horticulture science lesson 41 growing crops by hydroponics

Horticulture Science Lesson 41

Growing Crops by Hydroponics

Horticulture Science Lesson 41

Growing Crops by Hydroponics

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Interest ApproachInterest ApproachBring produce grown hydroponically to the class. Ask the students if there is anything special about the food. Ask them why the food would be produced hydroponically and not grown outdoors.


Student Learning ObjectivesStudent Learning Objectives•Prepare an overview of the production of hydroponically grown foods.

•Describe the production of lettuce and spinach by hydroponics.


Student Learning ObjectivesStudent Learning Objectives•Examine the hydroponic production of tomatoes.

•Discuss the application of hydroponics in cucumber production.


TermsTerms• bag culture• early fruiting stage• germination area• germination stage• mature fruiting stage• priming• seedling stage• vegetative stage


What is involved in the production of hydroponically grown foods?

• It is important to first establish an understanding about why hydroponic production is important.

• One reason is hydroponic production produces high-quality products. – Those products can be sold

locally, even in small amounts.



• Growers can control the environmental conditions in greenhouses to encourage optimum growth.

• Hydroponic operations require little land.

• Produce can also be grown in places that don’t support vegetable growth, such as deserts, and during unseasonable times, such as the winter months.



• The majority of commercial hydroponic operations produce vegetables and herbs.

• Top crops are lettuce, spinach, tomatoes, cucumbers, green peppers, melons, snap beans, squash, and eggplant. – Basil is the most widely grown

herb.– Strawberries are also grown in

hydroponic operations.



• The type of crop to be grown must be compatible with the hydroponic system.1. Nutrient film technique (NFT) is generally used for the production of lettuce, spinach, and other leafy vegetables. – These crops are also grown using aeroponic

systems.



2. An aggregate hydroponic system involves a solid, inert medium that provides support for the plants. – The support provided by the aggregate system

makes it the system of choice for growing heavier plants, including tomatoes, peppers, squash, cucumbers, and eggplant.

– The two most popular substrates are rock wool and perlite.



3. A type of aggregate culture used with cucumbers is bag culture. – Bag culture consists of polyethylene bags with

perlite or bark, composted bark, and rice hull mixtures.

– The bags are pre-punched or slit to provide drainage.

– Nutrient solution is delivered to the bags via micro-irrigation.



• Tomatoes, peppers, squash, cucumbers, and eggplant usually need additional support. – String, wire, cages, and other methods are

employed to keep the plants upright.

• Another important factor is pollination of the flowers. – Tomatoes, peppers, squash, eggplant, and

strawberries must be pollinated to produce fruit. Electric “bees,” or vibrating rods, can be used for small operations.

– For large operations (e.g., 10,000 square feet under one roof), bumblebees are used.



• To be successful in the hydroponic business, it is necessary to produce a large enough volume for the consumer. – The produce must be uniform and of high quality. – The scheduling must provide a dependable

supply of produce. – Also, the pricing must be competitive. – Production costs are generally higher for

hydroponically grown produce than for field-grown produce.


How are lettuce and spinach grown by hydroponics?

• Crops that grow very well in hydroponic systems are leafy vegetables.

• Heads of lettuce are usually grown in NFT pipe or deep trough (raft) systems.– Whole heads are harvested. Boston, Bibb or leaf

lettuce types are most frequently grown.



1. There are advantages associated with whole head lettuce production. – Lettuce grows rapidly, maturing in 50 to 60 days. – Lettuce grown in hydroponic systems is cleaner

than field-grown lettuce. – There is no dirt or grit. – Whole head lettuce doesn’t take up much space. – Also, since it is a cool-season crop, the grower

spends less on heating the greenhouse.

2. A disadvantage to head lettuce is that it must be marketed wholesale. – Summer production is difficult. – Diseases may appear in recirculating systems.



• Lettuce for salad mixes and edible flowers are usually sold as individual leaves trimmed off plants. – A typical salad mix consists of 2/3 red leaf

lettuce and 1/3 green oakleaf lettuce. – A chef mix might contain arugula, spinach,

chervil, endive, chicory, cress, and red mustard.

red leaf lettuce

green oakleaf lettuce



1. There are some advantages associated with salad lettuce. – Salad lettuce is a crop that can be grown in a

float system or NFT system. – It is easily marketed locally to chefs,

restaurants, specialty grocery stores, or farmers’ markets.

– The crop also displays rapid growth.

2. A disadvantage is that different types grow at different rates. – Therefore, they must be grown separately and

mixed later. – Salad lettuce is very perishable once cut, and it

requires intensive management.



• One example of a salad lettuce production schedule involves a germination area and a hydroponic area.1. Seeds are started in a germination area where they germinate and grow for 11 days. – The germination area is a location where the

environment is controlled to obtain the maximum rate of germination.



a. Plug trays are filled with germination medium.

• The medium is moistened.– An alternative is to use 1-inch-square rock wool plugs. – One lettuce seed is sown in each plug, and the trays are

misted to totally saturate the medium.


