systems will not compensate for poor growing conditions such
as improper temperature, inadequate light, or pest problems.
Hydroponically grown plants have the same general requirements
for good growth as field-grown plants. The major difference
is the method by which the plants are supported and the inorganic
elements necessary for growth and development are supplied.
Plants grow well only within a limited temperature range.
Temperatures that are too high or too low will result in abnormal
development and reduced production. Warm-season vegetables
and most flowers grow best between 60° and 75° or
80° F. Cool-season vegetables such as lettuce and spinach
should be grown between 50° and 70° F.
All vegetable plants and many flowers require large amounts
of sunlight. Hydroponically grown vegetables like those grown
in a garden, need at least 8 to 10 hours of direct sunlight
each day to produce wells Artificial lighting is a poor substitute
for sunshine, as most indoor lights do not provide enough
intensity to produce a crop. Incandescent lamps supplemented
with sunshine or special plant-growth lamps can be used to
grow transplants but are not adequate to grow the crop to
maturity. High intensity lamps such as high-pressure sodium
lamps can provide more than 1,000 foot-candles of light. The
serious hobbyist can use these lamps successfully in areas
where sunlight is inadequate. The fixtures and lamps, however,
are very expensive and thus not feasible for a commercial
spacing between plants will ensure that each plant receives
sufficient light in the greenhouse. Tomato plants pruned to
a single stem should be allowed 4 square feet per plant. European
seedless cucumbers should be allowed 7 to 9 square feet, and
seeded cucumbers need about 7 square feet. Leaf lettuce plants
should be spaced 7 to 9 inches apart within the row and 9
inches between rows. Most other vegetables and flowers should
be grown at the same spacing as recommended for a garden.
vegetables, whether grown in soil or in a hydroponic system,
will not do as well during the winter as in the summer. Shorter
days and cloudy weather reduce the light intensity and thus
limit production. Most vegetables will do better if grown
from January to June or from July to December than if they
are started in the fall and grown through the midwinter months.
Providing the plants with an adequate amount of water is not
difficult in the water culture system, but it can be a problem
with the aggregate culture method. During the hot summer months
a large tomato plant may use one-half gallon of water per
day. If the aggregate is not kept sufficiently moist, the
plant roots will dry out and some will die. Even after the
proper moisture level has been restored, the plants will recover
slowly and production will be reduced.
quality can be a problem in hydroponic systems. Water with
excessive alkalinity or salt content can result in a nutrient
imbalance and poor plant growth. Softened water may contain
harmful amounts of sodium. Water that tests high in total
salts should not be used. Salt levels greater than 0.5 millions
or 320 parts per million are likely to cause an imbalance
of nutrients. The amateur chemist may be able to overcome
this problem by custom mixing the nutrient solutions to compensate
for the salts in the water.
Plants require oxygen for respiration to carry out their functions
of water and nutrient uptake. In soil adequate oxygen is usually
available, but plant roots growing in water will quickly exhaust
the supply of dissolved oxygen and can be damaged or killed
unless additional air is provided. A common method of supplying
oxygen is to bubble air through the solution. It is not usually
necessary to provide supplementary oxygen in aeroponic or
continuous flow systems.
Nutrients. Green plants must absorb certain minerals through
their roots to survive. In the garden these minerals are supplied
by the soil and by the addition of fertilizers such as manure,
compost, and fertilizer salts. The essential elements needed
in large quantities are nitrogen, phosphorus, potassium, calcium,
magnesium, and sulfur. Micronutrients - iron, manganese, boron,
zinc, copper, molybdenum, and chlorine are also needed but
in very small amounts.
In a garden the plant roots are surrounded by soil that supports
the growing plant. A hydroponically grown plant must be artificially
supported, usually with string or stakes.