greenhouse hobby

8/9/2019 Greenhouse Hobby

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additional heater because green-houses lose heat five to tentimes faster than an equivalentarea of home. The cost of heat-ing an attached greenhouse may

be less than that of heating afreestanding greenhouse of thesame floor area because onewall is not exposed; however, at-tached greenhouses usually re-ceive less light for the same rea-son. Straight-side lean-to, slant-side lean-to, and curved-sidelean-to styles are ideally suitedfor small, easy-to-construct at-tached greenhouses (Figures 2a-c), although the Quonset, gothicarch, slant-side, and gable roof

(Figure 2d) freestanding stylescan also be attached. A solidfoundation similar to the housefoundation is often required orhighly desirable for attachedgreenhouses. Joining and sealingthe greenhouse to the houseneeds special attention. Consultan architect or building contrac-tor to determine the method ofattachment.

Step 3: Choo se alocation for yourgreenhouse.

Often, there may be a limit-

ed choice of locations that willhave adeq uate sunlight, ade-quate soil drainage, easy accessfor people and materials, access

to utilities, and a pleasing blendwith the landscape. For manyhomeowners, the appearance ofthe structure is most important,so compromises must be madeto meet other location require-ments.

One of the most important

location requirements is sun ex-posure. Many flowering pottedplants require full sun to per-form well. A freestanding green-house for these p lants should beconstructed with the long sidesof the building facing southeastto southwest (Figure 3). Vege-table and flower seedlings fortransplanting outdoors in thespring need maximum sunlight,so choose a location that re-ceives full sun. For plants requir-

ing less light, the greenhousecan face northeast to southeastor northwest to southwest.Exposure is particularly impor-tant for attached greenhouses.Consider these locations inorder: firstsouth or southeast,secondeast, thirdsouthwest,fourthwest, and lastnorth.Keep in mind that a western ex-posure can be too hot in sum-mer, and a northern exposureusually does not receive enoughlight for most plants. Also beaware that tall structures andtrees near the greenhouse mayblock light for parts of the day.

Figure 2. Attached hobby greenhouse styles

(a) straight-side lean-to

(c) slant-side lean-to

(b) curved-side lean-to

(d) attached gable

Figure 3. Location priori-ties for a hobby greenhousebased on ambient sunlight

W

E

NS

Winter NoonWinterSunset

Winter Sunrise

Summer Noon

SummerSunset

Summer Sunrise

Best location

Good location

Poor location

Hobby Greenhouse Construction 3


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4 Alabama Cooperative Extension System

Falling limbs can also be a majorproblem if the greenhouse is lo-cated too close to trees.

Other location considerationsinclude ensuring that the site islevel and that the soil drainswell. Many locations may haveto be graded to ensure that the

foundation is level. Slope thesoil away from the greenhouseto drain rainwater away. Ifdrainage is a problem, considerinstalling drainage tile beforeconstructing the greenhouse.

Avoid low areas with poorair drainage, especially thosesurrounded by woods or build-ings. Cold, humid air can stag-nate in these locations and in-crease heating costs. Conversely,avoid high elevations with directexposure to strong winter winds.Convective heat loss through thecovering material can increaseheating demand.

The greenhouse should beconvenient to a driveway to re-ceive supplies and to haul awayplants or garbage when needed.Walkways to and from the gar-den, house, and storage areasand access to water, fuel forheating, and electricity should all

be considered.The greenhouse should con-

tribute to the app earance of thehome and landscape and not bean eyesore either to the owneror neighbors. Consider room forexpansion if you think you maybe so inclined in the future.

Step 4: Choo se a

greenho use size

to suit your nee ds.

Available space and costusually have a large impact onthe choice of size for a hobbygreenhouse. Keep in mind, how-ever, that a greenhouse that istoo small may cost more to op-erate than the initial cost ofbuilding a larger one. The obvi-ous problem with a small green-

house is that it is too small tomeet the needs of the owner. Inaddition, temperatures can fluc-tuate rapidly in a small green-house, and heat losses can be ashigh as they are in a largergreenhouse. Small houses mayalso have limited headroom and

be hard to work in. A taller, larg-er greenhouse obviously hasmore space, and it heats andcools more uniformly than ashorter, smaller one.

As a starting point, 100square feet would be a mini-mum size, but 200 square feet isbetter. A house 9 to 14 feet wideby 20 feet long can be managedin a few hours per week. A larg-er greenhouse can also cost lessto cover per square foot than a

small greenhouse, so choo se asize slightly larger than youthink you need. On the otherhand, ask yourself, do you havethe time and dedication to main-tain a large greenhouse, nowand in the future?

Step 5: Choo se acovering m aterial.

There are several coveringmaterials to choose from, each

of which has its own advantagesand disadvantages. Commoncovering materials are glass,polyethylene film, fiberglass re-inforced panels, and double-layer structured panels.

Glass

Glass is the traditional green-house covering against which allothers are judged. Good-qualityglass is an attractive, very trans-

parent, and formal (in ap pear-ance) covering material. It isvery strong (tensile strength), butit is subject to shattering and canbecome brittle with age. Glass isalso very expensive and becauseof its weight requires sturdierframing support than is requiredwith other covering materials.Originally, glass pan es for green-

houses were 18 by 16 inches,but larger sizes are more com-mon now. Actually, larger panesare less fragile than smallerpanes. Many greenhouses arecovered with double-strengthfloat glass (1/8 inch thick) cost-ing $0.85 to $2.00 per square

foot. Large glass panes in manymore expensive greenhouse kitsare tempered glass (5/32 inchthick) costing $3.00 to $7.00 persquare foot, depending on thepane size.

Polyethylene Film

Polyethylene film (PE) is agood choice for home-builtgreenhouses because less struc-tural support is required and itcosts much less than other mate-rials. However, PE film only lastsabout 2 years. Clear PE is usedfor growing most plants, butwhite PE can be used to reducelight and heat for growing low-light plants or for propagation.PE manufactured for greenhouseapplication comes in widthsfrom 10 to 50 feet, thicknessesfrom 1 to 8 millimeters, andcosts $0.06 to $0.09 per squarefoot. Two layers of PE are fre-

quently applied to greenhousesto reduce heating demand.Double-layer PE houses general-ly cost 30 to 40 percent less toheat than single-layered housesdo. The two layers are kept air-inflated by a 100- to 150-cubic-foot-per-minute squirrel cageblower mounted to the inside PElayer. Purchase 4-millimeter PEfor the inside and 4- or 6-mil-limeter PE for the outside. Use 6-millimeter PE for single-layer ap-

plications. PE can be installed onwood-frame greenhouses bynailing wood batten strips overthe film into the foundationboards and rafters or arches.However, because PE must bereplaced frequently, investing inspecial fasteners makes the jobeasier. Fastening systems areavailable for single- or double-layer applications.


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Fiberglass Reinfor ced

Panels

Fiberglass reinforced pan els(FRPs) are rigid plastic panelsmade from acrylic or polycar-bonate that come in large corru-gated or flat sheets. FRPs areavailable in 24- to 57-inch widths

and up to 24-foot lengths. FRPsare durable, retain heat betterthan glass does, and are light-weight (less structural supportneeded). Large panels are flexi-ble enough to be applied to aQuonset greenhouse. Light trans-mission may be better than glasssimply because less structuralsupport is needed, which createsless shadow. The prices of FRPsrange from $1.00 to $1.25 persquare foot, depending on theguaranteed life span of the mate-rial. Inexpensive materials maybe guaranteed for as little as 5years; more expensive types maybe guaranteed for as long as 20years.

Double-Layer Structured

Panels

Acrylic or polycarbonatedouble-layer structured panels(DSPs) are made of two layers ofplastic held apart by ribs spaced12 to 1 inch apart. The double-layer construction increasesstructural strength and heat re-tention but decreases light trans-mission compared to single-layermaterials. Panels are 4 feet wideand up to 39 feet long. DSPsmade of polycarbonate cost$1.75 to $2.50 per square foot,and those made of acrylic cost$2.00 to $3.50 per square foot.

Step 6: Choo se theframin g m aterials.

To a large extent, this choicewill be influenced by the type ofcovering material chosen, thedesired permanence, and costs.Many homemade greenhousesare made of wood. Be sure topurchase treated lumber for ex-terior use. Metal-framed green-houses are more permanent butare difficult for do-it-yourselfprojects from scratch. However,greenhouse manufacturers offermany kits that are easy to erectand are reasonably priced.Aluminum or galvanized framinglast a long time with little main-tenance. Schedule 80 PVC pipecan also be used as supports for

small Quonset-style greenhousesthat are to be covered in PE, butPVC requires extra support towithstand strong wind.

Whatever the choice, theframing must adequately supportthe covering and any equipmentand/or hanging baskets suspend-ed from the framing. The fram-ing must also be able to with-stand wind, rain, snow, or icecommon to the geographic loca-tion. The load exerted by hang-

ing baskets can be greater thanthat caused by weather.

Wood preservatives for green-house framing and benchesshould be pressure-treated, salt-type, or copper naphthenate.Avoid creosote (no longer legal)and pentachlorophenol preserva-tivesthese are dangerous forpeople and toxic to plants.

The eave height for a gableroof greenhouse should be at

least 51

2 feet with a minimumgable height of 8 feet. However,gable heights of 10 to 15 feet arecommon. Roof pitch for a glassgreenhouse should be 6-inchrise per foot (27 degrees) to pre-vent inside condensation fromdripping on plants. Plastic-cov-ered greenhouses require asteeper pitch of 7- to 812-footrise per foot to prevent drip.

Step 7: Choo se thefoundation and side-wall materials.

Greenhouses to be coveredin PE usually do not require anextensive foundation, but thesupport posts must be set in

concrete footings. The problemwith a PE-covered Quonsethouse is usually not holding itup but holding it down. Instrong wind, the shape of thehouse makes it function like anairplane wing, and it may lift offthe ground. Figure 4 shows asimple poured concrete footingand a concrete block foundation.

Figure 4. Simple concrete founda-tions for a hobby greenhouse

Poured

Concrete

Concrete

Block

6 minimum

Below

Frost

Line

12 16

512 712

Attached greenhouses andthose covered with glass shouldhave a strong concrete or con-crete block foundation that ex-tends below the frost line ac-cording to local building codes.A 2- to 3-foot-high sidewall canadd considerably to the appear-ance o f a greenhouse. Concreteblock, stone, or brick are themost popular materials used, butshingle, clapboard, and asbestosrock have also been used.Choose the type that works bestwith the overall architecturalscheme.


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Step 8: Choo se the typeof fl oor and walkways.

In many places wheredrainage is adequate, a solidfloor is not necessary. Four inch-es of34-inch crushed stone orpea gravel will help controlweeds and provide a porousmedium for water to evaporatein the summer to provide somecooling. If you want a solid con-crete floor, install one or moreFrench drains, and slope thefloor toward the drains. Dontforget to plan for plumbingwhen planning the foundation.

Walkways can be constructedof concrete for easy movement ofequipment and people, especiallyif a family member is disabled or

in a wheelchair. Brick filled withsand, flagstone, or stepping stonescan be used for decorative walks.Gravel under the benches keepsthe walkways free of debris andreduces weeds. Walkways can be2 to 3 feet wide in a small green-house. Adjust the width of walksif a cart or wheelbarrow will beused. Larger greenhouses oftenhave 2- to 3-foot secondary aislesand a 4- to 6-foot main aisle. If afamily member is in a wheelchair,

use at least 4-foot-wide aisles andramps for easy access.

