace in water. However, the distribution of solution is unequal,with the lower part holding nearly all of the water and the top lessthan ten per cent. For 75 mm thick slabs, the water-holding capacityis 77 per cent of its pore space, leaving 20 per cent of the pores openfor aeration.

Rockwool is an excellent medium for free drainage systems.This irrigation practice lessens the chances of disease since thenutrients are not recirculated. Additionally, much of the expensivesolution-handling equipment and the electrical energy required byNFT are eliminated.

horizontal root development. Rockwool is not biodegradable and contains no soluble

materials. Therefore, as required it does not contribute nutrient orforeign substances to the culture system during use. The cationexchange capacity is negligible, so applied nutrients are notabsorbed, and nutrient availability is dictated by the nutrientsolution required.

Rockwool has no pH buffer capacity; that it, it has no effect onthe pH of the nutrient solution, other than when it is wet for the firsttime. On its initial wetting the rockwool will raise the pH of thesolution by about 1 pH unit, which can be compensated if required.For feeding thereafter, a free drainage or rockwool-specific nutrientformulation can be used as a feed pH of typically 5.2 to 6.2.

Many users of rockwool condition the substrate to moisten theslabs uniformly and, according to some rockwool practitioners, toadjust the pH before transplanting and thus allow standard nutrientformulations to be used. Conditioning is achieved by soaking theslabs in a nutrient solution for 24 to 48 hours. To do this, lay the slabsin their final resting position with three drip lines positioned at thetop of each slab at equal spacing. Do not slit the sides or ends ofplastic-lined slabs until the rockwool has been completely soaked inthe nutrient solution.

Horticultural rockwool is available in many shapes and forms,ranging from small propagation blocks or cubes to slabs up to 1500by 300 by 100 mm. Larger cubes are usually wrapped in plastic toprevent evaporation and the spread of roots into adjacent slabs.Large cubes can be obtained with a depression in the top into whichsmaller propagation cubes can be inserted for transplantingpurposes. Granulated rockwool, sometimes called ‘floc’, is availablefor pot culture, or for adding aeration to potting mediums, used atthe rate of 33 per cent of the medium volume.

Rockwool is an excellent inert substrate for both free drainageand recirculating systemsd. In free drainage systems the chance ofdisease spread is greatly lessened by the medium. Rockwool is alsolightweight and self-contained, which allows plants to be grown atdifferent densities in different stages: young plants can be grown toan advanced stage in a small area before being planted out into themain growing area, thus improving crop turnaround. Its lightweight also makes it quick and inexpensive to set up. Its lightnessand rigidity eliminate the need for back-breaking work inpreparation and planting.

The disadvantages of rockwool are few. Although relativelyinexpensive, its bulk can make transport costs to remote regions

Rockwool cubes are placed on top of slabsin this recirculating rockwool system.

Rockwool cultureIn wrapped rockwool installationsthe drainage holes must be cutbetween the drippers and at bothside of the rockwool slab. Ensurethat the outlets under the slabs areremote from drippers so that thewhole slab can be used and excesssalts leached away.

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the exception of jarrah, must be detoxified by composting before use. Owing to microbial activity and chemical breakdown, sawdust

needs to be replaced after each crop. Hardwood and softwoodsawdust are used as growing mediums, however raid decompositioncan cause 50 per cent volume loss over the space of a year, with acorresponding slump in air-filled porosity. The microbes that causethis decomposition have a high demand for soluble nitrogen, thushigher concentrations of nitrogen is needed in the feed solution. Notall sawdust can be used for hydroponic purposes.

The two methods used for sawdust culture are the pot and bagsystems. The former uses moderately deep (200-250 mm) plastic potswith suitable drainage holes for free drainage feeding. Bag systemsuse polyethylene bags with holes punched in the bottom to allowgood drainage. Bags can be either suspended from rafters, or set onthe ground: a plastic sheet should separate the bag from the groundso that roots do not grow out the drainage holes and into the soil.Polyethylene garbage bags can be used by the home gardeners, butthese must be set on the ground because of the weight of the sawdust.Twenty-litre plastic pots with drainage holes can also be used.

The ideal feeding system is drip irrigation or a trickle-feedingsystem. Seedlings can be started in rockwool cubes, then transplantedto the sawdust.

AeroponicsAeroponics is defined as a system in which the plants’ roots arecontinuously or discontinuously in an environment saturated withfine drops (a mist or aerosol) of nutrient solution. The methodrequires no substrate and entails growing plants with their rootssuspended in a deep air or growth chamber, with the rootsperiodically wetted with a fine mist enriched with nutrients.

Since its development the aeroponic technique has provedvery successful for propagation, but has yet to prove itself on a largerscale. It is widely used in laboratory studies of plant physiology, andis also used in the USA to research controlled environment lifesupport systems to be used in space stations of the future, and tosupport visitors to Mars.

The main advantage of aeroponics is the excellent aeration itgives plant roots. Trials of this system have detected a significantrelationship between low water level and increased air space; theimportance of oxygen in supporting the intensive metabolicprocesses associated with root formation and subsequent growth iswell recognised.

Aeroponic techniques are noted for thedevelopment of large root structures.

Coco peat cultureCoco peat, also known as coir pith, coir fibre, coir dust or simply coir,is made from coconut husks, which are by-products of other industriesthat use coconuts. It is an organic medium where the coconut husksare washed, heat-treated and graded before being processed into cocopeat products of various granularity and densities, which are thenused for horticulture and hydroponic applications.

For hydroponic applications, coco peat culture uses systemssimilar to rockwool culture, where the medium is contained inplastic bags or is available as a loose medium for pot culture. Itusually comes in the form of compressed bales, briquettes, slabs ordiscs that expand and aerates with the addition of water. A kilogramof coco peat will expand to 15 litres of moist coco peat.

Coco peat has a similar cation exchange capacity to sphagnumpeat. It holds water well, rewets well when dry and holds around1000 times more air than soil. Coco peat contains several macro- andmicro-plant nutrients including calcium, magnesium and potassium.Additionally, it is not fully decomposed and like sawdust it will useup and compete for nitrogen (known as nitrogen drawdown) in thenutrient solution if there is not enough. Poorly sourced coco peat canalso have excess sodium in it and needs washing before use as agrowing medium. Growers should check the EC of the run-off waterand flush the medium if it is high. Good quality coco peat will benear neutral pH. Coco peat can be used up to three times with littleloss of yield.

Coco peat can be safely used for recirculating and flood anddrain systems. For faster drainage it can be mixed with perlite,pumice or expanded clay. Because it is an organic media, disposal iseasy and environmentally sound.

Sawdust cultureSawdust culture is mainly used in Canada and South Africa, and hasbeen tried with mixed success here in Australia. Because of its lowcost and light weight it has proved popular with some homegardeners. A significant advantage of sawdust culture is less chanceof disease, because it is an open or free drainage system. Otheradvantages include good lateral movement of the nutrient solutionthroughout the root zone, good aeration and high water retention.

Over the cropping season, salt may accumulate in the mediumto toxic levels, starting from the bottom of the growing column andworking its way upwards. This can be reduced by regular leachingwith fresh water. Since sawdust is organic in nature, it alsodecomposes with time. All softwood and hardwood sawdust, with

Homrgrown tomotoes grown in a coco peat slab.

AeroponicsA system where the roots of a plantare continuously or intermittently inan environment saturated with finedrops (a mist or aerosol) of nutrientsolution.

Larger bags of coco peat are available fromnurseries and specialist hydroponic retailcentres.

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The most popular form of NFT system for the home gardenerand commercial grower consists of rectangular, pre-fabricated rigidchannels with removable lids. These channels, also known asgullies, can be set on simple, waist-high tables to allow easy accessfor the gardener. Rainwater downpipes also make practicalchannels, but they are difficult to clean between crops. Round PVCpipe and trays with curved bottoms have also been used; but,because of their shape, a nutrient film cannot be established androots quickly block the flow of nutrient, leading to early floodingand water-logging. Such channel profiles are not recommended,even though their low cost is tempting.

A variation of rigid channels is inexpensive black-and-whiteflexible plastic or water-proof tarpaulin. The floor or surface needsto have a slight angle to permit the film of water and nutrients togravitate downwards to a collection receptacle from where it isrecycled. Such channels need to be about 200 mm wide, with thetwo equal sides folded and supported across the top to form aninverted ‘T’. The nutrient film flows along the floor of the channel.The black inside excludes light and the white exterior reflects lightand heat. To assist crop establishment, a small piece of rockwool orcapillary matting can be placed under young seedlings while rootsdevelop.

A support wire, about 200 mm above the channel base servesto keep the channel in shape and bolster young plants. Duringoperation, the ‘tent’ shape must be maintained to allow adequateaeration. The plastic should not be allowed to collapse and makecontact with the tops of the plant roots, otherwise air will beexcluded from the channel.

Flood-and-drain systemThe flood-and-drain (also known as ‘ebb-and-flow’ and sub-irrigation) system is a closed system widely used by homegardeners, being especially suited to growing herbs and seedlings.The technique uses any of a variety of different media, includingexpanded clay, scoria, river pebbles, rockwool, coco peat or pumice.It consists of a shallow table with an inlet and an outlet valvesituated at the bottom of the tray. Once hourly, or less oftenaccording to the climatic and environmental conditions, the tableis flooded for about fifteen minutes then drained to allow plantroots to aerate. Once the water level has reached a set depth duringthe flood cycle, an overflow valve allows the nutrient solution todrain back into a reservoir where it is recirculated by a pump,thereby providing a continuous flow of fresh nutrient solution to

With the exception of the NFT system all hydroponicsystems are suited to all plants. The choice depends onmany factors – the size of your garden, the type of

construction you prefer, how much automation you decide to useand, of course, your budget. For example, for a small courtyard orbalcony, where space is extremely limited, a system that is tiered willmaximise the available space, allowing you to grow an array ofplants to produce crops and/or enhance the aesthetics; and the levelof automation you choose is governed by your budget, and/or yourcommitment to maintaining such a garden on a regular basis.

Systems are categorised as either ‘open’ or ‘closed’. An open(non-recirculation) system is a ‘free drainage’ system, which meansthat the nutrient solution passes the root zone only once before it isdiscarded. The most popular free drainage systems use gravel,scoria, sand, rockwool, coco peat or sawdust as the medium. Inclosed systems the nutrient solution is continuously recirculated andcan be adapted to NFT or rockwool/coco peat systems, flood-and-drain tables, drip-irrigation systems or aeroponic chambers.

NFT systemThe NFT system is a closed system and is simple to set up on a smallscale. A large amount of water is required per plant and the solutionmust be aerated continuously. Various techniques can be used toaerate the nutrient solution, but it is usual to replace the solution atregular intervals or to agitate the solution with a small aquariumpump and air stone.

While the size, design and construction can vary between largecommercial units, research laboratory units and units designed forthe small home gardener, the basic principles of NFT remain thesame. The essential components consist of a cultural vessel to holdthe plant’s roots, a nutrient reservoir, a submersible pump andirrigation fittings.

Choosing a system

Some of the different rigid channel profilesavailable to the home gardener.

A typical flood-and-drain or sub-irrigationsystem used for seedlings. Polystyrene is

used here to float seedlings on the nutrientsolution between watering cycles.

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nutrient must be entirely soluble in water, otherwise the micro-irrigation tubes and emitters may clog. Such systems can be usedwith a variety of substrates, including rockwool, coco peat,expanded clay, gravel, sand, perlite/vermiculite, scoria, pumice,versarock, sawdust and zeolite. The watering regime is dependentupon the characteristics of the substrate as well as environmentalfactors.

The advantages of drip irrigation systems include increasednutrient efficiency, low construction costs, reduced labour andenergy costs and greater flexibility in tailoring the timing of nutrientapplications to crop demands regardless of plant growth stages.Other advantages include good aeration in the root zone, since watertrickling down carries fresh air with it and at no time are the rootssubmerged in water.

The main disadvantage of drip irrigation methods is that somenutrients can cause clogging. A liquid concentrate is more suitablethan powdered nutrients, but you should ensure that no sedimentis resting at the bottom of the concentrate and that micro-nutrientsare in chelated form to reduce the possibility of clogging. The use ofan in-line filter in the main feed line will help reduce clogging.If gravel is the main substrate, then ‘coning’ of water movement maysometimes occur due to the relative coarseness of the medium. Thismeans that water flows straight down rather than moving laterallyin the root zone. The result is a water shortage to plants and rootsgrowing along the bottom of the bed where most water is present,eventually plugging drainage holes and pipes.

The bed design and construction of a drip-irrigation systemare similar to those of sub-irrigation systems but simpler. Thesimplest system entails a 13-mm or 10-mm black poly tube runningfrom the nutrient reservoir along the bed, which is then ‘blanked’ atthe end of the garden bed. From this central irrigation line, 4-mmmicro tubing (spaghetti tubing) is inserted at regular intervals. Thesemicro-irrigation lines must be long enough to reach the base of theplants that they are to feed.

To control the flow of the nutrient feed cycle, adjustableemitters can be used in the spaghetti lines or, alternatively, a tee anda tap can be inserted in the main irrigation line before it leaves thenutrient reservoir. The pressure flow of the system can then becontrolled by opening or closing the tap. The advantage of the lattermethod is that excess water is returned to the reservoir, which inturns aerates the nutrient solution. Beds should be well drained,with excess nutrient solution either run-to-waste or returned to thenutrient reservoir for recycling.

