By The Old House Web


Hydroponics is a procedure designed for growing plants without soil. The basic principle behind the process is that of growing plants with their roots in contact with a solution containing all the essential plant nutrients in amounts needed for optimum plant growth. Hydroponics is an intensive growing method requiring optimum light, temperature, and humidity. Hydroponics can be used to grow almost any herbaceous plant, however it is more difficult and exacting than traditional methods.

Hydroponics is advantageous in that it allows the propagation of plants in areas where suitable soil is not available for cultivation. Weeds and soil pathogens are usually not a major problem when using this method either. However, there are many drawbacks in employing a hydroponics system, including the need for specialized equipment, a factor which causes increased costs in set-up, maintenance, and operation. A Hydroponics system must be monitored regularly by persons knowledgeable about complex plant-nutrient solution interactions, demanding a high standard of maintenance. Without supervisation, a growing plant can quickly deplete a nutrient solution, or modify its pH. This severe stress will affect plant growth.

When using Hydroponics as a method of growing, sanitation must be carefully monitored, as any introduced pathogens will spread quickly. Because as a system without pathogens it has no pathogenetic antagonists, there is nothing able to check the spread of introduced pathogens.

Hydroponics does not necessarily result in better yields or quality. Plants must be spaced similar to those in soil culture to allow light penetration; each crop differs in their requirements, so an individual hydroponic system must be developed for each crop.

Water culture, when used as a hydroponic system of growth, involves growing plants in closed containers with the roots emmersed in a nutrient solution, providing total root contact with nutrients. Plants must be attached to physical supports above the solution. No light should be allowed inside the container to prevent algae growth, and aeration of the solution is essential and must be done mechanically.

For example, when using water culture to propagate an individual plant system, it is advised to use jars or bottles with stoppers and painted sides (for 1 plant or for several seedling-stage plants). Cut a hole in the jar stopper, placing the plant through the hole so roots are suspended in the solution. Pack cotton around the stem to keep it in position. Leave a narrow, unpainted strip down the side of the jar to determine the water level without removing the plant. A small scale set-up, for example, would involve the use of a painted-over aquarium in which a a sheet of Styrofoam is placed, complete with holes through which the plants are placed for support. An aquarium aerator, continuously injecting air into the nutrient solution, provides adequate aeration.

Aggregate culture as a Hydroponic system involves the use of aggregate for plant support. It is a process which is similar to the growing of plants in a peat-like medium in which various fertilizers and mineral elements have be incorporated. Some successfully-used aggregates include: sand - it is best to use fairly coarse sands, like river or beach sand. Coarse white silica is available locally. Aim for a sieve size range of 14 to 100 mesh. Only half of the volume of sand should be able to pass through a 30-mesh screen; the other half should be made of larger particles Help in choosing appropriate sand can be obtained at the local garden center. Gravel is another optional aggregate, and includes such materials as pebbles, crushed limestone or corals, silica gravel and slate chippings. Particle sizes range from 1/16 to 1/2 inch in diameter. For use in home hydroponics, a mixture of 25% coarse gravel, 30% fine gravel, 40% coarse sand, and 5% fine sand is recommended.

Vermiculite may also be used as an aggregate, and should be standard garden grade. Mixing it with an equal amount of coarse sand keeps the vermiculite from packing down and retaining too much water. If perlite is used, it should be standard grade. Because it is very lightweight, perlite should NOT be used with very large plants. When using broken bricks as an aggregate, the largest sized pieces should not be larger than 1/2 inch. All sizes of chips and dust should be mixed together and placed in a container.

All aggregates should be rinsed thoroughly with a dilute acid solution, then rinsed with water to remove contaminants. Solutions such as half-strength Muriatic acid are excellent choices for this task. Rinse aggregates once every two weeks to avoid toxic salt buildup. The water-holding capacity of aggregates differ, thus, check them frequently to maintain the right amount of water.

The concentration of minerals in the solution may be lower in an aggregate system than in a water system. In an aggregate system, new solution will be added often, and excess solution constantly leaches. A 1/4-strength HOAGLAND solution aids in good growth and productivity (See V.F.5. below).

A general aggregate set-up would include a trough containing the aggregate, with a drain at one end. A nutrient solution is poured or pumped into the trough at one end, and when the trough is flooded, the solution is drained out the other end. Using a pump and return hose, a continuous system can be developed.

When aggregate culture is employed in an individual plant container, this procedure differs. The container must be at least 8 inches deep, with drainage holes and stoppers. