AGRICULTURAL EXTENSION SERVICE
Hydroponic Culture of Vegetable Crops
J. G. STOUT and M. E. MARVEL
Fig. 1.-Commercial gravel culture hydroponic facility producing tomatoes.
This facility has ridge and furrow plastic greenhouse cover.
Hydroponic Culture of Vegetable Crops
J. G. STOUT and M. E. MARVEL1
Hydroponic culture is a method of growing plants without
soil. The name itself implies that the plants are grown in water.
Actually, the nutrients are supplied in water solution but the
plants may be suspended in water or they may be produced with
roots in sand, cinders, or gravel.
Fig. 2.-One type of small home
unit suitable for use by amateurs. -
I --- OF
S E TO OE 5 GAL. CAN OF
The elimination of soil as the culture medium also eliminates
problems such as weed control, tillage, irrigation and the neces-
sity for growing cover crops or adding manures for organic
matter. But for each problem eliminated another is created.
As a result, hydroponic culture is not the easy and simple method
it is often pictured to be. It is a highly specialized method of
culture. Successful operators must be highly skilled farmers
and trained technicians.
1 Dr. Stout is a former professor of horticulture in the University of
Florida College of Agriculture; Mr. Marvel is Assistant Extension Vegetable
If you are to be successful at vegetable culture by hydro-
ponics you must carefully observe many details. While the pro-
cedures to follow in producing crops without soil are quite well
established, following them does not automatically insure finan-
The investment in tanks, beds, pipings, pumps and equip-
ment for protection against winds and cold may amount to con-
siderably more than $1.00 per square foot of growing area. It
is necessary to obtain maximum yield over a relatively long sea-
son and to sell at reasonable prices in order to make a profit.
Even the most skillful operators are not always able to secure
this production, or highest prices. The crops must be of high
quality to sell readily at satisfactory prices.
It is unlikely that a commercial hydroponics establishment
can compete profitably with field-grown crops unless the products
have a ready market at prices well above those of regular farm
While you may employ either the water-solution method or
a sand, cinder, or gravel system, the gravel type of culture is
used almost entirely in Florida. The information on methods
and descriptions of equipment as given here apply primarily to
the gravel culture system.
CONSTRUCTION OF BEDS
Crops are grown in beds which are really shallow tanks or
troughs that serve as the standard type of container for the
gravel. If there are several of these beds, they should be set
up in series at the same level and of similar size.
These beds should be about 3 feet wide and any convenient
length, though 100 feet is common. Usually these beds are made
of poured concrete with sides about 8 inches high and with a
V bottom so the center is 11 or 12 inches deep. This permits an
arrangement whereby a half-tile or similar device through the
center of the bed will feed or drain the solution rapidly from
one end of the bed to the other. There must be a pipe connection
to the lowest point in the V at one end of the trough with little
slope toward that end. It is very important that the slope be
precise, with no low areas from which solution will not drain.
The nutrient solution can then be pumped into the trough
through that pipe and will drain out again when the pump has
been shut off.
Fig. 3.-Another type of small home unit suitable for use by amateurs.
Gravel or cinders for the bed should be fairly uniform in tex-
ture, about 1/2 to 1/4 inch in diameter, and washed. If you use
sand, it should be coarse and it also should be washed. Beds
should be filled to within 1 inch of the top. Concrete beds should
be coated on the inside with a high grade asphalt paint. Pipes
or other metal fittings should be of plain iron or plastic. Do not
use galvanized pipe, since dissolved zinc from the galvanizing
will cause trouble in the nutrient solution.
Depending upon the kind of crop to be grown, supporting
structures may be necessary to hold up the plants, for example,
tomatoes or cucumbers. Plants loaded with fruit are heavy.
With the usual number of 100 plants per row, substantial sup-
port is necessary. Do not attach supports to ends of beds be-
cause weight of plants may crack concrete and cause leaks.
Customarily two rows are grown in beds three feet wide.
All supporting wires are suspended from overhead supports
attached to posts or pipes that are spaced at intervals alongside
Use none but the best varieties and plants, produced in dis-
ease-free soil, sand or vermiculite and six inches or more (in the
case of tomatoes) high before planting. Thoroughly work the
media in the seedling flat with water so there will be as little
injury as possible to root systems in transplanting. Before
planting in the gravel, rinse off the soil or other material which
clings to the roots when the plants are dug. You may start
plants right in the bed if desired, and in thinning, you may
transplant elsewhere the plants that are removed.