This drip-irrigation system has anoverhead main feed line, and 4-mmadaptor to provide irrigation to the

medium and plants.

Drip- or trickle-irrigation In drip- or trickle-irrigation systems,water is applied slowly andfrequently to a limited part of theplant’s root zone through devicessuch as drippers or emitters. The aimis to ensure that plants are never shortof water and nutrients, so that theyare able to grow as rapidly as otherfactors allow.

Advantages• It is cheaper than other types ofirrigation systems.

• Plant growth rates are high becauseplants need never be short of waterand nutrients.

• If properly operated, less water andnutrients are used.

• Wind does not alter thedistribution of water and nutrients.

• Work can continue in the areaduring irrigation cycles.

Disadvantages• Drippers can clog.• A filter must be used to removeparticles in the nutrient solution.

the plant roots.The ebb-and-flow cycle of the nutrient solution pushes stale

air upwards during the flood cycle, and pulls fresh air downwardsto the root zone during the drain cycle. This movement of air andnutrient solution provides essential water, oxygen and nutrients toplant roots.

Unlike NFT, flood-and-drain systems have a greater bufferingcapacity in the event of breakdowns; that is, the medium holds adegree of moisture from which plants continue to derive nutrientsuntil any malfunction is corrected.

The ideal frequency and duration of the floo-and-drain cycleis important to the success of the system and depends upon:

•The type of substrate•The size of particles if using gravel or scoria•The nature of the crop•The size of the crop•Environmental factors•The time of day.Large, coarse or smooth aggregate must be irrigated more

frequently than porous, finely shaped aggregate. Tall crops bearingfruit require more frequent flooding than short, leafy crops such aslettuce. Hot, dry weather and strong light promote rapidevaporation, calling for frequent irrigation. As a general rule, threeto four daily irrigation cycles are recommended during winter, andas much as one irrigation cycle hourly is needed during the hotsummer months. A couple of irrigation cycles are recommendedduring the night. Each cycle should last 10 to 15 minutes. Irrigationcycles should fill and drain the table rapidly, and drainage must becomplete, with no residue solution left on the bottom of the bed ortable.

The speed of flooding and draining of the nutrient solutiondetermines the aeration of the plant root system. To respire the rootsrequire oxygen, which in turn provides the energy plants need totake in water and nutrients. Insufficient oxygen around the roots canretard plant growth or cause plant injury, reduce yields, and causeplant death. Essentially, the greater the movement of the nutrientsolution the greater the movement of air displacement.

Drip-irrigation systemDrip-irrigation (also called trickle-irrigation) systems can be open orclosed, but most home gardeners prefer the open option. Thesystems can be easily designed and constructed with componentsreadily available from the local hardware store. However, the

Drip-irrigation, also called trickle-irrigation, can be open or closed systems.

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The spray is created by injecting nutrient solution at relativelylow water pressure through strategically placed nozzles. Aerationand delivery of spray vary according to the design of individualsystems.

Commercial EGS installations are in operation in manycountries, with tomatoes and cucumbers the major crops grown. TheEGS system is also available as a propagation, hobby or laboratoryunit and consists of an 18 L cylindrical chamber (half-filled withcontinuously agitated water), motor and housing, and a removablecover with collared holes to support plants. It functions by drawingwater upwards from the bottom of the container through a hollow,rotating impeller, driven by an electric motor. The rate of wateruptake (2 litres per minute) is proportional to the rotating speed ofthe motor (300 rpm). The drawn water is then thrown horizontallyby centrifugal force into the air space above the water reservoir,creating a fine spray and so increasing the water surface area. Then,as the water droplets fall back into the agitated water, gas exchangetakes place.

Other types of aeroponic systems include the Rainforestsystem, developed by Californian-based General Hydroponics forthe home garden market, which is similar to the EGS system in itstechnology. It differs only in the mist or spray delivery. In thissystem a submersible pump draws water upwards through a centraltube to the top of the growing chamber where the jet of water strikesa curved plate, causing the solution to be sprayed horizontally ontothe roots in the spray zone. The circle of water (not a true spray)created then falls back into the reservoir to provide gas exchange.Work in Australia by an industrial design student in the early 1990’sled to the development of an aeroponic system that uses ultrasonictechnology to vaporise the nutrient solution, providing a fog-likemist to plant roots. The mist is much finer than any that can beachieved in conventional spray and pump systems. The mainadvantage of this system is that micro-irrigation equipment, whichis prone to blockages, is eliminated. However, the technology wasnever fully developed. A major obstacle was overheating, causingthe transducer to fail after a short time.

Theoretically, aeroponics is a good system. However, the useof hydroponics overall is dictated by economic considerations andit is here that conventional aeroponics is costly for most growingapplications. The need for expensive timing, irrigation and pumpingequipment puts it out of the reach of most home gardeners. Forpropagation and laboratory experiments, however, it is well provenand widely used.

The Rainforest modular aero-hydroponicsystem uses a circle of water to deliver

nutrients to the root zone.

Aeroponic systemIn aeroponics, plant roots grow in a closed chamber. A mistingsystem bathes the roots in a film of nutrient solution and keeps themclose to 100 per cent relative humidity to prevent drying. Thechamber can be of any size and design, as long as it is moisture proofand dark. Tomatoes can be grown in tall, narrow containers linedwith plastic. Lettuce and strawberries can be cultivated in A-framecontainers to make the best use of space and light.

Apart from the relatively high set-up costs, the aeroponictechnique is mechanically quite elaborate, susceptible tomalfunction, requires regulation and control of water andnutrients, and has no buffer capacity to sustain even slightdeviations or occasional breakdowns. If blocked nozzles ormalfunctions go unnoticed, plants can be irreparably damaged ina relatively short time.

Yet, for propagation purposes, aeroponics is well proven.Experiments in Israel to assess aeroponics as a plant propagationmethod, and to determine the effect of dissolved oxygen on therooting of cuttings, produced some interesting results. BothChrysanthemum and Ficus, noted as difficult-to-root species,responded to increased dissolved oxygen concentrations. Thenumber of roots and total root length increased as dissolved oxygenincreased. A notable commercial propagation success story usingaeroponics is the production of millions of saplings to reforestIndonesia, significantly reducing the time taken to produce youngtrees. Aeroponics technology is also used for commercial vegetableproduction including kangkung, also known as swamp cabbage andwater spinach.

The Ein Gedi System (EGS), developed by workers of theAgricultural Research Organisation in Israel, is a trough systemwhich utilises the advantages of true water culture systems toovercome the limitations of aeroponics and NFT, in effect combiningthe good points of all these systems.

The EGS is an aero-hydroponic, rather than a truly aeroponicsystem in which plant roots are immersed in a deep, circulating,continuously aerated nutrient solution. The solution is delivered intwo layers: as a spray circulated on top of a liquid. The solution isinjected into the trough by successive laser-cut apertures in adirection opposing that of the solution flow. Oxygen is carried fromthe spray zone into the nutrient solution, aerating it and providinghigh oxygen concentrations at the root surface. This permits roots tobe immersed in a deep, large volume of nutrient solution, in troughsor channels of any length, and to grow in the spray zone.

A schematic view of the Ein Gediaeroponic system.

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Other systems

Wick systemThe wick system falls into the category of a closed system and it isone of the most popular hydroponic options used by homegardeners. It consists of a double pot or container, with one sectionfor the medium and the plant and the other for the nutrient solution.A fibrous wick, such as hemp rope or linen is set into the growingcontainer about one-third of the way, with the other end suspendedin the nutrient solution below. As water evaporates from the foliageand moisture moves from the medium to the plant, capillary actiondraws more solution from the reservoir through the wick to the plantroot zone.

Such a system can be easily designed for a balcony, a windowledge, or an under-used area of the garden, and supplied from acentral nutrient reservoir. Though not essential, it is useful to havea floating marker to indicate the level of liquid in the reservoir.

Gravity/vacuum systemThe gravity/vacuum system made an appearance in the early 1990’s,utilising an age-old principle of irrigation. It, too, is a closed systemand consists of a growing tray and air-tight plastic nutrient reservoir.The water inlet to the growing tray is level with an air hose whichleads back to the nutrient reservoir. Gravity forces water into thegrowing tray to form a shallow pool of nutrient solution at thebottom of the bed. Once the nutrient pool reaches the level of the airhose, a vacuum is created in the air-tight nutrient reservoir, whichin turn prevents any more solution from entering the growing bed.

Then, as plants draw in nutrients and water, and some is lost toevaporation, the nutrient pool drops and exposes the air hose, whichin turn releases the vacuum to allow more nutrients and water toflow into the growing tray.

For the gravity/vacuum system to function correctly, both thegrowing tray and nutrient reservoir must be at the same level. Suchsystems are economical to construct and make an ideal entry pointfor beginners to learn the basic principles of hydroponic cultivationbefore moving on to more complex systems.

Gravity-feed systemThe gravity-feed system, which can be open or (more popularly)closed, has proven popular with home gardeners owing to its lowcost and simplicity of construction and operation. The key to itssuccess is the nutrient reservoir, which is positioned higher than thegrowing bed, and a collection reservoir positioned lower than thegrowing bed. The nutrient solution flows from the reservoir into theaggregate material in the growing bed, from where it drains into thecollection receptacle. The nutrient solution is then returned to thenutrient reservoir using either a foot pump or an electricalsubmersible pump. The keen gardener can interchange the nutrientcontainer and the collection container at regular intervals,eliminating the need for any electrical devices.

Self-watering potsSeveral examples of this closed system are available on the market,and are a good way of entering the world of hydroponics. The threemost popular types of self-watering pots are the Decor range, inwhich a see-through, deep saucer is attached to the main pot, andthe Luwasa and Leni Hydroculture pots, which use a plastic watergauge to indicate the level of the nutrient solution within the pot.These pots generally use expanded clay as the growing mediumbecause of its attractive, earthy appeal and good capillary mode ofaction.

The self-watering pot is the perfect system for indoor plants.The Leni and Luwasa pots consist of an inner and outer pot, withthe former perforated down the sides to allow the plant’s roots toaerate and to feed from the nutrient solution. Once the plant hasoutgrown its pot, the inner pot can be easily removed and placed ina larger pouter pot, which is then filled with more substrate such asexpanded clay. Some plant hire businesses specialise in these typeof growing systems for corporate offices, hospitals and foyerentrances, where plants can be easily maintained.

The gravity and vacuum Plant-a-Box system uses no electrical or mechanicaldevices. This system can be expanded using the same nutrient reservoir.

The gravity and vacuum Plant-a-Boxsystem uses no electrical or mechanicaldevices. This system can be expanded

using the same nutrient reservoir.

Simple gravity-feed system. The solutionflows from A into the aggregate substratein the growing table. When the growingtable is flooded, the solution is drained

into B, then returned to A, eithermanually or electrically.

Self-watering pot with water indiator.

NFT systemA number of small NFT systems are available on the market andthere are some compelling arguments in favour of purchasing these– most obviously the convenience of a complete kit that is ready toplug in. For the aged and infirm, or for anyone who leads a busylife, a ready-to-go NFT kit is a practical solution. However, you canalso custom build your own NFT system according to your specificrequirements.

The actual design of your NFT system is limited only by yourimagination. But bear in mind that the system must provide ameans to:• Support the plant above the nutrient solution• Deliver the nutrient solution• Aerate the nutrient solution• Prevent light reaching the solution so that algae doesn’t grow.

To construct your own NFT system you will need a certain level ofskill, but for many people the task is easy and enjoyable. The sizeof the installation is important, with most home gardeners settlingon a system somewhere between two and five metres long andthree to five channels wide. Long runs of channel are notrecommended, since they generate heat gradients in the channel,can slow down the speed of circulation, and do not adequatelyaerate plants at the end of the channel. The site of the system shouldbe protected from wind. If such a location is not possible, then awind screen will prove beneficial.

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The simplest and most inexpensive way to grow vegetables,herbs and flowers hydroponically is to use plastic orpolystyrene trays. The latter can be easily obtained from

your local fruiter and adapted to become a series of hydroponicgarden beds. The best types are broccoli boxes because they haveno drainage slits on the bottom. However, you will need to preparesuch trays and boxes with drainage holes about 2 cm from thebottom to provide a shallow nutrient pool from which the plantscan draw their nourishment. The concept is the same as for self-watering pots, or a standard terracotta pot and saucer.

You can hand-water the trays as required, or install a simpleirrigation system to handle automatic irrigation. Simple micro-irrigation fittings are readily sold over the counter at nurseries,garden centres and specialist hydroponic outlets. The nutrientreservoir usually consists of a small plastic pail or drum, and a fish-aquarium submersible pump will distribute the solution to thegarden beds.

To build a simple free-drainage system, you can usepolystyrene boxes with existing drainage slits. Simply fill the boxeswith snad and install a trickle ittigation feeding system in themanner just described. Irrigation cycles should be timed so thatexcess nutrient accounts for no more than ten per cent of the totalnutrient solution. You can measure this by placing a small cup orcontainer, such as a margarine tub, beneath one box to captureexcess nutrients. At the end of each watering cycle the cup or tubshould not overfill with excess nutrients. This technique may takea few days of trial and error to master.

Once you are satisfied that hydroponics is for you, you candesign more elaborate systems or upgrade and expand your currententerprise.