Step 9: Choose the typeof benches to install.

Benches can be constructedfrom a variety of materials andarranged in many different ways.If you plan carefully, 70 to 80 per-cent of the floor area can be de-voted to growing plants. Makesure that the supports for benches

are strong enough to hold thelargest number of plants and thelargest container size anticipated.Wood, metal pipe, or concreteblock can be used as bench sup-ports.

Also make sure the benchsurface is strong enough to sup-port plants without sagging butthat it is open to allow water

drainage and air movement.Spruce or redwood lath and 14-gauge welded wire fabric or ex-panded metal make a strong,long-lasting, open bench top.Benches should be 2 to 3 feetwide with access from one sideor 4 to 5 feet wide with access

from both sides. If using solid-topped benches, set them backfrom the sidewall of the green-house by 6 inches to allow airmovement. No setback is need-ed for open-top benches.Benches should be 24 to 36inches high; for individuals inwheelchairs, bench heightshould be 30 to 36 inches, withlittle or no surface lip. Placebench supports 6 to 12 inchesback from the surface edge to

provide knee room.

Step 10: Decide h owto he at yourgreenhouse.

Greenhouses are poorly in-sulated structures, and heat lossthrough the covering on cold,clear, windy nights can be con-siderable. Heat can be suppliedusing electricity (can be expen-sive), natural gas or propane,fuel oil, solar energy (unreli-able), or kerosene (emergencyuse only). You can also connectthe greenhouse to your homeheating system. Natural gas orpropane are probably the mostcost-effective ways of heating ahobby greenhouse. If natural gasis available in the home, plumb-ing into the existing line savesconsiderable cost over a newmeter and gas line. If natural gas

is not available, check with thelocal propane gas company forcost and availability. Determineif the company provides a stor-age tank free or if it can be rent-ed or purchased. Consult thecompany to determine the tanksize appropriate for the green-house.

A variety of gas unit heatersare available to heat hobby

greenhouses. Some are designedto hang from the structure of thegreenhouse; others sit on thefloor. Costs for gas unit heatersrange from $300 to $550 for20,000 to 60,000 BTU units, re-spectively. Unit heaters burn gasin a firebox. Heated air rises

through the inside of a thin-walled heat exchanger on theway to the exhaust chimney. Afan draws air in from the green-house, across the outside of theheat exchanger, and out into thegreenhouse. Thus, most of theheat is removed from the ex-haust before it exits the struc-ture. The exhaust chimney mustbe sufficiently tall to maintain anupward draft and extend abovethe greenhouse roof. An 8- to

12-foot chimney is usually suffi-cient. All open-flame heatersmust be vented to the outsideand given a fresh air supply forcomplete combustion. Fresh airshould be provided by an unob-structed opening to avoid carbondioxide buildup .

In larger greenhouses, aplastic tube system may beneeded to distribute the heatevenly within the house. Thesystem consists of a perforatedpolyethylene tube suspendedoverhead in the ridge and ex-tending the length of the green-house. A fan connected to thetube blows warm air from theheater into the tube for green-house distribution. This systemcan also be used for circulatinginternal air when heating orcooling are not required.

A variety of electric resis-tance heaters can also be used.

Costs range from $100 to $350for 5,000 to 17,000 BTU units,respectively. Those available indepartment stores and homecenters are usually only ade-quate in the smallest greenhousefor starting seedlings in thespring. Larger units can be pur-chased, but op erating them canbe costly.