No one nutrient solution is superior to all others. Several
can be used with much the same degree of success. Often
growers prefer to buy the ready-mixed chemical ingredients
for the solution, thereby avoiding the labor and difficulties of
mixing. The solutions are not difficult to mix and will cost con-
siderably less than ready-mixed salts. Here's an example of
one nutrient solution mixture that has given good results:
Pounds per 1,000
Gallons of Water
Magnesium sulfate (Epsom salts) .............. 2
Monocalcium phosphate (good grade) .......... 2
Potassium nitrate ......... ......... ... .....- 4
Ammonium sulfate ............... ..........-..-... ... 1
Calcium sulfate (agricultural gypsum) ....... 13
The above chemicals provide only the major elements and a
solution of micro or minor elements is needed. These can be
provided by the following combination added to the above list.
Amounts per 1,000
Gallons of Water
Iron sulfate copperass) .............................. 4 ounces
Manganese sulfate .....................-....-............. ounce
Copper sulfate (blue vitriol) ...................... /s ounce
Zinc sulfate (zinc vitriol) ............................. %/ ounce
Sodium tetraborate (borax) ....................... 3 ounces
These chemicals are often mixed in larger quantities in con-
centrated form and kept on hand so the proper amount, in solu-
tion, can be added to the solution tank when a fresh mixture is
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Fig. 4.-Side view of hydroponic facility showing nutrient solution being
pumped into beds and spray boom attached to permanent installation. To-
mato plants had been growing for six months and had been attacked by
leaf miners and diseases but were still producing.
The primary requisite of any nutrient solution is to secure
and maintain a proper balance between total concentrations and
proportions of the various chemicals in solution. Requirements
50'- 0" 1-6" 50'-0" VARI E
2" SLOPE C C' 2" SLOPE
__ L-pRAIN TILE c
"- ..... ... ...... I rO PUM
I ,t---- .. ... .... ... .... ...
DRAIN & VALVE
FOR RAIN WATER-
I- -H NOPE L-
SCALE = 1/16"= I'-0"
FILL UP TO I
3'- 0" C2"
1/2 of 4"
DRAIN TILE 8
SCALE= 3/4 I'-0"
Fig. 5.-Detailed layout for a commercial hydroponics facility;
I' I 1
50'- 0" -v 50'- 0"
S-, 2" SLOPE 2" SLOPE
[S l^- ----^ l-----.-:^
I __ -
S ANPE I*-DRAIN a VALVE FOR
30'- SLPERAIN WATER
BYPASS CHANNEL-- BED-
'rELEV: 98'-9"1" SLOPE 2" SLOPE
SI-0" 2" 1-6" .2"
GRAVEL )f H ASPHALT COATING
DRAIN TILE ---- --- 4
SCALE= 3/4"= I'- "
LAYOUT FOR HYDROPONIC FACILITY
drawing by Extension Agricultural Engineering Department.)
for potassium, calcium, magnesium, nitrogen, phosphorus, and
sulfur are relatively large for all plants. They need smaller
quantities of iron and only traces of manganese, boron, copper,
zinc, and other elements.
When you use cinders or gravel in the beds as a growing
medium, they may contain a wide variety of minerals and the
micro or minor elements may not be necessary. Also, if you
use commercial fertilizers in place of the pure chemicals in mak-
ing the solutions, impurities may be adequate in some cases to
supply the same minor elements. In other cases impurities may
be present in sufficient concentration to cause injury.
Commercial fertilizers may contain insoluble material. Pos-
sibly one-fourth of the fertilizer may not dissolve. Always use
the highest analysis fertilizers available or the most soluble
fertilizer salts when making up the solutions. The higher grades
of magnesium sulfate, potassium sulfate, potassium nitrate, and
ammonium sulfate appear to contain fewer impurities and gen-
erally none that are harmful. Fertilizer grades of phosphate
salts may contain fluorine in amounts higher than 1%. Do not
use any fertilizers with more than 1% fluorine.
Prepare solutions by dissolving the ingredients in smaller
quantities of water and then adding these to the solution tanks.