Building a system

This typical small NFT system is easy to construct and operate.Alternate A-frameNFT systemconfigurations.

Garden reflectorsMost vegetables need at least 6-8hours of direct sunlight a day to growproperly. Unfortunately, small citygardens may be jammed between afence and a wall, sandwichedbetween two buildings, or crammedinto an oddly shaped corner so plantsare shaded most of the day. If youhave this problem, don’t give up! Youcan add to the natural light with areflector panel or wall.

Make reflector panels bystapling or gluing aluminium foil, orsimilar materials, to large sheets ofcardboard or plywood. Make thereflector panel the same length as thegarden. If there is a wall, paint itwhite. Not only will it reflect light, itwill also provide a degree of heatwhich can be beneficial to thegrowing season.

major changes in nutrient concentration are linked to substantialpH changes, which can shock plants and cause all sorts of plantmaladies.

Reservoir siteThe nutrient reservoir determines the direction of flow in the channels.It must be the lowest component of any NFT system and must becovered so that rainwater does not dilute the nutrient solution.

Solution temperatureThe ideal solution temperature varies from one plant to another.However, for most plants it should stay between 180C and 250C.There is a danger that the solution will overheat if the channel isexposed to too much direct sun during the hot summer months.Mature plants will shade the channel to some degree, makingoverheating less likely.

Channel layoutThe standard form of NFT system uses rigid channels, but simplersystems can be constructed using standard trays. For multiple-rowchannels, the separation should be between 10 and 30 cm,depending upon the plant being cultivated. The size of the channelis also important. Configurations vary from 50-mm wide and 40-mm high to 300-mm wide and 70 mm high. For leafy vegetablesthe standard size is 150-mm wide by 70-mm high. The size of thechannel that is used will govern the type of plant that can becultivated. For most standard-size channels, plants that can begrown successfully include lettuce, endive, strawberry and manyMediterranean and Asian vegetables and herbs. Plants such astomatoes and cucumber, the so-called vine crops, are lesssuccessful owing to their large root structure, which can causechannel blockage and ‘ponding’, where the water is unable to flowfreely.

Channels or trays should have a slope of 1:30 to 1:50 to preventponding and water-logging, although this may still occur as plantroots mature. The slope can be provided by the floor, benches, racks,or the lay of the land.

As a general rule, flow rates for each channel should be around1 litre per minute. The rate may vary from installation to installation,but it should be at least half a litre per minute and no more than 2litres per minute. Flow rates outside these parameters can causenutritional problems.

There is no strict watering regime and irrigation cycles varyfrom one grower to another. While most NFT systems use acontinuous watering cycle, some growers prefer intermittent cycles,with a few minutes of irrigation every 10 to 20 minutes. Intermittentcycles increase aeration in the root zone, but on hot days there is afine line between good aeration and dry roots.

Reservoir volumeThe ideal volume of working nutrient solution in the reservoirdepends on the type of plant being cultivated and is critical to thesmooth and effective running of NFT. As a general rule, allowaround 1 litre of nutrient solution per plant; for example, if youare growing 20 plants, then the nutrient solution volume shouldbe around 20 litres. Less may cause plants to take up substantiallymore water than nutrients, and more may do the opposite,increasing or decreasing nutrient concentration over a shortperiod of time. An increase in nutrient concentration can causeroot injury, while a decrease will slow down plant growth. Also,

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A tiered NFT system to grow a variety ofleafy greens and herbs.

A DFT (Deep Flow Technique) system, a hybrid system that combines NFT andaeroponic principles.

Channel widthFor the healthy vine plants, such ascucumbers and tomatoes, narrowchannels can be dismissed. In soil,you can see vine crops produce largeroot systems. In hydroponic systemsit is no different. To grow vine crops,the channel needs to be at least 250mm wide at normal spacing toaccommodate the abundant rootmass. Such widths can beconstructed at ground level usingthick black and white plastic to formchannels.

Channel slopeThe NFT channel slope must be firmand regular to avoid ‘ponding’, whenplant roots lose contact with theatmosphere and show symptoms ofwater-logging.A minimum slope of 1:50 is widely

accepted; however, a slightly higherslope is more desirable. In practice, ahigher slope may be more difficult toachieve due to the extra lift requiredby the pump. There is no maximum slope, and

many successful crops have beengrown in vertical NFT systems. Theonly major obstacle to such systems isthe ability to firmly hold plants in thechannel.

A-frame NFT system

Growing bedsGrowing beds can be constructed at ground level or raised, althoughground level is les labour intensive. A typical ground bed shouldhave an approximate width of 1 metre and a depth of 400 mm. Theslope of the bed should be about 1:400 to allow for good drainage ofexcess nutrient solution. The growing bed should be filled to within20 mm of the top at the end near the nutrient or header tank andwithin 40 mm at the other end. If the growing bed is filled evenly, itwill cause uneven watering of plant roots.Ground beds can be constructed easily using wooden planks orconcrete reinforcement wire, bent at the sides and ends to form thegrowing bed. The bed should be lined with plastic, such asswimming pool or pond liner to prevent the nutrient solutionleaching into the bare ground. If you are using black polyethyleneplastic film, it should be doubled over for maximum strength – asingle layer of film will stretch and tend to mould around sharpobjects once the bed is filled with gravel and/or sand, which maycause it to rupture. A perforated, 90 mm drain pipe or ‘agpipe’should be set the entire length of the growing bed, which in turnshould be connected to a main pipe at one end to collect waste waterand to conduct it away from the growing area. If sand is used, thedrain pipe should be covered with blue metal to prevent cloggingand to help discourage plant roots from entering the pipe.

Nutrient reservoirThe nutrient reservoir should be watertight and hold a volume 30to 40% more than the total volume required to fill the growing bed.An automatic float valve connected to the refill line will handleautomatic refilling when required. Nutrient can be delivered eitherby gravity or by means of a submersible pump. Drain the reservoirperiodically and remove any sludge or sediment that hasaccumulated owing to impurities in the nutrient salts.

Irrigation linesFor small garden beds, a single 13-mm black polyethylene pipe canbe run down the length of the bed with spaghetti lines inserted every300 mm. For gravel systems, each plant will require a singlespaghetti line. Larger beds will require 13-mm poly pipe along theinside of each plant row, from which the spaghetti lines run.Emitters can be used to deliver nutrients to plants, adjusted todeliver 4 to 6 litres per hour. Alternatively, spaghetti lines can beinserted into the main 13-mm feed line. For sand culture systems, ashort length (50 mm) of 13-mm poly tube can be attached to the end

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Flood-and-drain systemFlood-and-drain systems are easy to construct and operate, andmay consist of flood-and-drain tables or trays, or a bucketarrangement. Both set-ups can be expanded as required, but theymust be designed to provide rapid fillings and draining. Toachieve this, the water inlet and outlet lines should be at least 19mm in diameter, alternatively, the inlet smaller than the outlet.A timer is needed to control the pump and the irrigation cycles.All storage tanks and delivery lines should be opaque to reducealgae growth.

Flood-and-drain tablesFlood-and-drain tables may consist of single or multiple trayspositioned at the same level, or terraced with each successive levellower than the one before it. The latter method is ideal for unevenground, or for gravity-feed systems. The bottom of the higher bedshould be level with the top of the lower bed.

Growing beds should have a minimum depth of 12 cm. Theoverflow valve should be set so that the table floods to within 10mm of the top of the substrate before it overflows back to thenutrient reservoir in the case of a single table, or into the next tablein the case of terraced tables or trays.

Nutrient reservoirIn the case of single or interconnecting multiple tables at the sameheight, the nutrient reservoir is positioned underneath the first table,and uses a submersible pump to distribute the nutrient solution. Forterraced tables or trays, the nutrient solution is stored in an above-ground header tank raised a metre or more above the level of thehighest growing bed. An automatic solenoid or manual gate valveis used to control the flow of solution. The nutrient solution flowsthrough the system and drains to a sump, from where it is pumpedback into the raised header tank.

Drip-irrigation systemYou can construct a simple drip-irrigation system using a growingtray, nutrient reservoir and trickle feeding system operated by apump on a timer. A typical drip-irrigation system uses rockwool,coco peat, gravel and/or sand, perlite/vermiculite mix, expandedclay or sawdust as a medium. Each of these substrates has its strongpoints, with the choice usually governed by the budget.

A typical flood-and-drain table is usedhere to trial different mediums forgrowing cinnamon basil.

Modular drip-irrigation system withexpanded clay medium. Nutriewnt flowsback to the nutrient reservoir using gravity.

Building tips• Building a hydroponic system, likeany other activity, can be a loteasier and more enjoyable if youhave the right tools andequipment. Think plumbing!

• When selecting a hydroponicsystem, the main considerationshould be maintenance time. Asmall recirculating system whichcan grow up to 50 plants requiresabout 10 minutes work each day;to check the pH and nutrient level,and to renew the nutrient solutionfrom time to time.

• Only plant what you are likely toneed during the harvest period. Ondeciding how much to plant,picture the harvest. If you can onlyuse four cabbages and six lettuceduring the 4-week harvest period,then plant only your requirement.If you are unsure of their possiblesuccess, add a few more for extrameasure, but never more than twiceas many as you want to harvest.

Environmental protectionClimate is one major variable youcan’t control. In a hydroponic gardenyou can modify or move your gardento improve the growing conditions. Itmay mean erecting a simple windscreen, adding a reflector to supplymore light, heating the growingmedium to speed up germination, orusing a variety of devices to protectplants from frost.

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of each spaghetti line to channel nutrients to each side of theirrigation point. Emitters, above ground pipes and fittings shouldbe black to prevent algae growth inside the irrigation system. Algaewill rob nutrients of oxygen and minerals in the presence of light.

Irrigation cycleThe irrigation system should be capable of delivering 6 to 10 litresof solution per minute. If a timer is used, it should be programmedto deliver nutrients two to five times daily, depending upon thematurity of plants, weather and seasonal factors. Once a week asample of the run-off should be taken and tested for total dissolvedsalts. If the dissolved salts reach 2000 parts per million (ppm), thenthe entire bed should be leached free of salts using fresh water or aweak nutrient solution.

Rockwool systemRockwool systems can be either free drainage or recirculatory.Because of the high water-holding capacity of this substrate, you canget away with feeding it less frequently than other media. However,it is good management practice to feed plants several times daily –the exact number depending on the crop being grown. Frequentirrigations are required just after transplanting. Then, as plantsbecome established, five to ten times daily should suffice, increasingto 20 times daily in summer. Irrigation should continue until 10% ofexcess nutrient solution drains from the slab.

Free drainageFor free drainage rockwool systems the best floor is of levelledconcrete, with a slight slope on each side inclined towards the centre.

This type of floor allows good drainage away from the slabs, goodlight reflection, and good hygiene. An adequate catchment areashould be provided to channel excess nutrients away from thegrowing area. Soil or sand floors are also suitable but should belevelled in the same manner, thoroughly disinfected and coveredwith thick white plastic sheeting to give good light reflection as wellas hygiene.

Rockwool beds should be spaced at 1 metre intervals to allowgood access between beds. The nutrient solution is delivered to thebase of each plant with mico-irrigation lines (2-4 mm), supplied froma rigid PVC pipe or 19-mm poly irrigation line running along eachbed and fed from a central nutrient reservoir.

RecirculationRockwool recirculatory systems are rapidly gaining popularityamong home gardeners. Using the same fundamental drip-irrigation techniques as for rockwool free drainage systems,recirculatory systems vary only in their configuration. They rangefrom slabs placed on raised trays with a 1:200 incline to allow theslabs to drain, to self-draining growth modules. In wither situationthe nutrient solution is captured and recirculated at regularintervals.

Aeroponic systemAeroponic systems can be easily constructed using 20-litre bucketsor a deep tray; a submersible pump; an air pump and an air stone;and spray nozzles. The spray nozzles must be positioned within thechamber so that at least a portion of each plant’s roots is sprayeddirectly. The nozzles may be left on at low pressure continuously oroperated intermittently, on for 1 minute and off for 2 minutes.

An A-frame aeroponic system can be constructed. This typeof design makes the most of available space and light. Each side ofthe panel should have a series of 50-mm holes drilled toaccommodate net-like pots with their seedlings. Additionally, theA-frame should be hinged so that each side of the panel can beraised to facilitate easy micro-irrigation and pump maintenance, andcleaning between crops.

Electrical pumpsIn hydroponics, pump choice is of fundamental importance and isdirectly related to the nature of your system, be it flood-and-drain,NFT, aeroponics or drip-irrigation. Pumps are basically divided intotwo types – positive displacement and rotodynamic. RotodynamicA typical recirculatory rockwool system.

Rockwool layoutThe layout for a recirculatoryrockwool system is fundamentallythe same as for a free-drainagerockwool system. It is necessary tocollect what would otherwise be thedrainage and to re-direct it back intothe supply side of the irrigationsystem.This can be achieved by setting

slabs into a polyethylene line gullyon the ground or by raising the slabsonto channels or benches fromwhich the run-off solution iscollected. In either case, the slope ofthe run should be regulated to give areasonable water-to-air ratio withinthe slabs.

A-frame aeroponic system. Each panel ispre-drilled with 50-mm holes to fit small

growing containers.

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pumps are further divided into three categories: centrifugal, mixedflow and axial flow.