• De-ionized water made by a reverse osmosis (RO) process is recommended.

• RO water eliminates problems with chlorine or nutrients in the water that might affect fertility levels.

• The trays are placed on ebb-and-flood benches for subirrigation.

• They are given low light for 24 hours and 68°F (20°C) temperatures.

• The seed trays are covered with plastic to ensure a high humidity, which prevents the seeds from drying.


b. After 24 hours, equal parts of HydroSol and calcium nitrate (CaNO3) are added to RO water as a fertilizer solution. – The temperature is raised to 77°F (25°C). – Water pH is adjusted to 5.8. – Subirrigation continues for 15 minutes every 12

hours until Day 6. – Lighting remains at 24 hours, but the intensity is

increased.

c. On Day 2, the plastic covers are removed.


d. Seedlings are selected on Day 6 based on the size and expansion of a seedling’s first true leaf. – Seedlings that display poor growth are discarded.– Twenty to 30 percent of the seedlings may be

discarded. – Seedling selection is an important step for the

uniformity of the crop.

e. Also on Day 6, watering is increased to 15 minutes every 6 hours.f. On Day 11, leaves begin to overlap and roots appear through the bottom of the plugs.


2. The young plants are transported to the greenhouse and transplanted into the hydroponic system, where they are grown until harvest on Day 35.a. The seedling plugs are inserted into precut, square, centered holes in Styrofoam rafts or floats.b. Environmental conditions are kept the same until Day 35. – Day temperatures are maintained at 75°F (24°C),

and night temperatures at 65°F (18°C).


• A production schedule for spinach involves starting seeds in a germination area.

• The seedlings remain in the germination area for eight days.

• On Day 8 the plants are transported to the greenhouse and transplanted into the nutrient film technology troughs.


• They are grown until harvest on Day 33.1. Spinach seeds have inhibitors that often result in uneven germination. – Some seeds germinate very quickly,

while others are delayed for various periods.

– In nature, the variation increases the probability of survival for at least some of the seeds.

– This characteristic makes the goal of producing a uniform crop at maturity more difficult.


a. Uniform seed germination can be improved by “priming” the seeds.– Priming encourages the absorption of moisture

while removing chemical inhibitors.

b. The priming process begins by soaking the seed in 1 percent sodium hypochlorite (NaOCl) for 10 minutes to prevent disease. – This is followed by soaking the seed in

polyethylene glycol (PEG 8000, 30%) for 72 hours.

– After a rinse with NaOCl solution, the seeds are dried with a small fan for five hours.

– Between each treatment, the seeds are rinsed with reverse osmosis water.


c. Single seeds are sown in rock wool cubes or plugs of germination medium.– The rock wool cubes of medium are thoroughly

moistened with RO water and placed in the ebb-and-flood benches in the germination area.

– For the first 24 hours, RO water is used instead of a nutrient solution.

– The plants are kept in darkness for the initial 24 hours.

– The temperature is set at 68°F (20°C). – The seed trays are covered with plastic for the

first 48 hours to guarantee high humidity and to prevent drying.


d. After 24 hours, a nutrient solution is used for subirrigation. – The pH of the solution is adjusted to 5.8. – The solution is recirculated within the ebb-and-

flood system. – The plants are top watered with nutrient solution

each day.– The day temperature is set to 77°F (25°C) and

night temperature at 68°F (20°C).

e. Seedlings of good quality are transplanted on Day 8 to the pond area in the greenhouse. – They are grown until harvest on Day 33.

How are tomatoes grown by hydroponics?

• The quantity of tomatoes grown hydroponically is increasing annually.

• The most common tomatoes grown by hydroponics in the United States are beefsteak ‘Trust’, which makes up about 80 percent of acreage, and cluster ‘Tradiro’, which is becoming more popular.

beefsteak ‘Trust’,


• Cherry tomatoes are not recommended for hydroponic production.

• Careful variety selection improves the success of hydroponic production of tomatoes.

• Seed to harvest of beefsteak cultivars takes from 60 to 90 days, depending on the cultivar and growing conditions.


• Tomatoes have five main stages of growth and development.

• The germination stage extends from when a seed is sown until the seed coat breaks and the roots emerge.

• The seedling stage extends from when the seed coat breaks and the roots emerge until the seedling is transplanted into growing medium.


• The vegetative stage extends from when the seedling is transplanted into growing medium until the first flower opens.

• The early fruiting stage extends from when the first flower opens until the first fruit is picked.

• The mature fruiting stage extends from when the first fruit is picked until the termination of the crop.


1. During the germination stage, single tomato seeds are sown directly in rock wool cubes or plug trays filled with germination medium.a. Tomato seeds should be sown 1/4 to 3/8 inch deep and lightly covered with a thin layer of vermiculite. – Another option in covering the seeds is to use clear plastic

to conserve moisture at the surface. – If the cubes or plugs are to receive direct sunlight, avoid

the use of plastic, as the temperature may get too hot for good germination.

