DEPARTMENT OF SOILS MIMEO REPORT NO, 59-1
FLORIDA SAWDUST FOR HOME HYDROPONICS
Seton N. Edson
Department of Soils
Florida Agricultural Experiment Stations
November 10, 1958
Department of Soils
Agricultural Experiment Station
University of Florida
FLORIDA SAWDUST FCR HOME HYDROPONICS
Seton N, Edson
Associate Professor of Soils
In the year 1860, Sachs (5) made the following statements "I
published the results of experiments which demonstrated that land plants
are capable of absorbing their nutritive matters out of watery solutions,
without the aid of soil, and that it is possible in this way not only
to maintain plants alive and growing for a long period of time, as had
long been known, but also to bring about a vigorous increase of their
organic substance, and even the production of seed capable of germination."
This marked the earliest published water culture method for growing
plants without soil. Obviously, hydroponics or soilless growth, had a
very early beginning. The only real change over the years has been in
methods and formulas. It is interesting to know that Sachs (5) germ-
inated his seed in clean washed sawdust and transplanted the young plants
in a nutrient solution. Since his studies were in plant physiology,
water culture, with pure salts, was a necessity.
In 1938, Hoagland and Arnon (2) published their bulletin on water
culture methods for growing plants without soil. A seed bed of rice
hulls, sawdust, or shavings was suspended over the nutrient solution.
The plant roots grew in the sawdust, passed through the one inch air
space, and also grew in the nutrient solution. Their technique gave
excellent results with a wide variety of plants. After it was shown by
these hydroponic methods that sawdust showed little if any decomposition
after the termination of the average growing season, then many amateur
gardeners began to use common sawdust as a medium in several kinds of
containers. Kept moist, and treated with a soluble salt solution, these
methods grew very satisfactory plants. This pleasant hobby made fast
progress in Florida in recent years because no greenhouse or expensive
protective cover were necessary.
Numerous inquiries are received each year by the University of
Florida from home gardeners for a simple hydroponic method for growing
plants. The most frequent request is for a convenient and simple means
of obtaining the necessary nutrient salts to make up one of the many
formulas that are obtainable. This imposes several important compli-
cations for the beginner, some of which he will understand and others
which may cause complete failure of his hydroponic venture. A typical
example is found in the use of some of the high analysis soluble fertil-
izers available for making liquid fertilizers.
These fertilizers must have fairly pure salts in their mixture to
attain a high analysis rating. Several of these high analysis soluble
fertilizers have had to skimp on certain essential elements to crowd
the necessary nitrogen, phosphorus, and potassium into the formula,
or they may be omitted entirely. The most common element generally
left out or reduced in amount is calcium, yet this element is essential
in a high degree. Since calcium forms few desirable soluble salts that
remain dry and stable over a period of time, it does not lend itself to
total soluble fertilizer mixtures.
Plants will not succeed in hydroponic growth if all fifteen essential
elements are not present in some form or other in the formula. To meet
this problem it was decided to use an easily obtainable 8-8-8 mixed fer-
tilizer which w uld carry a plentiful supply of calcium in the super-
phosphate of the mixture. The only additional elements added were
magnesium, potassium, and iron. Potassium was added in order to change
the 1-1-1 ratio to a 1-1-2o Other essential elements should be present
as impurities. The ratio of 1-1-2 closely parallels a few of the more
successful hydroponic formulas that have been used to date in this area.
Florida has little or no native gravel fit for a good hydroponic
medium. Sand was ruled out due to its unfavorable property of packing
plus the accumulation of algae in the pore space. Florida does have an
enormous supply of waste sawmill sawdust. This article is an endeavor
to present a choice of two simple yet satisfactory means of using saw-
mill sawa.ust and common commercial mixed fertilizer for home hydroponic
growth of vegetables. These methods are compared with each other and
with other salt formulas in order to demonstrate their feasibility.
THE HYDROPONIC BENCH
A location was selected where some afternoon shade could be expected.
Four treated posts were sunk into the ground leaving about two feet of
post exposed above ground. These were spaced about eight feet in length
and wide enough to fit six boards. Using 1" x 6" No. 2 treated boards
eight feet long, a bench was fashioned so that the six boards exactly
fitted in between the two posts (see Fig. 1), and rested on a cross
member of similar material. The sides and end were two boards high
(about 11" deep). Although this experimental bench was only one section,
or eight feet long, the length may be as long as desired.