In hydroponic systems the main types of pumps used arerotodynamic, and of these the centrifugal pump is most common.This is the most efficient pump for pumping large volumes withrelatively low lifts – precisely what is needed for most small-scalehydroponic systems. Centrifugal pumps do not actually encapsulatea volume of fluid in order to pump it, but rely on what is called‘hydrodynamic action’. The impeller is enclosed in a chamber calledthe volute, which has two openings: the inlet and the outlet. To thisis connected the motor, which drives the axle that the impeller sitson. Spinning action produced by the impeller forces water throughthe outlet, then draws it back in through the inlet. The centrifugalpump is designed so that it can drain back through itself. Thesepumps by their nature are not self-priming, so they should be eithersubmerged or placed in line – preferably below the reservoir.

The choice most buyers face is whether to use a submersibleor an open-air pump. Submersible pumps are the most popularbecause they are easy to install, quiet to operate and very efficient,and they require very few fittings. The only disadvantage is itsproximity to water nutrients and the casing and shaft must besealed against the possible ingress of solution. While the casing iseasy to seal, the shaft is more difficult. Also, nutrient salts areaggressive and can reduce seal life. Suitable pumps are constructedof ABS plastic and are filled with chemically resistant seals and nometallic parts.

Open-air pumps generally need fittings that are more precise

and more costly. Most either need to be primed or require that theinlet to the pump head be flooded. While this is easy when the pumpis running, starting the pump is in fact when the problem occurs.One way to overcome this is to install the pump well below thesolution level in the reservoir. Larger non-submersible pumps aregenerally much easier to fit.

An alternative to both submersible and non-submersible pumpsis an air lift system which uses a simple and inexpensive air pump.Properly rigged, the pumping system works by displacing water withair. The main disadvantage is that the solution is not moved underpressure and so cannot easily be distributed to several channels oroutlets. Accordingly, a separate air pump needs to be provided foreach irrigation outlet. Although it can be costly and complex, this low-cost pumping solution is ideal for systems that have a single irrigationpoint, such as a single-channel NFT unit. While the air-lift systemcannot be used for draining the reservoir, unless drainage by gravitycan be arranged, and it is susceptible to a falling solution level in thereservoir, its overriding advantage is that it introduces aeration intothe nutrient solution, thereby adding oxygen.

When designing an air-lift system, you should take care toensure maximum efficiency, resulting in fewer problems and loweroperating costs. This is achieved through uniformity of pipediameter, and a minimum of bends and fittings.

FiltersFilters are an essential component in any drip-irrigation system. In-line plastic filters should contain a fine mesh screen, which can beremoved and cleaned periodically. The filter should be installed in-line, soon after the submersible pump. Alternatively, or additionally,the pump can be placed in a filter bag, such as those available fromselected hydroponic stores. A nylon stocking will also serve as apractical filter bag substitute.

Cross-section of a typical centrifugal pump.

Electrical safetyElectrical safety is extremelyimportant in any poweredhydroponic system since water andelectricity are a lethal combination.Most systems require electricity onsite to drive appliances such aspumps and heaters and, whilesystems do not require any specialelectrical installation, the reality isthat the growing environment itselfdoes not favour electrical safety andthere is an increased risk of electricalshock from faulty supply orappliances. This is because thehydroponic environment tends tohave high humidity, and floorsurfaces may be damp. As such, anautomatic earth leakage detectorcircuit breaker should be installedfor use between the mains supplyand the electrical equipment.

Simple layout for an air-lift system.

Layout for non-submersible pump, ensuring a flooded inlet.

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Although large-scale commercial hydroponic systems mightappear daunting to the novice, they are really quite simplein construction and operation. Small-scale systems

designed along the same lines can be set up on a patio, a roof top,or in the backyard with very little effort. Plants grown in an outdoorsystem should be started during the season recommended fornormal soil gardens. However, where the environment can becontrolled in closed structures, crops can be grown year-round.

Hydroponic systems will not compensate for poor growingconditions such as inappropriate temperature, inadequate light orpest problems. Remember. Hydroponically grown plants have thesame general requirements as field-grown plants, the only majordifference being the method by which the plants are supported andsupplied with nutrients.

Seed germinationLarge seeds can be planted into aggregate culture systems or do-it-tourself propagators. To ensure a good stand, small seeds can besown in rockwool or a mixture of perlite and vermiculate. I havefound a mix ratio of 3:1 ideal for seed germination. Once they havedeveloped into healthy seedlings and ‘hardened’, they can betransplanted into the hydroponic system. With water culturemethods, plants must not be transplanted into the system until theyhave developed an adequate root structure.

Seeds can be sown in any growing media including sand,perlite, vermiculite, rockwool or coco peat. Wet the seeds and coverwith a wet paper towel, or cover the container with ‘Gladwrap’ tocreate a mini-greenhouse until they germinate. Alternatively, investin or manufacture your own mini-propagator. Once the seeds havegerminated, remove the cover and thin them. Use a dilute nutrientsolution rather than water to moisten the young seedlings asrequired because the germination medium is not designed toprovide nutrition. When the seedlings are large enough totransplant, gently wash any growing medium other than rockwoolfrom their roots, but do not be too concerned if fragments of themedium remain. Seedlings germinated in soil and purchased from

the local nursery can also be transferred to hydroponics. Simplywash the soil from the roots using tepid water, taking care not todamage the fine root hairs.

Seedlings to be transferred into most systems can be grownwith their roots exposed or in rockwool/coco peat cubes or plugs.If you want to transfer them to water culture or aeroponic systemsit is best to grow them with their roots protruding from the growingpot or rockwool/coco peat cubes or plugs. Seedlings destined forwater culture channel can be grown in rockwool cubes, coco peatplugs or qa compressed mixture of perlite and vermiculite. Thesesubstrates provide weight and help to support the seedlings in thechannel. The substrate also blocks light from the roots, preventingdamage and discouraging the formation of algae in the channel.

CloningThe practice of cloning, whereby one cell of a plant is isolated bymeans of a cutting and grows into another plant, is recognised asone of the most efficient and productive methods of plantpropagation in hydroponics. Whereas seeds are produced by sexualpropagation, cloning results in asexual or vegetative propagation.The resultant plant is genetically identical to the host from whichthe cutting came, provided it is grown in exactly the sameenvironment as the parent plant. Cuttings from the same plantgrown in different growing conditions will develop differentcharacteristics.

Cuttings can be taken from any plant, regardless of age orgrowth stage. However, cuttings taken from young vegetative-stageplants root and grow quickly, whereas cuttings from a plant inflower usually root a little more slowly.

Cloning is achieved simply by taking a cutting from a plant,dipping it into a rooting compound to minimise antimicrobialactivity, and placing it into a growing suitable growing mediadescribed earlier. Cuttings can be taken from anywhere from thehost plant but stems should be no thinner than 4 mm and no thickerthan 6 mm for best results. New cuttings should then be fed a half-strength nutrient solution.

Healthy cuttings will retain almost all their leaves; however,it is natural for some leaves to die off during the rooting process.The cuttings should develop a good root structure within 2 weeks.After the second week, cuttings should be fed full-strength nutrient.

Take care not to overwater or underwater new cuttings.Overwatering can cause roots to rot, and under-watering will causethem to dry out and shrivel. Healthy roots are thick, white and hairy

Planting

Seeds can be planted in speedling cells(above) or rockwool blocks (below), whichare then transplanted to the hydroponicsystem once the seeds have germinated.

A range of propagation powders and gelsare available from local nurseries and

hydroponic stores.

Cloning material should have the lowerleaves removed.

available for checking pH levels.The nutrient solution should be changed once every 2 weeks whenthe plants are small, and once a week as the plants begin to growrapidly. Add water daily to keep the amount of solution constant.These are basic growing practices that work for me, but may varyfrom one grower to another depending on their growingenvironment practical experience. Good practices includediscarding waste solution in a responsible manner. Nutrient-richwaste water can be diluted and re-used on fruiting and ornamentaltrees soil and garden beds with spectacular results. Commercialgrowers in closed systems seldom dump their nutrient solution,preferring to bleed 10% of the total volume at regular intervals. Inpoorly maintained channel systems, this practice takes care of it selfas a result of small leaks in the system.

TemperaturePlants grow well within a limited temperature range. Temperaturesthat are too high or too low will result in abnormal growth anddevelopment and reduced yields. Warm-season vegetables andmost flowers prefer a temperature range between 150C and 240C.Cold-season vegetables, such as lettuce and spinach, grow bestbetween 100C and 210C.

WaterProviding water to plants is not difficult in water culture systems,but it can be a problem in aggregate systems. During the hotsummer months a large tomato plant can use 2 litres of water perday. Therefore, aggregate systems need to be kept sufficiently moistto prevent plant roots from drying out and dying. If roots do dryout, the plants will recover slowly but production will be reducedeven when proper moisture levels have been restored.

Poor water quality can be a problem in hydroponic systems.Excessively alkaline or salt-laden water, such as bore water, canresult in a nutrient imbalance and poor plant growth. Softened watercan contain harmful amounts of sodium. Water that tests high insalts (300 ppm) or more on the TDS meter) should not be used as itwill cause a nutrient imbalance.

OxygenA key element to successful hydroponic growth is oxygen. Thisallows for respiration, and provides energy for water and nutrientuptake. In soil, oxygen is usually abundant, unless the soil iscompacted; but in hydroponics plants growing in water will quickly

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looking. Damaged roots are thin, yellowish or brown, and have littleor no root hairs. Once full strength nutrient is applied, it is a goodidea to start balancing the nutrient solution to about pH 6.0 to 6.5.

Once plants have developed adequate roots they should betransplanted to their hydroponic system and started on a regularfeeding regime. If using rockwool cubes or coco peat plugs, do notremove the media, but transplant direct into the growing system,albeit NFT, rockwool, coco peat, aggregate or aeroponic.

Transplanting from soilPlants can be transplanted from soil to a hydroponic system. Simplywash away excess soil in luke-warm water, taking care not todamage the fine root hairs. The success rate of transferring soil-grown plants to hydroponics may be lower for mature plants whichhave developed a large tap root, as this is easily damaged when theplant is removed from soil.

In hydroponics, plants develop a capillary-like root structurerather than large tap roots. This is because nutrients are readilyavailable and plants do not have to stretch out and search orcompete for available nutrients as they do in soil. Therefore, theyounger the plant, the more readily it will adapt to hydroponics.Plants with large, complex root structures will find it difficult toadapt to a hydroponic medium and will have a high mortality rate.It is far better to take a cutting from the plant for hydroponiccultivation.

Nutrient solutionsPremixed nutrient solutions are available from a number of sources,including the local nursery and specialist hydroponic stores locatedthroughout the major and regional centres of Australia and NewZealand. They can also be purchased on the internet from manyspecialist mail order businesses at a comparable cost. They arerelatively inexpensive and easy to use. As you become more familiarwith growing plants hydroponically, you might wish to make yourown nutrient solution. Again, the raw elements are available fromspecialist hydroponic outlets.

As plants take up nutrients, they release into the solutionchemicals or by-products that might make it more alkaline. Whenthe pH rises above 7.0, add small quantities of phosphoric acid ornitric acid to bring it back to a pH between 5.5 and 6.5. For largeplants it may be necessary to do this daily. If the solution becomesacidic, the pH can be raised again with potassium hydroxide (KOH).A variety of pH can meters and colourmetric testing kits are

For woody plants, cuttings should begreen-barked and not contain any of thewoodier-type bark, which indicates age.They should be 10-15 cm tall with three tofive sets of well-developed leaves and agrowing tip at the top.

Seedling and cloning shells can be easilymade using clear plastic or an oldaquarium.

When to transplantWhen seedlings are about 1-2 cmhigh or have their true leaves (thoseresembling the plant species, insteadof the ones known as ‘seed leaves’,which first appear), they have reachedthe proper stage for transplanting tothe hydroponic system.

Plants that are grown insheltered conditions are usually tootender to transplant directly into yoursystem. They must be ‘hardened off’;that is, gradually accustomed tooutdoor conditions to prevent theshock checking active growth.

OxygenPlants cannot live without oxygen.This vital element is obtainedthrough photosynthesis andrespiration. The roots of allhydroponically grown plants needoxygen for their life processes andfor best growth. When oxygen is cutoff from the roots by their constantimmersion in water or compaction ofthe substrate, roots will suffocateand die.

Heating pads are available in varioussizes to promote seed germination atoptimum temperatures

Plant supportIn a garden, plant roots are surrounded by soil, which supports thegrowing plant. In hydroponics, plants must be supported artificially,usually a trellis, which are available in many shapes and sizes, anA-frame structure, or wooden stakes. For large fruiting plants, suchas pumpkin, rockmelon and watermelon, some growers supportfruit using a hair net or nylon stocking.

For hydroponic ground beds, the simplest and mosteconomical support structure consists of two fence posts positionedat each end of the growing bed, with taut wire strung at differentlevels between them. In this way, plants and vines can be supportedat different stages of growth.