Some of the elements will be absorbed out of the solution by
plants. At the same time, there is considerable loss of water
through transpiration and evaporation. These processes tend
to change the concentration of elements in the water and make
the solution stronger or more concentrated. The chief danger
is that of creating an unbalance. Water, of course, must be
added frequently to replace that which is lost. The tendency,
therefore, is for the nutrient solution to gradually become less
concentrated or weaker.
The acidity or alkalinity, usually measured by pH of the
nutrient solution, affects the availability of some of the nutrient
elements. For best results this should be kept between pH 5.5
and about 6.5. There is no appreciable amount of buffering
capacity to the nutrient solution, so the pH must be checked
frequently. If necessary, sulfuric acid used to make the solution
more acid (lower the pH). A dropper bottle of .04% brom cresol
green, a porcelain test plate or glass vial, and a chart which
shows the color of the solution at different pH's, is a good com-
bination to have at hand. Then it is a simple matter to deter-
mine the degree of acidity and to correct it when necessary.
BUSHEL BASKET BEAN HAMPER 5 GAL. CAN
Fig. 6.-Individual plants are grown in different types of containers with wood shavings.
If the weather is warm and plants are growing rapidly it
may be necessary to empty the solution tanks and replace with
new solutions as often as once a month, sometimes oftener. The
used solution is still relatively high in some nutrient elements
and can be used to advantage on nearby gardens, lawns, or plant-
ings. The nutrient solution mentioned is relatively low in ni-
Plants may be able to use somewhat more potassium nitrate
and ammonium sulfate in warm weather because of more rapid
growth. Doubling the amounts of these compounds is often
desirable. The same can be said for the other chemicals under
those conditions. An increase of 30 to 50% in concentration of
all materials in the solution is often justifiable.
OPERATING THE SYSTEM
The entire hydroponics system is relatively simple to operate
and may be made at least semi-automatic. The quantity of so-
lution in the tank should be just sufficient to bring the water
level up to within 1/2 to 1 inch of the top of the gravel in the beds.
A centrifugal pump of sufficient capacity to fill beds in one-half
hour is generally best for forcing the solution into the beds.
It should be of sufficient capacity to drain the system for clean-
ing. In cool weather, you may pump only once a day, but in
warm, dry, or windy weather, it may be necessary 2 or 3 times.
You can install a time clock which will start and stop the pump
automatically. With a centrifugal pump, you may allow the
solution to flow by gravity through the pump back into the tank.
How often to operate the pump is simply a matter of keeping
the gravel or cinders wet enough so plants always have an ad-
equate supply of water. This requires judgment on the part of
the operator and no automatic device has been developed to take
the place of personal inspection. A good indication of need for
repeating the pumping operation is wilting of the plants.
INDIVIDUAL PLANT METHODS
If space is not available or if you do not desire to invest in
tanks for hydroponic gardens, plants such as tomatoes, eggplant
and pepper may be grown in bushel baskets, five-gallon cans,
or smaller plants may be grown in still smaller containers.
Punch holes in the bottoms to allow adequate drainage. Fill
the container with sand, soil, sawdust, shavings, or well-rotted
You may use the standard hydroponic fertilizer solution.
If only a few plants are involved, you can make a small quantity
of solution by reducing all ingredients proportionately. For
example, a reduction to 1/10 of all ingredients would result in
100 gallons of solution instead of 1,000 gallons. Apply enough
of the solution to saturate the growing medium to the bottom
of the container at each application. The frequency of applica-
tion will depend upon the temperature, growing medium, and
size of plants. However, an application once every three days
should be adequate.
Vining and tall-growing crops such as tomatoes, pole beans,
cucumbers and peas will require some type of support.
IMPORTANT CONSIDERATIONS IN DESIGN
1. The troughs or benches should all be level and at the
same height. Otherwise it will be difficult to regulate the pump-
ing operation so all benches receive the same amount of solution.
2. If you use asphalt paint for treating the concrete troughs,
etc., be sure it is of highest grade. Some highway and roofing
materials contain tars and fluxes. Avoid them. When placed
in hot water, good asphalt will not cause any discoloration and
will leave no oily film.
3. If the gravel contains considerable lime it will be difficult
to maintain the proper pH in the nutrient solution. Lime will
boil vigorously if muriatic (hydrochloric) acid is poured on it.
It is best to test the gravel with this acid to determine whether
it is objectionably high in lime content.
4. If you use cinders instead of gravel as the culture medium,
they too may contain objectionable chemicals. Most of the sub-
stances of injurious type are soluble and thorough washing and
leaching will remove them.
PROTECTION FROM FREEZING
Hydroponic gardens generally are open to the elements and
thus are subject to frost damage on occasions. This is one of
the reasons why most of the large hydroponics structures are
in the southern part of Florida where need for frost protection
is slight or infrequent.
However, with the very high investment in crop, equipment
and labor, all of which will be lost if the crop freezes, it is im-
perative that there be some protection when cold comes. It is
rarely possible to provide adequate coverings for the entire area.
It is more likely that dependence will have to be placed on heating
Smokeless oil burners are very good for the purpose except
that there is often no place where those heaters can be placed
so the intense heat will not injure nearby plants. Usually, heat-
ers around the periphery of the area are sufficient. In the larg-
est establishments, it may be necessary to leave spaces between
benches or provide a different heating arrangement. Inexpen-
sive polyethylene plastic covers may be used.
DISEASES AND INSECTS
Diseases constitute one of the most serious problems in hydro-
ponic production of vegetables. Soil-borne maladies affect nearly
all vegetable crops and the fact that soil is not used does not
eliminate these troubles. In reality the problem is magnified
because of the danger of carrying disease through the nutrient
solution and spreading it quickly to all other plants in the sys-
tem. There are no known materials which can be dissolved in
the nutrient solution which will serve to control diseases while
the crop is being grown.
Therefore, much of the difficulty in hydroponic culture comes
from the ease of disease spread and inadequacies of the control
methods which must be used.
As in all plant production, the best system is to prevent the
introduction of diseases which may be spread widely from the
initial infection. This calls for a rigorous campaign of sanita-
tion and utmost care in production of plants, handling and treat-
ing plants and spraying and other practices to make certain that
diseases are kept away from the production area.
Often it is impossible to ascertain how diseases are carried
and consequently it is impossible to forestall their introduction.
Once soil-borne diseases have been discovered in the planting,
there may be little that can be done other than to fertilize the
plants to the maxiumm and get the most out of the crop in spite
of the disease.
Leaf diseases, such as mildews, blights, leafspots, and leaf
molds, attack plants under hydroponic culture conditions much
as they do when those crops are grown in the open. Also, vari-
ous insect pests must be rigidly controlled. The spray program,
therefore, is very important and should not be slighted.
There is considerable expense for materials and equipment
and labor but it is important that the best kind of equipment
should be available for making the applications, and skilled oper-
ators should do the work. Anyone who is unwilling to give this
part of the program the attention it deserves should not contem-
plate becoming a hydroponics operator.
One nice feature of the hydroponic system is the ease with
which sterilization of the beds and tanks can be accomplished
when there is no crop in production. Solutions of powerful dis-
infectants can be circulated through the pipes, beds, and gravel
medium and will dispose of troublesome diseases which might
cause losses later. Most growers perform this sterilizing opera-
tion as a routine procedure between each two crops as a safety
measure, even though serious diseases have not been encountered.
They have found that it is good insurance against crop losses.
Sodium trichlorophenate 85% (Dowicide B) at the rate of
300 parts per million parts of water has been used successfully.
Keep the pH of the solution near 7 to prevent precipitation of
sterilant. Do this by adding 300 ppm of sodium hydroxide to
the solution of Dowicide B. Let stand for 24 hours, then drain
system and rinse with a 300 ppm solution of sodium hydroxide
and twice with clear water.
1. Bulletin 636, N. J. Agricultural Exp. Sta., Rutgers University, New
Brunswick, N. J.
2. Circular 347 revised, College of Ag., University of California, Berke-
3. Circular 152, University of Florida Agr. Extension Service, Com-
mercial Vegetable Pest Control Guide.
4. Misc. Publ. No. 173, Univ. of Maryland, Ag. Experiment Sta., Col-
lege Park, Maryland.
5. Research Bulletin 679, Ohio Agricultural Experiment Station, Woo-
6. S. C. 328, Purdue University, Agricultural Experiment Station, La-
7. Successful Gardening Without Soil, Chem. Pub. Co., Inc., 212 5th
Ave., N. Y., 1956.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director