The bench was lined with a single sheet of polyethylene plastic
with the top edge tacked down. In the water culture bench, a pipe was
fitted in the bottom to allow for draining as well as keeping a constant
level of solution (Fig. 1). The drain pipe was turned up just high enough
to keep the nutrient solution at a depth of six inches. The same pipe
can be turned down to drain the solution. One inch above the level of
the nutrient solution, a 1" x 1" wood strip was nailed along the sides
and over the polyethelyene sheeting. Similar 1" x 1" crecs member strips
at about 1 foot apart were nailed to these strips. These strips acted
as supports for random pieces of common hardware cloth. A little wood
excelsior was scattered on this hardware cloth and the remaining 4 inch
depth was filled with sawmill sawdust to the top edge of the bendh.
For the dry salt method, the cross member strips were left outi
the drain was turned down to allow free drainage at all times; the bench
was filled completely with sawmill sawdust.
THE DRY SALT CULTURE METHOD
The dry salt culture method has been briefly described by both Ellis
and Swaney (1) and Laurie (4). After the bench was filled with sawdust
as described previously, the N, P, K, Ca, and S were supplied by common
8-8-8 commerical fertilizer plus additional potassium. Mg was supplied
by mixing three ounces of common epsom salts to one pound of 8-8-8 fer-
tilizer. This also supplied additional sulfur. Iron was added by a
weekly sprinkling of a teaspoon of iron sulfate dissolved in about two
gallons of water. The remaining minor elements; i.e., Mn, B, Cu, Zn,
and Mo come with the commercial fertilizer mixture as impurities.
There is no magic formula for hydroponic plant growth. If any plant
is given the above elements in the right amounts and proportions, is free
of disease, and is exposed to sufficient light and moisture, they will
grow to their optimum size and no more. Hoagland and Arnon (2) have shown
that there is no difference in food quality if all growth requirements
The dry mixed 8-8-8 plus 3 oz. each of epsom salts and sulfate of
potash were spread at the rate of 1 to 2 Ibs. per 100 sq. ft. of area,
or about 1/2 to 1 cup per 24 sq. ft. bench. Two weeks prior to planting,
the salts were soaked into the sawdust. Following this, young tomato plants
were set in the sawdust, and cucumber seeds were planted at 10 inch spacing,
leaving a strip along each side of the bench to spread the fertilizer.
In the final experiment, twelve tomato plants and twelve cucumber plants
As the plants grew, between 1/2 to 1 cup of the fertilizer was scat-
tered on the surface and along the strip free of plants every two weeks
and was immediately washed into the sawdust with the sprinkler. Every
evening about 6 P.M. the sprinkler was turned on for about five minutes
to moisten, but not leach, the sawdust. During rainy days, no water was
needed. The surface was lightly worked to keep it from packing and to
allow good aeration of the roots.
After all of the plants became well established, iron was added every
week by dissolving about one teaspoon of crude iron sulfate in a two gallon
sprinkling can filled with water and the contents sprinkled over the grow-
ing plants. Aluminum wire was stretched across the bench at various
heights in order to support the growing plants. The plants were grown
as prescribed for ordinary spring and fall conditions of light and tem-
The only treatment for pests was a sprinkling of malathion following
directions given on the bottle and used on the plants as needed.
THE WATER CULTURE METHOD
This method has been used for many years and is described in detail
by Hoagland and Arnon (2). The culture for this technique is exactly as
given for the dry salt culture method with the exception of the fertilizer
application. In the water culture procedure, one pound of the 8-8-8 plus
3 ounces each of epsom salts and sulfate of potash is poured into a gallon
jug and dissolved in tap water(a). One ounce of this stook solution is
diluted with one gallon of tap water to make the nutrient or growing
A clean 20 gallon garbage can was set near the bench and a ready sup-
ply of the growing solution kept on hand. The water culture bench was
filled as described previously with six inches of the nutrient solution
and kept at this level for two weeks. As the plants grew, the roots soon
grew into the sawdust and on down into the nutrient solution. The surface
was kept moist with the nutrient solution from the storage can; the solu-
tion in the bench was changed every two weeks.