Another popular method of support is a high wire or cablerunning above the growing bed, from which plants are supportedusing string and specially designed spools and clamps. This methodis favoured for the cultural technique of ‘layering’, where sectionsof vines are defoliated after harvesting fruit then lowered. In thisway, plant life and fruiting season can be extended to some degree.The string should be tied to the support cable and spool directlyabove the plants, leaving up to 1 metre of extra length at the cableend in case you wish to carry the plants for a longer-than-normalgrowing period. They can then be lowered once they have grown ashigh as the cable. The clamps can be placed directly under leafpetioles, not above as such a position gives no support. Clampsshould not be placed under flower clusters as the weight of maturingfruit may later break off the cluster and fruit may be damaged bythe clamps. For plants such as tomato and cucumber, several clampswill be needed for each plant, positioned every 30 cm or so to giveadequate support as fruit matures.

exhaust the supply of dissolved oxygen. A common method ofsupplying oxygen is to use an air stone in the nutrient reservoir.

LightAll vegetable plants and many flowers require large amounts ofsunlight. Hydroponically grown vegetables, like those grown in agarden, need at least 8 to 10 hours of direct sunlight each day toproduce well. Most artificial lights are a poor substitute for directsunlight as they do not provide enough light intensity to producean economical crop. High-intensity discharge (HID) lights, such asmetal halide and high-pressure sodium lamps, can provide morethan 1,000 foot-candles of light, and for the serious home gardenerthese lights can be used successfully where sunlight is inadequate.However, the fixtures and lamps are expensive and may not beeconomically justifiable.

Plant spacingWhile it is true you can grow plants quite close together inhydroponics because they do not have to compete for availablenutrients, plant density is, nonetheless, a critical factor for optimisingyields. For example, for tomato and cucumber, the recommendedplant density is two to three plants per square metre. Plants can begrown closer together but the yield will suffer and the crop qualitywill be inferior to that of plants grown at the recommended plantdensity primarily to maximise light penetration. Plants spacedfurther apart also mean better air circulation.

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Plant spacingOvercrowded plants become tangledand block each other’s light,resulting in spindly, low-yield crops.The best guide to planting distance isexperience. A general rule of thumbfor large plants, such as cucumberand tomato, is to plant no more thanthree plants per square metre. Forlettuce, a spacing of 250-300 mm isadequate.

Tall plants can be supported by string from an overhead wire or cable.

The shortage of one element can also upset a plant’s ability toaccumulate one or more other elements, resulting in a simultaneousmineral deficiency and surplus. For example, a shortage of boroncan cause a calcium deficiency and a calcium deficiency can lead toa potassium deficiency, and vice versa. Because of these complexchain reactions it is extremely difficult to determine visually whichelements are responsible for which symptoms when early diagnosisis essential.

To increase the chance of recognising potential nutritionaldisorders, it is a good idea to plant alongside the main crop an ‘earlyindicator’ plant – one that is susceptible to various nutritionaldisorders. For example, if the main crop is tomato, plant apassionfruit, cucumber or lettuce as well, as these plants are verysusceptible, respectively, to boron, calcium and magnesiumdeficiencies. Such early warnings will enable you to adjust thenutrient solution in order to prevent a deficiency in the main crop.Also, a weak tomato plant will show deficiency symptoms before astrong plant, acting as a further warning.

Overall, every possible tactic should be employed to give earlywarning of nutritional disorders, since such maladies will lead toyield reductions, poor quality fruit, and eventually plant death.

Generally, nutritional disorders appear simultaneously on allplants of one crop and from the bottom leaves up. (If a disorder isnon-nutritional – that is, caused by pests and diseases – symptomsbegin on a few plants and progress to neighbouring ones.)

Environmental problemsSymptoms of distress in plants can sometimes be caused byenvironmental problems. The possibility of nutritional problemsmust therefore be considered in relation to all the conditions inwhich the plants are growing, and not merely in terms of theelements in the nutrient solution. For example, plants will not growto their optimum capacity if the temperature is too low and may beinjured if it is too high. Similarly, light is obviously important; plantswill not grow well in insufficient light. The humidity of theatmosphere has a significant effect on plant growth, as water lossfrom the leaves is a major factor in balancing the plant’s moisturerequirements.

The problems of such influences in the plant environment arecomplicated by the fact that, rather than act independently, theymodify one another. A plant’s need for different elements can beaffected by conditions of light, temperature and water supply,among other environmental factors. For example, a plant will

Nutritional disorders in hydroponics are caused by adeficiency or excess of at least one mineral element. Effectedplants exhibit symptoms specific to the culprit element

Mineral elements are classified as either mobile or immobile,and some are both. Mobile elements include nitrogen, potassium,phosphorus, magnesium and zinc. These can all move from theiroriginal site (older leaves) to the actively growing region of the plant(younger leaves). So, the first symptoms of a nutritional disorderwill occur on the older leaves and on the lower part of the plant.Immobile elements include sulphur, calcium, iron, boron, copperand manganese. They cannot be translocated to the growing regionon their own, and so remain in the older leaves where they wereoriginally deposited. Any deficiencies of these minerals will,therefore, first appear on the upper, younger leaves and developingfruit load.

It is important for nutritional disorders to be recognised early;the longer a disorder continues, the faster it will spread to otherareas of the plant, eventually killing plant tissue. Also, the longer anutritional disorder continues, the more general the symptomsbecome and the more difficult it is to identify the disorder. Generalsymptoms are yellowing (chlorosis) and browning (necrosis) ofplant tissue.

Toxic effects in plants can be produced by both essentialelements and non-essential, or trace elements (those found in water,such as sodium, chlorine and chromium). An oversupply of essentialelements is much less toxic than an oversupply of trace elements. Infact, there is a fair safety margin for excess major elements, whereastrace elements need to be precisely monitored.

An excess of one element can lead to a deficiency of another,which ultimately results in a deranged metabolism. For example,excess nitrogen or phosphorus might result in insufficientpotassium; and excess potassium might lead to a deficiency ofmagnesium or calcium. This type of injury applies particularly toessential nutrients.

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Nutritional andenvironmentaldisorders

Potassium deficiencyA potassium deficiency can berecognised by dead areas on leaves.Excess potassium can causemagnesium deficiency and evenmanganese, zinc or iron deficiencies.

Phosphorus deficiencyA phosphorus deficiency stuntsplants, and often turns them darkgreen. Maturity is often delayed.

Nitrogen deficiencyA nitrogen deficiency restricts growthand plants are generally yellow,especially on older leaves. Youngerleaves may remain green while stems,petioles and lower leaf surfaces turnpurple.

Tip burnTip burn can be attributed to acalcium deficiency and hightemperatures.

probably need less nitrogen but more potassium under conditionsof relatively low light intensity, a fact of some significance fortomatoes grown in a glasshouse. The relationship betweennitrogen and light can be demonstrated by growing a plant undernormal light conditions with insufficient nitrogen: the leaves willshow the well-known symptom of a nitrogen deficiency – a palegreen, yellowish colour with orange and red tints. If such a plantis then shaded the leaves will turn a darker green and growth willincrease visibly.

Similarly, the rate of water absorption is less at lowtemperatures than at higher temperatures, and efficient intake alsodepends on good aeration. These facts can cause a water deficit inplants growing in cold conditions when the air temperature is high.

When plants are grown in an unsuitable environment,including one of inappropriate nutrition, they react in specific ways.Thus, if there is insufficient light, leaves will lack green colouringand might even tend towards white. Plants might be spindly andstrained. If the temperature is too high, growth may be restricted,the tissue woody, and the leaves a bluish colour.

Remedial actionDeficiencies or excesses of mineral elements show in a number ofways: in colour, density, size and shape of leaves; in the thicknessand colour of stems and the length of internodes; in the colour,fibrousness and thickness of roots; in the abundance and timing offlowers; and in the size, colour, hardness and flavour of fruit.Recognising those particular effects is the key to diagnosingnutritional disorders.

When you recognise, or even suspect a nutritional disorder,the first step is to replace the nutrient solution with a fresh solution.If you have identified a malady as a nutrient deficiency, apply anappropriate foliar spray for a rapid remedial response, but takecare not to burn plants by using too high a concentration ofnutrients. It is best to foliar feed a few plants first to observe theresults over several days before treating the whole crop. There maybe a 7 to 10-day wait for an obvious response to a control orremedial measure.

In the event of nutrient excess (or toxicity), flush the mediumwith a fresh batch of nutrient solution to reduce residual salt levels.This may be necessary several times over a week or so, dependingon the severity of the disorder. Do not use plain water to flush themedium; flushing with fresh water can shock plant membranes andstarve plants of essential elements.

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ABOVE: Phosphorus deficiency in strawberry plants. The‘gooseberry-foliage’ effect is indicated by dull purple tints onthe leaves, which turn red as the deficiency becomes moresevere.

BELOW: The fungus Botrytis cinerea, also known as greymould, is a serious pathogen of rose blooms and other cutflowers.

ABOVE: Iron deficiency is evident in this cucumber crop.

Calcium deficiency manifests it self as blossom end-rot intomatoes (above) and tip burn in lettuce (below).

BELOW: Pythium rot in a cucumber crop. The diseasedcrown turns orange-brown in colour, often with a soft rotat the base.

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Deficiency symptomsWhile symptoms vary from plant to plant, the general symptomsof nutrient deficiencies can be listed as follows:

ELEMENT SYMPTOMSNitrogen Chlorosis (yellowing) of the whole plant, often with

reddening. The older leaves are usually affected first. Phosphorus Dark green foliage, reddening or purpling of leaves

or petioles.Potassium Older leaves might show necrotic spots or marginal

burn. Younger leaves may develop red pigmentation orbecome interveinally chlorotic and show a shiny surface..

Sulphur Chlorosis of the whole plant. The younger leaves are often affected first.

Magnesium Marginal or interveinal chlorosis, often quite strongly coloured. Green area of the leaf may form an ‘arrowhead’ in woody plants. Strong reddening may border the chlorotic zone, usually on older tissue first. Leaf tips and margins are often turned or cupped upwards.

Calcium The growing point dies. In fruit crops specific disorders are unique to individual fruits; for example, bitter pit in pome fruit, and blossom-end rot (BER) in tomatoes and capsicums (peppers). In leaf crops, such as lettuce, tip burn can be seen.

Iron Interveinal chlorosis. In severe cases total bleaching of young foliage is visible, followed by necrosis. Symptomsoccur on young leaves first.

Chlorine Chlorosis followed by necrosis evident with wilting leaves. Leaf tip and margin burn can also occur. Roots may appear stunted and tend to thicken near the tips.

Manganese Interveinal chlorosis. When the condition is severe, necrotic spots or streaks may form. Initially, such symptoms often occur in middle leaves.

Boron Death of growing points. Auxiliary buds may burst, giving a witch’s-broom appearance. Some species, such as grape, may show leaf distortion. Fruit may be distortedor show woody pits or cracking of the surface. Petiole cracking in celery and hollowness in some toot vegetablespecies are also apparent.

Zinc Symptoms include small leaves and rosetting. In less severe cases, chlorotic mottle is apparent.

Copper Death of young leaves. Other symptoms include chlorosisand failure of fertilisation and fruit set. (S-shaped shoot growth and fruit gumming is apparent in citrus.)

Molybdenum In legumes, general pallor is apparent. In non-legumes amottled pale appearance is evident. In mature leaves thereis marginal burn (rockmelon, maize and sunflowers). Whiptail is apparent in cauliflowers.

Toxicity symptomsSymptoms of toxicities are generally apparent in the older leavesof plants. Many toxicities produce chlorosis and necrosis of themargins and tips. (Symptoms are also given for fluorine andaluminium since these elements are often found in watersupplies.)

ELEMENT SYMPTOMSNitrogen Edge burn may be followed by interveinal collapse. The(Nitrate) root system is also restricted. In the case of ammonium-

nitrogen, there is initial chlorosis, and blackening around tips and edges of leaves, and roots may die.

Phosphorus Interveinal chlorosis is evident in younger leaves and can resemble an iron deficiency. Necrosis and tip die-back may follow in susceptible plant species. Marginalscorching and shedding of older leaves.

Potassium Symptoms may seem similar to those of magnesium deficiency. Possible manganese, zinc and iron deficiency.

Sulphur A reduction in growth and leaf size. Occasional interveinal chlorosis or leaf burning.

Magnesium No visible symptoms have been noted.Calcium No consistent visible symptoms have neen noted.Iron Sometimes brown spots are apparent.Chlorine Bronzing, chlorosis and marginal burn. Leaf drop may be

premature. In some plants the marginal burn is accompanied by upward cupping or curling.

Manganese Chlorosis, beginning at the leaf edge of older leaves, sometimes with an upward cupping. Interveinal bronze-yellow chlorosis in beans; orange-yellow marginal and interveinal chlorosis in lemons; brown tar spots in orange leaves; and necrosis in apple bark.

Boron Interveinal necrosis, often spotty at first.Zinc Excess zinc produces iron chlorosis in plants.Copper Reduced growth followed by symptoms for iron chlorosis.

Stunting and reduced branching are sometimes apparent.Molybdenum Symptoms are rarely observed. Tomato leaves turn golden

yellow. Cauliflower seedlings turn bright purple.Fluorine Scorching of leaf tip and margin, extending into interveinal

areas.Aluminium Symptoms in shoots are frequently similar to those for

phosphorus deficiency, indicating an impairment of phosphorus absorption and metabolism by high levels of aluminium. Roots grown in high levels of aluminium are frequently short, with many short laterals. Root tips are commonly brown.

it’ under certain conditions. If an infected plant is allowed to stayin the system, the virus may be carried from plant to plant. Thedisease can only be eliminated by removing and destroying theinfected plant.