– The plastic must be removed once seedlings emerge.


b. Day and night air temperatures should be set between 75° and 79°F (24° and 26°C). – The temperature of the growing medium should

be maintained between 73° and 79°F (23° and 26°C).

– The relative humidity should be between 75 and 100 percent.

c. Overhead watering is the most common method used for germinating seeds. – Ebb-and-flood systems are also effective. – Water pH should be between 5.5 and 6.0.


d. In northern latitudes, supplemental light may be required for strong growth of seedlings. – This is especially true during

winter months. – Supplemental light should be

provided for 14 to 18 hours per day.


e. Soilless germination mixes may have enough nutrients for germinating seedlings to eliminate the need for any additional nutrients for the first few weeks of growth. – Seeds sown in an inert medium, such as rock

wool or oasis, require irrigation with a solution that has a low nutrient concentration (1,800 EC).

f. Germination usually occurs within one week of seeding.


2. During the seedling stage, day air temperatures should be set between 75° and 79°F (24° and 26°C). – The temperature of the growing medium should be

maintained between 73° and 79°F (23° and 26°C). – Night air temperatures should be dropped to 66° to 68°F

(19° to 20°C). – The relative humidity should be between 70 and 80

percent. – The EC should be raised to between 2,300 and 2,800.

a. Transplanting of the seedlings should be done once true leaves appear.b. This is 12 to 14 days from the time of seeding.


3. During the vegetative stage, day air temperatures should be set between 75° and 79°F (24° and 26°C), and the growing medium temperature should be maintained between 68° and 75°F (20° and 24°C). – Night air temperatures should be kept at 66° to

68°F (19° to 20°C). – The relative humidity should be adjusted to

between 60 and 80 percent. – The EC should be between to 2,300 and 2,800.


4. The early fruiting stage should see day air temperatures between 75° and 79°F (24° and 26°c), and the growing medium temperature should be maintained between 68° and 75°F (20° and 24°C). – Night air temperatures should be kept at 66° to

68°F (19 to 20°C). – The relative humidity should be adjusted to

between 60 and 80 percent. – The EC should be in the range of 2,300 to

2,800.


5. The mature fruiting stage should see day air temperatures between 75° and 79°F (24° and 26°C). – The growing medium temperature should be

maintained between 68° and 75°F (20° and 24°C).

– The night air temperatures should be kept at 66° to 68°F (19° to 20°C).

– The relative humidity should be adjusted to between 60 and 80 percent.

– The EC should be in the range of 2,300 to 2,800.

How are cucumbers grown by hydroponics?

• Three distinct types of salad cucumbers are grown in greenhouses: the standard American slicer, the Japanese, and the European greenhouse.

• The most widely grown cucumber in hydroponics is the European greenhouse type.


• This dark green seedless cucumber is mild in flavor and has a thin, tender skin that does not require peeling.

• Cucumbers require different fertilization and climate than tomatoes, but they are grown in the same substrates and are trained to grow upright.


• All European greenhouse cucumber varieties produce fruit without pollination. – They are gynoecious in flowering habit, which

means they produce only female flowers.– Fruit develops without the need for pollination. – If pollen is transferred from male to female

flowers, seeds will develop, distorting fruit shape and making the fruit unmarketable.

• Under optimal growing conditions, greenhouse cucumbers produce fruit 60 to 70 days after seeding.


1. Cucumber seeds should be planted about ½ inch deep. – The medium should be thoroughly watered after seeding. – Trays or pots should be covered with a sheet of clear

polyethylene to prevent moisture loss and maintain more uniform soil temperature.

– Given a warm temperature of 84°F (29°C), cucumber seeds will germinate within two to three days.

– As soon as seedling emergence begins, the polyethylene sheet should be removed.

– The germination rate of cucumbers is close to 100 percent. – For this reason, it is practical to plant one seed per

container. – Greenhouse cucumbers are ordinarily started from

transplants, but direct seeding in the finish container may also be practical.


2. Never allow cucumber transplants to become stressed for water or nutrient. – It is recommended that a complete nutrient

solution be applied whenever irrigation is required.

3. Temperatures should be maintained between 73° and 81°F (23° and 27°C) during the day. – For best production, night temperatures should

drop no lower than 64°F (18°C).


4. The bag culture hydroponic system is preferred by many cucumber growers.– One cucumber plant is placed in each bag, with

bags spaced 16 to 18 inches apart in the row.

5. A complete nutrient solution is trickled into the bag several times a day, depending upon temperature and plant size. – Usually the amount needed is 1 to 4 quarts per

day per plant.

Review/SummaryReview/Summary

•What is involved in the production of hydroponically grown foods?

•How are lettuce and spinach grown by hydroponics?

Review/SummaryReview/Summary

•How are tomatoes grown by hydroponics?

•How are cucumbers grown by hydroponics?

horticulture science lesson 41 growing crops by hydroponics

Documents

production of lettuce

hydroponics slide

cucumber production

aggregate hydroponic

aggregate system

type of aggregate culture

green peppers

system of choice