The only remaining care was a weekly sprinkling of iron sulfate. The
addition of one half level teaspoon of iron chelate, 10-12% Fe, to the
gallon of stock solution, was found to be a satisfactory alternate proce-
During one growing season, the Purdue Formula B (6) was used in the
water culture method in order to compare yields with the methods just des-
cribed. Yields for each of these methods were compared and are given in
Tables 1 and 2.
(a) Shake well before using.
Use 2 os. of stock solution per gallon of growing solution for well
established plants in the fall and early spring.
EQUIVALENT ANALYSIS OF THE TWO WATER CULTURE FORMULAS USED
S! ..... .. ppm _
Hydroponic Method Formula Used N P K Ca Mg pH
tater Culture Bench A Purdue B 84 35 195 100 48 6.0
Water Culture Bench B 1 lb. 8-8-8
+ 3 os.
+ 3 oz.
K K2SO4 per
128 gal. water 106 47 200 200 50 6.0
RESULTS AND DISCUSSION
Yields were accumulated and terminated at the end of 110 days of
growth. Yield data results are given in Table 2.
__YIELD DATA COMPARED
112 plants 12 plants
Hydroponic Method Formula Used Lbs. of Tomatoes Lbs. of
Dry Salt Culture Method 1 lb. 8-8-8 + 3 oz.
MgSO4.7H20 + 3 oz.
K2o04 4o 20
Water Culture Purdue B Formula 65 44
fater Culture 1 lb. 8-8-8 + 3 oz.
MgSO47'H20 + 3 oz.
K2SO4 per 128 gal.
water 60 40
The water culture benches appeared to give higher yields than the
dry salt method. This may be the result of better salt concentration
in the water culture technique. Some difficulty was experienced in
keeping the sawdust moist in the dry salt bench during dry weather
spells. Results were similar when comparing the Purdue B formula with
the formula offered in this paper. However, the simplicity of using a
common fertilizer such as an 8-8-8, which can be purchased locally, is
of major importance to the home gardener. The small expense involved
is also an immediate advantage. Although an 8-8-8 plus 3 oz, of sulfate
of potash were used in this experiment to yield a 1-1-2 ratio, an 8-8-16
or similar fertilizer should give the same results.
The 1-1-2 fertilizer was excellent for fall and early spring condi-
tions. On the other hand, the 8-8-8 fertilizer, or 1-1-1 ratio, without
the extra 3 oz. of potassium, gave better growth for tomatoes in late
spring and early summer with the warmer days and longer periods of day-
The use of sawmill sawdust and easily available commercial fertilizer
for hydroponic culture should appeal to the retired person who wishes to
grow plants without the necessity of complicated equipment and chemical
formulas, It should also appeal to the person who may have a small yard
with little space for a garden. It should have a special appeal for the
teacher looking for school projects in connection with the study of plant
growth. In any event, there is neither a waste of time nor money for
anyone who likes to grow plants.
1. Ellis, C., and Swaney, M. W. (Revised by Tom Eastwood). Soilless
Growth of Plants. 2nd ed. Reinhold Publishing Co., N. Y.
2. Hoagland, D. R., and Arnon, D. K. The Water Culture Method for Grow-
ing Plants. Cal. Agr. Exp. Sta. (Berkley) Cir. 347. 1950.
3. Kiplinger, D. C. Growing Ornamentals, Greenhouse Crops in Gravel
Culture. Ohio Agr. Exp. Sta. Cir. 92. 1956.
4. Laurie, Alex. Soilless Culture Simplified. McGraw-Hill Book Co.,
5. Sachs, Julius von. Lectures on the Physiology of Plants. Clarendon
Press, Oxford, England. 1887.
6. Yithrow, R. B., and Withrow, A. P. Nutriculture. Purdue Agr. Exp.
Sta. Cir. 328. 19L8.
HOME HYDROPONIC BENCH
(l"x6" treated boards)
3" treated posts
Drain and nutriel
sawduet ? "
. ir spoao 'IC
Six boards wide
Cross members to support !
4" mesh hardware cloth