The most recognisable symptom of viral diseases isdeformity, stunting and dwarfing and leaves often show the firstsymptoms. In vegetable plants the most common symptom is achange in colour. Leaves might show spots, streaks, blotches, orrings of light-green, yellow, brown or black. The leaves can alsochange their shape or size, sometimes puckering or developingrolled margins. Flowers will appear dwarfed, deformed, streakedor faded, even changing into leafy structures. These are only a fewof the symptoms of viral infections.

Viral infections are generally not transmitted through seeds.However, a plant can suffer serious loss if a virus is transmitted toseedlings early and spreads efficiently. While viruses can spreadunaided from cell to cell in one plant, they require assistance to passfrom one plant to another. A virus usually spreads as a result ofinsects feeding on an infected plant then a healthy one. It can alsobe transmitted by grafting and sometimes by secateurs that havebeen used on an infected plant, which is why it is so important tokeep such tools clean.

BacteriaBacteria are single-cell micro-organisms that are difficult to control.Although a few bactericides are available, control is primarilythrough prevention and elimination of infected plants. Some of themore common bacterial diseases include bacterial wilt(Pseudomonas caryophylli), known to affect carnations; bacterialblight (Xanthomonas pelargoni), also known as stem rot and leafspot on pelargoniums; soft rot (Erwinia chrysanthemi) of cuttingsand bulbs; bacterial leaf spots (Xanthormonas hederae), common ongeraniums and English ivy; and crown gall (Agrobacteriumtumefasciens), which infects roses, chrysanthemums and geraniums.

FungiFungal diseases are the most common of the four groups and havebeen the downfall of many a home gardener. However, they are theeasiest to diagnose and lend themselves to control measures.Fungi are much more complex than bacteria, being multi-cellularorganisms often consisting of several tissues. Most fungi reproduceasexually by the formation of spores. The most easily recognisedfungus is powdery mildew, characterised by a whitish powder on

Disease controlInfectious diseases can be the nemesis of any gardener. Many cannotbe eradicated and at best can only be contained, so prevention playsan important role. While disease problems are rarer in hydroponicsthan in soil gardening, diseases still pose a serious threat to plants ifallowed to go uncontrolled. With ever-increasing awareness of thedangers of chemical treatments, home gardeners should thereforemaintain a strict sanitation programme to prevent and control thespread of diseases.

Even with the best preventative programme, disease organismscan still get a foothold in any hydroponic crop. Such pathogens canbe transmitted from the bottom of a seedling tray or pot via water,or they may simply appear on purchased seedlings or cuttings. Whilesome rely on the moisture of the plant foliage to develop, others needa very wet root medium. Some diseases, such as the rusts andBotrytis produce wind-borne spores that can be transported throughthe air from host plants near or far.

Hydroponic gardeners should check their plants daily fordisease so that early identification can be made and controlsimplemented.

The diseases that afflict plants are caused by four groups oforganisms – viruses, bacteria, fungi and nematodes. In order tocontrol pathogens it is important to understand the characteristicsand life cycles of each of these.

VirusesViruses are minute organisms that live within plant and animal cellsand cause numerous abnormalities. Plants do not produce anti-bodies, which mean that they neither recover from a virus infectionnor develop immunity, although resistance to some viruses can bebred into plant varieties.

No pesticides are available to combat viral diseases; once aplant becomes infected it will remain infected for life, even thoughthe symptoms may become masked or the plant may ‘grow out of

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Managing pestsand diseases

Pests and diseasesIn hydroponics, soil-borne pests anddiseases are virtually eliminated.Nonetheless, plants grown insoilless culture are still susceptibleto certain common pests anddiseases. Vigilance and earlyidentification are important incontrolling such problems. The keyto a healthy garden is cleanliness,favourable environmentalconditions and cultural practices.

Bacteria preventionThe best prevention for bacteria is toeliminate infected plants and tosterilise pots, containers, and channeland irrigation equipment. Betweencrops, systems should be thoroughlycleaned using a mild solution ofchlorine, which is commonlyavailable as household bleach(sodium-hypochlorite). After cleaningthe system should be thoroughlyflushed with fresh water beforereplanting.

Fungus preventionThe best control against fungus isproper sanitation, disposing ofdiseased plants and using resistantplant varieties. Among the leastharmful chemicals that can be usedin combating fungi are sulphur andcopper. Sulphur is considered theleast objectionable among organicand hydroponic gardeners.

favoured by high temperatures, but this is not always so.Thielaviopsis causes a drier lesion than Rhizoctonia, but one that soonturns black because of the large number of black spores produced bythe fungus in the lesion. The disease does not occur in pH conditionsbetween pH 4.5 and 5.0. Colletotrichum is often associated with rootdecay in NFT systems and can invade healthy tissue.

Preventative measures are the same for all root-rot diseases.The most effective controls are the use of well-drained mediums;thorough disinfection or pasteurisation of the medium, andsterilisation of installations including seedling trays, pots, tools andbenches; clean plants; and a sound sanitation programme.

Verticillium diseases affect a wide variety of ornamentalplants, including chrysanthemums, snapdragons, roses, geraniumsand begonias. Symptoms vary with the host. With chrysanthemums,marginal wilting of the leaves usually occurs, followed by chlorosis,browning of the leaves and eventually death. Symptoms occur onlyafter blossoms buds have formed. Snapdragons can seem completelyhealthy until blossoms appear, at which time the foliage suddenlywilts. Rose buds tend to turn blue and fail to open, and leaves andstem tissue become mottled before the leaves fall and stem dies. Inthe case of begonias, yellowing usually occurs on leaf margins, butthe most distinctive symptom is the development of an extremelyshiny lower leaf surface.

Like other preventative measures for fungi, installations andimplements should be sterilised between crops, and cuttings orseedlings should be purchased from reliable nurseries. Verticillium,however, is seldom a problem in well-run hydroponic systems.

NematodesNematodes, also known as eelworms, are parasites that live in soiland hydroponic substrates, freshwater and on plants. They arebilaterally symmetrical, elongated, usually tapered at both ends, andalmost invisible to the unaided eye. Most nematodes are not harmfuland contribute to the ecological balance of soil. However, a few areharmful, especially when large populations occur, resulting in plantinjuries. The most effective means of eradicating nematodes is bypasteurising the hydroponic medium and sterilising all equipment.Harmful nematodes can be grouped into two broad categories –those that feed on roots, and those that feed on buds and leaves. Rootknot nematodes are among the most plant-damaging types. Infectedplants usually appear stunted and tend to wilt on warmer days. Rootgalls are generally conspicuous and easily recognised. However, thepresence of galls does not necessarily lead to plant losses. With

the surface of leaves, stems and sometimes petals. Mildew sporesare easily detached from the plants and carried along by the windto surrounding plants where they initiate new infections.High humidity is conducive to this fungus development, soventilation and heating in backyard greenhouses should be adjustedto avoid high humidity conditions.

To control mildew, grow resistant varieties and use fungicides,both outdoors and indoors. Although recommendations change,fungicides containing sulphur will always be on the list. Dustingsulphurs can be applied quickly and easily. As a preventativemeasure, plants should be treated with sulphur powders or spraysat regular intervals. But beware of sulphur in summer and undergreenhouse conditions as it causes defoliation under hightemperatures.

Botrytis (Botrytis cinerea) is a common grey-mould funguswhich attacks a variety of ornamental and vegetable plants, causingmore losses than any other single pathogen. The fungus attacksstems and petals on carnations, chrysanthemums, roses, azaleas andgeraniums. It is usually identified by the development of fuzzy,greyish spore masses over the surface of the rotted tissues, althoughsuch spores will not develop under dry conditions. Spores arereadily dislodged and carried by the wind to new plants. However,the spores will germinate and produce new infections only when incontact with water, whether from splashing, condensation orexudation, and then only on petals or injured tissue.

Again, high humidity favours Botrytis and should becountered with adequate ventilation to prevent spore production.In greenhouse or indoor environments avoid splashing andcondensation on plant surfaces. Because the fungus readily attacksold or dead tissue, and produces large quantities of air-borne spores,strict sanitation cannot be over-emphasised. Fungicides can be usedto control the disease, although a high degree of control withoutmodification to the environment is difficult.

Root rot diseases such as Rhizoctonia and Pythium not onlycause damping off of seedlings but, together with Thielaviopsis andColletotrichum, cause root and basal stem rot of older plants. Thesefungi are common and attack a wide range of plants. Both spreadby mechanical transfer of mycelium or spores in infested media,plant tissue and nutrient solutions.

Symptoms of Pythium are a wet rot that makes roots lookhollow and collapsed. It is favoured by cool, wet conditions.Rhizoctonia causes a drier brown rot and is favoured by anintermediate range of moisture, neither too wet nor too dry. It is also

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Nematode preventionThe best control for nematodes is todiscard infected plants and sterilisethe substrate before replanting. If indoubt, discard and replace thesubstrate.

wind-blown spores and insects to be unable to make their way backto your plants. Never throw plant debris on the floor during pruningas pathogens can easily spread to other plants. Rather, make a slothpouch that can be carried around the waist. Always make the effortto ‘go the extra yard’ for disease prevention. Devise a system thatfollows sound principles of sanitation without causing too muchextra effort.

Finally, when purchasing plant stock from a nursery, you aredepending on the sanitation programme of that business. Selectyour plant sources carefully and inspect each plant for anomalies.If propagating your own stock, maintain a careful diseaseprevention programme. Inspect plants regularly, use only cleanimplements when taking cuttings, and transport plant material inclean container.

Pest controlInsects, mites and other related animal pests pose an ever-increasingthreat to the quality of hydroponic crops. A careful plan ofprevention and control should therefore be maintained. While anumber of effective chemical sprays are available to combat insectinfestations, hydroponic hardeners tend to ignore these inpreference to biological and organic controls. After all, usingchemical sprays defeats many gardeners’ purpose in adoptinghydroponic techniques in the first place.

Eradicating pests by using chemical sprays can also haveserious consequences for the ecosystem. Although many of uswould prefer to have no insects in our gardens, the inescapable truthis that we need them to maintain the ecological balance. While ‘bad’bugs can wreak havoc, there are also many ‘good’ insects in thegarden, and chemical sprays are not discerning in what theyeradicate. In the normal scheme of things, the good and bad bugsbalance each other in the food chain. However, insect populationscan get out of balance occasionally, and we do need to take somekind of control action. Such action does not mean elimination oreradication, but rather reducing infestations within a tolerable limit.

Insects can be brought into the garden in a variety of ways:plant stock purchased from the local nursery being a common entrypoint. Such plants should be inspected carefully for insects and, ifaffected, should not be brought into your garden. Insects can alsobe attracted from neighbouring gardens by scents or simply carriedin by the wind. It is inevitable that insects are going to get into yourgarden, but if the harmful bugs can be detected early, they can becontrolled before any significant damage is done.

adequate nutrients, infected plants will continue to grow well andproduce almost normally.

Plants infected with root nematodes should be removed anddiscarded so that nematodes don’t spread. Thoroughly pasteuriseor replace mediums and installations before planting the next crop.

Leaf and bud nematodes can cause leaf and fruit distortion onmany ornamentals and strawberries. Leaf nematodes cause leafspots and defoliation. Yellow or brown spots appear first on thelower leaves, which eventually turn black. With favourabletemperature and moisture conditions, the spotting spreads untilmost of the leaf is destroyed. Leaf nematodes can be effectivelycontrolled by soft chemicals applied to the foliage.

Disease preventionDisease can be prevented by means of a total programme ofsanitation. Diseases caused by organisms such as Botrytis need ‘free’water on the plant surface for spores to germinate. Free water oftenoccurs as condensation, with warm air holding more moisture thancold air. During warm days the air picks up more moisture, and atnight the air cools and its moisture capacity drops until the dewpoint is reached and water begins to condense on any solid surface.

In a greenhouse environment, condensation can becontrolled by three methods: adequate ventilation (or exhaust fansat a low capacity), circulating air around the closed environmentwith the use of an oscillating fan, or totally extracting the air atregular intervals.

Mildew is also encouraged by high humidity. This can becontrolled to some degree by ventilating at regular intervals andmaintaining good air circulation. Humidity can be further reducedby watering early in the day when warm air can absorb moisturefrom wet surfaces.

Root rot and dampening-off diseases are conveyed bymechanical transfer of the fungus into the root media. Automaticwatering helps to prevent this occurrence because it minimises thesplashing that can occur during hand-watering. Good drainage ofthe medium also helps since infection by many pathogens isenhanced by high root-medium moisture levels. It is essential toavoid water-logging of the root zone at any stage.

Other control measures include sterilising trays, pots and othercontainers before they come into contact with a clean medium. Tools,plastic supports and watering systems should also be sterilised.Ensure that plant debris is removed and safely disposed of. Disposalpoints should be sealed and far enough away for micro-organisms,

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Disease prevention• Purchase disease-free plants fromreputable nurseries.

• Periodically clean equipment andimplements.

• Inspect plants regularly for diseasesymptoms.

• Remove all plant debris from thegrowing area.

• Maintain proper watering practicesto minimise ‘free’ water on plants.

Insect controlInsect free hydroponic gardensdepend upon creating a balanceamong the insect population. Ideally,beneficial predators and parasiteskeep the numbers of potential pestsat a low, tolerable level, thereforemaking sprays, dusts and trapsunnecessary.