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Heater size for a givengreenhouse and geographic lo-cation depends on the surfacearea of the greenhouse and thetemperature difference betweenthe inside and outside of thegreenhouse. To determine thesize heating system you need,

calculate the total surface area ofthe greenhouse covering. Thendetermine the d ifference be-tween the minimum expectedoutside temperature during win-ter in your area (see the USDAhardiness zone map, average an-nual minimum temperature) andthe maximum night temperatureyou wish to maintain (generally60 to 65 degrees F). Multiply thegreenhouse surface area by thetemperature difference by the

heat loss conversion factor inTable 1 for the appropriate cov-ering. The answer will be inBTUs per hour. Most heaters arerated in this unit. Many green-house supply or constructioncompanies can help you deter-mine the p roper size heater foryour situation.

Step 11: Decide h owto ventilate your

greenhouse.The purposes of ventilation

are to exchange carbon dioxideand oxygen, to remove hot air,and to lower relative humidity.Hobby greenhouses can be vent-ed by natural flow-through ven-tilation or by forced-air ventila-tion. Flow-through ventilationrelies on side and top vents thatpull cool outside air into thegreenhouse through the side

vent as warm air rises and exitsthrough the top vent. The com-bined side and top vent area

should equal about 20 percentof the roof area. Vents can bemanually controlled, but this re-quires frequent temperaturechecks and vent adjustment ac-cording to outside conditions.Using an electric motor and ther-mostat for automatic vent control

is much easier. Simple automaticsystems open or close the ventsbased on a setpoint temperature.More advanced systems openand close vents in stages basedon multiple setpoint tempera-tures. The advantage of naturalflow-through ventilation is that itcosts less than forced-air ventila-tion to operate; however, it maynot be adequate to cool thegreenhouse during the summer.

Forced-air ventilation sys-

tems consist of a louvered intakevent and electric fan(s) con-trolled by a thermostat. The fanspull cool air into the greenhousefrom outside through an intakevent and p ush warm inside airout. Fans should be mounted ina waterproof housing with air-activated louvers to protect elec-trical components from in-clement weather and to keepcold air out during the winter.Be sure to install a screen overthe inside of the fans to preventinjury. Be sure that the distancebetween the fans and adjacentstructures equals at least 112times the fan diameter. The lou-ver on the intake vent on thewall opposite the fans can beair-activated or motorized. Costsof fans range from $150 to $250for 1,200- to 3,000-cubic-feet-per-minute units, respectively.

Be sure that the fan capacity

is large enough to exchange theair in the greenhouse at leastonce per minute. Recommen-

dations for warm climates callfor a fan capacity to remove 12to 17 cubic feet per minute persquare foot of floor area. If thegreenhouse is attached to theeast, west, or south wall of an-other building, solar heat willcollect inside the greenhouse

from this wall. If this is the case,add half the area of the attach-ment wall to the floor area whencalculating the ventilation re-quirements. Work with a green-house supply or constructioncompany to determine the prop-er size fan or vent for your situa-tion.

Step 12: Decide h ow tocool your greenho use.

One of the best ways to coola greenhouse in the summer isto reduce light intensity. Howmuch reduction to provide de-pends on the heat load in thegreenhouse and the light re-quirements of the plants grown.Greenhouse whitewash, shadecloth, screens of wood or alu-minum, or Vene tian blinds canbe used for shading. Green-house whitewash is a specialkind of latex paint that is diluted

in water and sprayed on thecovering surface. It is designedto be applied in the spring andgradually degrade by the actionof rain and sun so that little re-mains by fall. Shade cloth is ablack, green, or white wovenfabric of polypropylene that islaid over the outside of the cov-ering. Shade cloth can be pur-chased with various weave den-sities that result in 20 to 80percent light reduction. For mosthobby greenhouse app lications,30 to 50 percent light reductionshould be sufficient.

