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Horticulture Science
Lesson 41
Growing Crops by
Hydroponics
Interest Approach
Bring 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 Objectives
•Prepare an overview of the
production of hydroponically
grown foods.
•Describe the production of
lettuce and spinach by
hydroponics.
Student Learning Objectives
•Examine the hydroponic
production of tomatoes.
•Discuss the application of
hydroponics in cucumber
production.
Terms
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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 highquality products.
– Those products can be sold
locally, even in small
amounts.
What is involved in the production of
hydroponically grown foods?
• 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.
What is involved in the production of
hydroponically grown foods?
• 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.
What is involved in the production of
hydroponically grown foods?
• 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.
What is involved in the production of
hydroponically grown foods?
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.
What is involved in the production of
hydroponically grown foods?
What is involved in the production of
hydroponically grown foods?
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.
What is involved in the production of
hydroponically grown foods?
• 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.
What is involved in the production of
hydroponically grown foods?
• 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 fieldgrown 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.
How are lettuce and spinach
grown by hydroponics?
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.
How are lettuce and spinach
grown by hydroponics?
• 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
How are lettuce and spinach
grown by hydroponics?
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.
How are lettuce and spinach
grown by hydroponics?
How are lettuce and spinach
grown by hydroponics?
• 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.
How are lettuce and spinach
grown by hydroponics?
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.
How are lettuce and spinach
grown by hydroponics?
• 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.
How are lettuce and spinach
grown by hydroponics?
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.
How are lettuce and spinach
grown by hydroponics?
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.
How are lettuce and spinach
grown by hydroponics?
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).
How are lettuce and spinach
grown by hydroponics?
• 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.
How are lettuce and spinach
grown by hydroponics?
• 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.
How are lettuce and spinach
grown by hydroponics?
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.
How are lettuce and spinach
grown by hydroponics?
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 ebband-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.
How are lettuce and spinach
grown by hydroponics?
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-andflood 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’,
How are tomatoes grown by
hydroponics?
• 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.
How are tomatoes grown by
hydroponics?
• 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.
How are tomatoes grown by
hydroponics?
• 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.
How are tomatoes grown by
hydroponics?
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.
How are tomatoes grown by
hydroponics?
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.
How are tomatoes grown by
hydroponics?
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.
How are tomatoes grown by
hydroponics?
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.
How are tomatoes grown by
hydroponics?
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.
How are tomatoes grown by
hydroponics?
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.
How are tomatoes grown by
hydroponics?
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.
How are tomatoes grown by
hydroponics?
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.
How are cucumbers grown by
hydroponics?
• 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.
How are cucumbers grown by
hydroponics?
• 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.
How are cucumbers grown by
hydroponics?
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.
How are cucumbers grown by
hydroponics?
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).
How are cucumbers grown by
hydroponics?
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/Summary
•What is involved in the
production of hydroponically
grown foods?
•How are lettuce and spinach
grown by hydroponics?
Review/Summary
•How are tomatoes grown by
hydroponics?
•How are cucumbers grown by
hydroponics?