Preventing insect problemsThere is much you can do to preventproblems with insects. Healthy plantscan withstand infestations better thanweak plants. A well-balanced diet ofnutrients will help to maintainhealthy plants.Plants need nitrogen, but an

overdose has been found to makeplants overly succulent and thereforeencourage various sucking insects. Itis best to make nitrogen available toplants slowly, by using a well-balanced hydroponic nutrientsolution.

hatches. The parasite works by laying an egg inside the whiteflyeggs, so that another parasite hatches out instead of a whitefly.Another natural control is the use of yellow sticky traps. Whitefly isattracted to the colour yellow.

AphidsAphids are a serious threat to all gardens. What you notice firstare leaves that are curled, puckered and discoloured. On closerinspection dense colonies of tiny, soft-bodied, pear-shapedinsects can be seen, especially on the tender growing tips andunderneath leaves.

Compared to most insects, aphids move quite slowly whendisturbed. They come in almost any colour and feed by sucking onplant juices. While that in itself is serious, the most serious threat isthe diseases they carry. Aphids also produce shinny honeydew,which accumulates into a choking mould. Combine these problemswith the fact that aphids are born already pregnant, they’re allfemale, and they reach adulthood in 1 week, and you realise why anaphid strike can be devastating. The natural controls against aphidsare ladybirds and green lacewings. Between these two good bugs,aphid control is usually quite successful.

Ways to control insect pestsThe two non-chemical means of insect prevention and control arebiological and organic. Biological control simply means using livingorganisms that feed on other insects; hand-picking; or companionplanting, whereby one plant protects another because of the odoursit emits, or the taste of its foliage. Commercial growers use anadaptation of this concept, introducing ‘banker’ plants into thegreenhouse that attract specific pests. Other biological controls canbe microbial – organisms that make insects sick – or parasites thatfeed on insects from the inside.

Organic control means the use of non-chemical concoctions,usually made from recipes handed down from one generation toanother. Other organic controls include crop rotation to disrupt aninsect’s habitat and hence breeding cycle, and the use of simple-yet-effective sticky traps.

Natural predatorsFor many home gardeners natural predators are the first line ofdefence. The main natural predators are ladybird (Crytolaermusmontrouzieri), praying mantis (Tenodera sinensis), lacewing (Chrysopacarnea), predatory mite (Phytoseiulus persimilis), parasitic wasps

Insects usually establish themselves in a particular location,perhaps a warm temperature zone or a wind-sheltered area, andexhibit particular plant preferences. When doing the rounds of thegarden you should identify such areas and plants and inspect themregularly with particular emphasis on the undersides of leaves.Some insects, such as slugs and snails, will hide in damp and darkspaces, or attach themselves to the underside of leaves on the surfaceof the medium, coming out at night to feed on the upper plant. Onemust be aware of these hiding places and know the signs of the pest.

Spider mitesAlso known as two-spotted mites and red spider mites, spider mitesare the bane of many a home gardener. This tiny pest is virtuallyinvisible to the naked eye and is identifiable only by the damagethey do. Early symptoms of its presence can be seen when plantsstart showing little yellow pin-size brown- to red-coloured speckleson the leaf surface. If you look on the underside of the leaf you maysee very tiny, oval-shaped mites scurrying about. A fine web overthe plat tops is another early warning indicator and this can berevealed by spraying plant tops with a fine mist of water – thedroplets cling to the web. In spite of efforts to rid the garden ofspider mite, they can be transmitted on clothes or just float in onwind currents.

Spider mites are most prevalent during hot, dry months, andespecially in hot, dry indoor environments. During the wintermonths they stop feeding and reproducing and crawl off toprotected nooks and crannies where they hibernate until spring.Each generation takes about two weeks from egg to adult. Attemperatures below 100C they become dormant, and at temperaturesabove 290C their life cycle accelerates. Since they dislike wetconditions, raising the humidity level in controlled environments isbeneficial. For outdoor gardens, plants should be sprayed withwater regularly.

WhiteflyWhitefly is a common pest and is easily recognised by its waxywhite, moth-like appearance. With a wingspan of about 3 mm,whitefly is usually found on the undersides of leaves where theysuck sap from the plant. When disturbed colonies of whitefly willrush out in the air, hesitate a while, then fly back into the foliage.Heavily infested plants will yellow and grow poorly.

For heavy whitefly infestations the most effective control is awhitefly parasite (Encarsia Formosa), which kills the pest before it

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Biological controlIf a crop is endangered despite yourprecautions, first consider biologicalcontrols. While most gardeners arefamiliar with the predaceous ladybugand praying mantis, many lesserknown beneficial insects and evenpathogens deserve recognition aseffective natural controls.

The most effective control for whitefly(ABOVE) is the parasite Encarsiaformosa (TOP), which kill the pestbefore it hatches.

Parasitic waspsA number of parasitic wasps in Australia play a predatory role –amongst them the true wasp, digger wasp, chalcid wasp and aphidwasp, which are of interest to home gardeners. Through the eyes ofa magnifying lens they look like fantastic creatures from aHollywood sci-fi film set, but they are real. The aphid wasp is verysmall (3-5 mm long) and brown or black. It is an important parasiteof aphids, scale insects and mealy bugs. The chalcid wasp will layeggs in the eggs of other insects. When the larval wasp hatches iteats the tissue of its host. These wasps can be recognised by theirbeautiful blue-green metallic-coloured bodies. They are among thesmallest of all insects and can be easily recognised because they haveno ‘waist’ between thorax and abdomen.

Predatory miteAlso known as the Chilean mite, the predatory mite has been usedto control spider mite in a wide range of greenhouse and outdoorcrops in Australia and overseas. It is an extremely voracious andeffective predator, and quite often completely eliminates thepopulation of the pest it consumes.

Organic optionsOrganic options for pest control include insecticidal soaps, whichcreate a very thin film on plant leaves and block the fine tubes thatall insects breathe through. However, the soap has no other effectand regular treatment is required. For best results, spray insecticidalsoap directly onto insects and to cover the undersides of leavesthoroughly. Since soap sprays can also adversely affect good bugs,it is best to use this strategy as spot spraying. These soaps are mildand will not burn plants.

Another effective organic control is kelp, used as a foliar spray.Available in powdered form, kelp is providing effective control againsta wide range of insects, but particularly red spider mite. Kelp is notonly harmless but also beneficial to plant health. The only disadvantageis that it can stain plant foliage if used in too high concentration.

(Leptornastix dactylopii), and scale insect predators (Chiloocoruslophanthae, C. circumdatus and C. baileyii).

Some of these biological controls can be purchased fromspecialist hydroponic outlets, or collected from surroundingbushlands and gardens and transported back to your garden. Youdon’t have to worry about these insects becoming pests themselvesas they are carnivorous (they do not like plants) and they can’t harmpeople or pets in any way. Most are so small that you are hardlyaware of them, and when the pest populations die off, they move onor die, too.

LadybirdsLadybirds are predatory, both as adults and as larvae. They prey ona variety of pests such as aphid, scale insects, mealy bug, thrips,small caterpillars and mites. The black ladybug (Cryptolaermusmontrouzeri) is of Australian origin and one of the oldest and mostsuccessful biological controls. In the early 1990’s it was used to savethe southern Californian citrus crop from mealy bug. It has a largeappetite and one to four ladybirds are enough for one infested plant.The ladybird eats not only mealy bug, but aphid and scale.

Praying mantisPraying mantis (Tenodera sinensis) are long, narrow, carnivorousinsects found throughout Australia. Their name stems from theirhabit of sitting motionless with their forelegs raised and heldtogether as though they were praying. In fact, they are more likelyto be waiting for their prey!

Praying mantis eggs are attached to vegetation and arevariable in form. Each species produces a characteristically shapedootheca, which looks like a small barrel with a lid. Mantis is amongthe most popular pest controls and a garden ‘fun pet’. They are veryinteresting to watch and can even be enticed to eat bits of food.

Lacewing larvaeLacewing larvae are ‘walking garbage bins’, eating a vast variety ofinsects smaller than themselves, as well as each other. Sometimesknown as ‘aphid-lions’, they can consume 500 to 2000 aphids orother pests during their 3-6 week life.

Lacewing eggs are laid on the tip of individual stalks of stiffsilk. Adult lacewings often fly to lighted windows or bulbs. If youare careful, they can be collected in a container and transferredto the garden. Specimens should be kept apart as they might eateach other.

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Predator Pest controlledLadybird Aphid, mealy bug, citrus mealy

bug, mealy bug eggs.Praying mantis Most insectsLacewing Aphid, citrus mealy bug, spider

miteParasitic wasp Citrus mealy bugPredatory wasp Spider mite

Praying mantis consumes many gardeninsect pests.

Lacewing eggs are usually found under aleaf, attached to stalks by stiff silk.

Lacewing not only look beautiful, but areextremely helpful in the garden.

Ladybirds eat large numbers of aphids.

PestOil controls citrus leaf miner, scales,mites, mealybug, aphids and white fly on

citrus, grapes, fruit trees, roses andornamentals.

experience is that algae are not harmful to plants, except on rareoccasions in stagnant water when it can harbour insects anddiseases. Some growers believe algae gives off certain enzymes thatare beneficial to plants and do little to discourage its growth.Algae require two things to flourish: light and oxygen. If one or theother is not present, algae will not grow. In hydroponics, algaegrowth can be limited or excluded by ensuring that channels andpipes are light proof. For systems that use a growing substrate, blackplastic film can be cut to size and placed over the growing containerso that light cannot reach the medium however; it also blocks airexchange to the medium. To prevent algal growth in nutrientreservoirs, cover with a lid, plastic film or hessian bag to excludelight. Between plantings, all containers, channels or pipes, irrigationlines and the nutrient reservoir should be thoroughly flushed witha mild solution of chlorine or ordinary household bleach, then withfresh water.

Some very good home-made insecticidal recipes have beenhanded down over time. One such concoction is to dissolve a 2-cmcube of pure soap in a saucepan of hot water, add a crushed clove ofgarlic, and an onion or a few hot chillies, finely chopped or juiced,or cayenne pepper. Once blended add cold water to make 4 litres ofworking solution.

Another effective home-made concoction is tobacco juice,where the tobacco leaf is soaked in water for several hours to concocta filthy brown, repugnant liquid. Tobacco juice is particularlyeffective against spider mite.

Companion plantingCompanion planting means mixing plants in a row so that thosewith unpleasant odour, taste or other characteristic repel pests fromthe host plants that they like and damage. Generally, insects find themix of plants not to their liking and leave the garden for betterfeeding grounds. Finding which plants work best for interplantingis a matter of trial and error, but the list in the side column will behelpful for hydroponics plants.

Sticky trapsSticky traps are closely related to companion planting in that theyconfuse, lure or trap pests. Therefore, only special sticky trapsshould be used, ones that have been specifically designed for certaininsects. These traps use floral or plant scents or specific sexual scentsfrom specific insects to lure pests. Some traps are also made withcertain attractive colours, such as yellow which is renowned forattracting whiteflies.

When insect infestations occur, it is sometimes necessary toimplement a number of strategies in close succession. For homegardeners, an effective management plan to keep in mind is to:

• Identify pest insects and know their natural enemies• Monitor insect populations with sticky traps• Determine the level of plant injury• If the population is above acceptable levels, use one or more

control strategies• Evaluate the effect of the strategy

Algae controlAlgae are a common occurrence in hydroponic systems. It can beunsightly and, on drying, it can emit a foul odour. It will also robthe nutrient solution of minute elements, including oxygen. My own

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Plant repellent InsectMint, sage, rosemary Cabbage

worm Onion, garlic Spider miteRadish Stink bugMarigold Tomato

hornworm, thrips, whitefly

Geranium Leaf hopperSpearmint, tansy, Antspennyroyal

Traps and barriersAfter biological controls have failedto stem an insect strike, and beforeturning to sprays and dusts, considertrapping the enemy. One of the mostpopular traps is nothing more than ashallow dish or jar lid containingsome stale beer. Snails and slugswill drown in the stuff at night.Alternatively, a perimeter of woodash scattered around the base ofplants will block many crawling andwalking insects.

AlgaeAlgae may play a surprising role inthe growth of plants however; it isalso known to rob nutrient solutionsof precious oxygen and minerals.

Maximise growth

In recirculating hydroponic systems the growing plants feed onnutrients in the solution. When the nutrients are used by thegrowing plants this depletes the concentration of the overall solutionand changes the pH and EC. Left without adjustment plant growthwill slow, and plant health compromised. To maintain optimumgrowth, the nutrient solution needs to be either refreshed ordiscarded and replaced with a new solution.If plants remove acidic nutrients, the solution becomes morealkaline. In the same way, if plants use up alkaline salts the solutionwill become more acidic. As plants grow in size and pass throughdifferent stages of growth to maturity, they require differentnutrients and more and more nutrients to maintain their mass andgrowth. The concentration of the nutrient solution is adjusted byadding fresh nutrients and the pH and EC of the solution adjustedusing pH buffer solutions and fresh water.

It is easy to maximise the growth of plants by following thesethree steps each day:

• Top up the level of the nutrient reservoir with fresh water andcirculate for a short time to blend the water and nutrients.