Another method for coolinga greenhouse is evaporativecooling, which relies on air pass-ing through a porous pad satu-rated with water. The evaporat-ing water removes heat from the

Table 1. Heat Loss Factor for a Small Hobby Greenhouse

Greenhouse covering Heat loss (calm area) Heat loss (windy area)

Polyethylene or fiberglass 1.2* 1.4Glass 1.5 1.8Double-layer plastic 0.8 1.0

*Heat loss in BTU/h our/ square feet/F


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greenhouse. There are two typesof evaporative coolers: fan-and-pad systems and unit coolers(swamp coolers). Fan-and-padsystems consist of a cellulosepad at least 2 feet tall and ex-tending the length of one wall,with water supplied from the top

to keep the pad wet during op-eration. Fans are installed in theopposite wall to draw outside airthrough the pads.

Unit coolers consist of ametal box mounted outside thegreenhouse and evaporativepads on three inside walls.These units may be more practi-cal and attractive for smallhobby greenhouses. A waterconnection, collection lines, andrecirculating pump are built into

the unit. A fan within the unitdraws outside air through thepads and the cooled air into thegreenhouse through a duct. Avent on the opposite side of thegreenhouse provides an air exit.Unit coolers should provideabout 15 cubic feet per minutefor each square foot of floorarea. Costs for unit coolers rangefrom $125 to $600 for 500- to3,500-cubic-feet-per-minuteunits, respectively. Determiningthe evaporative cooling capacityfor a given greenhouse and geo-graphic location is difficult. Workwith a greenhouse supply orconstruction company to deter-mine the proper size for your sit-uation.

Generally, heating, ventilat-ing, and cooling are controlledby thermostats located close tothe center of the greenhouse atplant level. For accurate control,

be sure the thermostat is shadedfrom direct sunlight. Mounting itin a plastic or wood box venti-lated by a small blower workswell.

Step 13: Decide h ow toprovide utilities to yourgreenhouse.

Check all local buildingcodes before building a green-house on your property. Somecounty or city codes prohibit

greenhouses or place restrictionson size, type, covering, or con-struction materials. Also, checkwith the local electric company.In some areas, the utility compa-ny may request a utility pole andseparate meter for the green-house. Be sure all electricalwork is performed by a licensedelectrician according to code.

Water can usually beplumbed from the home supplyline as long as the volume and

pressure are adequate. Install abackflow prevention valve in thewater supply line to prevent thepossibility of contaminating thewater in your home.

Step 14: Choo se w orkand s torage areas.

Make a work area for pottingand maintaining plants. This maybe located inside or outside thegreenhouse. The north wall is

often a good location for a workarea inside the greenho use. Thework area may also include asink. Storage areas for soil andcontainers can be located out-side the greenhouse but shouldbe protected from the weatherand not be an eyesore.

Step 15: Follow thegreenh ouse dos

and donts.Finally, consider the follow-

ing points. They are intended toprevent problems and to makelife with a greenhouse more en-joyable.

Dos:

Keep the greenhouse and sur-rounding areas clean and orga-nized.

Allot enough time to thegreenhouse weekly to be suc-cessful.

Learn more about greenhousesand growing plants by readingand talking to others.

Keep the greenhouse in agood state of repair.

Discard weak, diseased, orbadly insect-infected plants.

Enjoy the greenhouse; arrangework intelligently so it doesntbecome a chore.

Experimenttry somethingnew!

Donts:

Dont take in every friendssick plant. Youre asking fortrouble if you do!

Dont start with the most diffi-cult plants. Gain experience withplants that are easier to grow be-fore trying the difficult ones.

Plants in a greenhouse are aresponsibility. Dont leave them

without care.


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ANR-1105

J.R. Kessler, Jr.,Extension Horticulturist, Assistant Professor, Horticulture,Auburn University

For m ore information, call your county Extension office. Look in your tele-phone directory under your countys name to find the number.

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The AlabamaCooperative Extension System (Alabama A&M University and Auburn University) offers educational programs,materials, and equal o pportunity employment to all peop le without regard to race, color, national origin, religion,sex, age, veteran status, or disability. UPS, 6M30, New May 199 8, ANR-1105
http://www.aces.edu/

greenhouse hobby

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