• Test the nutrient concentration with an EC, TDS or cF meter.For most young leafy vegetables the strength should be around500-750 parts per million (ppm), and for mature vine plantsbetween 1000-2400 ppm, depending on variety. Generally, thelarger the tomato variety, the high the EC. Sweetness can alsobe encouraged with a higher EC, although the trade-off is asmaller fruit. Increase the nutrient concentration by adding alittle at a time of the make-up solution until the desired EC isachieved. In a recirculating unit, it may take some time for thesolution to blend throughout the system. If solution EC is toohigh, remove some of the solution and add fresh water until thecorrect EC is achieved.

• Test the pH of the solution. The pH should read around 5.5 to6.0 for most plants. If the pH is too low, add ‘pH raise’, a little ata time until the desired pH is reached. If the pH is too high, add‘pH lower’. Do not use concentrated pH raise or pH lower as itis too easy to overshoot the correct pH level.

As a general comment, buffer solutions should be used sparingly asthey add extra phosphorus (phosphoric acid), or nitrogen (nitricacid) or potassium (potassium hydroxide) to the nutrient mix and

The good running order of a hydroponic system depends ona good maintenance and management programme. Each dayabout 5 – 10 minutes should be set aside to inspect your

hydroponic system for any problems, such as system blockages,equipment fatigue or failure, insect infestations, or the early signs ofplant disease or plant malnutrition.

A common problem with an NFT system is a nutrient flowblockage. This can be caused by a blocked filter, algae growth inmicro-irrigation lines, or a root system growing into channel outlets.Depending on the size of the channel in use, and the type of plantbeing cultivated, plant roots may sometimes need to be trimmed toprevent ‘ponding’. This is where the nutrient solution forms poolsbetween plants owing to large root structures within the channel,thus preventing the normal flow of the nutrient film. Excessiveponding may cause root rot and plant death.

Systems that use sand as the growing substrate should bechecked daily to ensure that ‘puddling’ does not occur. A typicalexample of puddling can be seen on a beach by watching footstepimpressions on sand close to the water’s edge. Water quickly risesfrom below to form a puddle. In hydroponics, puddling causes plantroots to be constantly immersed in the nutrient solution, which willeventually cause plant death. To avoid puddling ensure thesubstrate drains well. Drainage can be improved by mixing coarsesand or gravel with fine sand.

At the end of the growing season, or between crops, the systemshoukd be thoroughly stripped and cleaned using a hard scrubber anda mild solution of chlorine (household bleach). Ensure that all theirrigation lines are also cleaned. After circulating the cleaning solutionthrough the system for up to two hours, empty the solution, drain thereservoir and flush the system again using fresh, clean water. Beforestarting the next crop, ensure the pump and filter are clean.

Care should also be taken with test equipment such as pHand EC metres. With proper care they will provide years of accuratetesting and control.

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Maintaining yoursystem

A mixed crop of Asian herbs and fancylettuce for the dining table.

Two tomato plants grown in a closed drip-irriation system and cocopeat substrate.

Mizuna grown in a vertical NFT system.The plants have been left to go to seed for

the following year’s planting.

of the problem. Any corrective action will filter through to the plantafter a further 7-10 days.

If you scale up your hydroponic activities to any significantdegree, you may benefit from making a financial analysis of yourenterprise. This should take into account capital costs, operatingcosts (e.g. fuel and electricity), equipment repairs and maintenance,and consumables (e.g. nutrients, buffer and calibration solutions).

If you keep a record of your hydroponic activities, it isuseful to write up all of the data into a summary after harvest.Remember, by keeping good records you will be able to quicklyfine-tune your growing skills and maximise the potential of yourhydroponic garden.

will alter the balance of the nutrient formulation. Most plants willgrow and thrive over a wide pH range and it is not necessary tomake frequent pH adjustments.

Calibrating meters

If you are using pH and EC ‘pen-type’ meters, they will requireperiodic calibration. Each meter has specific calibration solutionsthat can be purchased from retail hydroponic outlets, aquariumstores, and some garden nurseries. A calibration solution is alaboratory-grade solution guaranteed to conform to a set pH orconductivity.

For pH meters, the typical calibration solutions are pH 7.0and pH 4.0. The usual practice is to use the calibration solutionclosest to the pH of the nutrient formulation in use. For most plants,a calibration solution of pH 7.0 is best. For conductivity meters, atypical calibration solution is cF 2.76 mS/cm (equivalent to a readingof 1382 ppm for a TDS meter).

The process of calibration is simple. Clean your meter withfresh water to remove any grime and grit then dry it. A dirty or wetmeter will contaminate the calibration solution, rendering aninaccurate reading. Immerse the probe into the calibration solutionfor around 1 minute to allow any temperature compensation featureto adjust then check the reading. If the meter is correctly calibrated,the reading should be the same as the calibration solution. Forexample, for a pH 7.0 calibration solution, the meter should read pH7.0. If this is not the case, some meters will allow you to adjust themeter automatically using a push-button feature, while othersrequire manual adjustment using a jeweller’s screwdriver.Conductivity meters are calibrated in the same manner.

Keeping records

Good records are invaluable to the serious hydroponic homegardener, enabling comparisons from crop to crop and from seasonto season. Any unusual observations should be recorded, such asinsect strikes which affect some plants but not others. You may liketo develop your own companion planting guide to prevent suchstrikes occurring in future crops.

In most cases, if a problem develops it can usually be tracedback to a specific point in time. From my experience, it usually takes7-10 days for most plants to show visible symptoms of a malady.Once again, a record of your activities may help to isolate the cause

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Submerged metersMost electronic meters are notwaterproof. In the case of pocketmeters, they are designed to beimmersed only to around one-third oftheir depth. If the worst happens andyou drop your meter into the nutrientsolution, don’t panic. If you actpromptly, there need be little or nodamage to it.On recovering your meter, open the

top and take out the small batterymodule. Remove and dry thebatteries. Turn the meter upsidedown to drain any water. Pour in ateaspoon of methylated spirits, shakeand drain. Do this again. As soon aspossible, take the meter to a servicestation and blow out any remainingwater with compressed air.Once it is dry, spray a lubricant,

such as WD-40 or equivalent, on asoft cloth, wipe the batteries andreplace them, making sure that theyare inserted the right way. If you haveacted promptly, your meter shouldhave suffered little or no damage, andwill now be back in working order.

nutrients as they do in soil, and the environment can be manipulatedto some extent.

Generally, hydroponically grown fruit and vegetables are larger insize and, if grown to optimum conditions, the quality of the produceis much higher. Once again, this is because plants receive a well-balanced diet of water and nutrients.

Most plants can be grown hydroponically, although some plantsgrow better in some systems than in others. For example, lettuce andherbs are well-suited to water culture, and vine crops grow betterin substrate systems. The only exception is fungi, such asmushrooms, whose nutrient requirement is completely differentfrom that of plants and cannot be grown hydroponically.

No. Hydroponically grown plants use the same inorganic elementsas those that are found in soil. When compost and manures areadded to soil, it takes time decompose into the inorganic elementsnecessary for plant growth. In hydroponics, the same inorganicelements are supplied to plants directly.

The uptake of water and nutrients depends on the demands ofphotosynthesis and transpiration by plants, and these factorsdepend on the leaf area of the plant, light intensity, light duration,air temperature, relative humidity and wind factor, among otherenvironmental factors. For example, a plant with five times moreleaf area than a younger plant of the same variety will take upapproximately five times more water and nutrient under similarconditions. The same plant will have a higher uptake in hot, dryconditions than in cool, humid conditions. Also, plants grownindoors, under heavy shade or during cloudy weather will demandfar less water and nutrients than if the same plants were grown indirect sunlight.

All growing mediums can be re-used, unless there has been a rootdisease in the system. In this case the medium needs to be sterilisedor replaced altogether. Some mediums such as rockwool and cocopeat perform better with successive crops.

Wherever there is light and oxygen, algae will grow. However, in amedium system this is rarely a problem as long as the system isperforming effectively. More care needs to be taken in systems thatuse no medium. Plant roots do not like light. If algae is growing in

Hydroponics, also known as soilless culture, is the science ofgrowing plants without soil. Nutrients and water are deliveredstraight to the roots of the plant, allowing plants to grow faster andharvesting to occur sooner. Hydroponics is capable of deliveringconsistent high quality produce from plants that out yieldconventional production systems. In a scientific sense, hydroponicshas been around for over three centuries, but only in recent decadeshas it become an important food production system. Today,hydroponic products are distributed through all the normalwholesale and retail distribution channels. Here we answer the tenmost commonly asked questions about hydroponics.

Hydroponically grown fruit and vegetables have the samenutritional values as those grown in soil, provided they areconsumed soon after harvesting. The longer any produce is leftbefore consumption, the lower its nutritional value. Therefore,produce that is grown for supermarkets, whether hydroponics or insoil, will progressively lose nutritional value as it is finding its wayto the supermarket shelf and then to the consumer’s table. Tominimise loss of nutrition, some hydroponically grown plants areharvested and conveyed to the supermarket with the roots stillattached, so that they remain fresh until purchased by the consumer.

Hydroponic fruit and vegetables taste as good as those grown in soil,provided they are grown to optimum levels. However, produce willlack flavour if cultivated outside what are considered to be theoptimum growing conditions for that plant. For example, if theconductivity for a tomato plant is not kept within acceptable limits,produce will be soft and lack flavour.

Not all plants grow faster in hydroponics. Generally, plants such asferns and Australian natives share the same growing profile,regardless of whether they are grown in soil or hydroponics,although the latter have larger leaves and a better overallappearance. This is because they receive the full spectrum ofnutrients. Hydroponically grown flowers, vegetables and fruits dogrow faster – about a third faster – than those grown in soil,provided they are grown to their optimum growing conditions. Thisis because plants do not have to search or compete for available

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Common questions abouthydroponics

How nutritious arehydroponically grown vegetablesand fruits?

Do hydroponically grown fruitand vegetables taste better thansoil-grown produce?

Is it true that hydroponic plantsmature faster than soil-grownplants?

Is it true that hydroponic fruit andvegetables are larger than soil-grown produce?

Can all plants be grownin hydroponics?

Are inorganic nutrients harmful in hydroponics?

How much nutrient solution do plants take up daily?

Can the growing medium be re-used?

Is algae harmful to plants?

Barry, Carl, Nutrient Handbook, Rev. Ed., Casper Publications, Sydney, 2010

Colcheedas, Tom, Hydroponics Simplified, Melbourne, 1992

Cooper, Dr Allan, The ABC of NFT, Casper Publications, Sydney, 2008

Douglas, James Sholto, Advanced Guide to Hydroponics, Penguin, London, 1976

Garzoli, Dr Keith, Greener Greenhouses, Casper Publications, Sydney, 2003

Mason, John, Commercial Hydroponics, Kangaroo Press, Sydney, 1990

Patten, George van, Hydroponic Basics, Van Patten Publishing, 2004

Practical Hydroponics & Greenhousesmagazine, Casper Publications, Sydney, 1991-2015

Resh, Howard M., Hydroponic Food Production, Rev. Ed., Woodbride Press, Santa Barbara, 2012

Resh, Howard M., Hydroponic Home Food Gardens, Rev. Ed., Woodbridge Press, Santa Barbara, 2003

Ross, Jack, Hydroponic Tomato Production, Casper Publications, Sydney, 2007

Smith, Denis l., Rockwool in Horticulture, Grower Books, London, 1987

Sundstrom, A.C., Simple Hydroponics, Penguin, Melbourne 1979

Sutherland, Dr Struan K. & Sutheland, Jennifer, Hydroponics for Everyone, Rev. Ed, Hyland House, Melb, 1999.

the channel, then it is an indication that too much light is enteringthe system and steps need to be taken to eliminate it.

The cost of a hydroponic system depends on the degree of itsautomation. For most home gardeners, simple hydroponic systemscan be constructed using unused materials usually found in mostbackyards and sheds. Equipment such as pumps and timers can beadapted to most systems simply and inexpensively. Nutrients arean ongoing cost, but these are inexpensive to purchase and go a longway, depending on the size of the hydroponic enterprise.

No. Hydroponic techniques are now recognised as a practicable andachievable solution to the world’s growing food shortages,especially in Third World countries exposed to populationpressures, and in countries that lack good arable land and scarcewater resources. Compared to traditional soil farming, cropturnaround is accelerated and pest and disease problems arereduced somewhat. From an environmental perspective,hydroponics contributes to water conservation.

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Is hydroponics expensive toestablish and run?

Is hydroponics just a trend?

Further reading

After your first harvest yon will delight inhow simple hydroponic gardening is, andhow nutritious, flavoursome and fragranthydroponically grown vegetables, fruit andflowers can be!

Hydroponics for the home gardener is an economical and simpleway to turn your backyard, no matter how big or small, or balconyinto productive vegetable, herb and flower gardens.

Hydroponic Gardening, designed for beginners of all ages, teachesthe basics of hydroponic gardening—how to grow hydroponicplants from seed, and to feed them with naturally balancednutrients. It also shows you how to transplant plants from soil tohydroponics and how to take clones from valuable plant stock forhydroponic cultivation.

Once your hydroponic garden is established, learn all about:

• the fundamental principles of nutrient management and nutrition•how to recognise and remedy nutritional disorders•how to combat pests and diseases the natural way•how to maintain an ecological balance in your hydroponic garden.

Steven Carruthers is the founder and publisher of Practical Hydroponics & Greenhouses magazine.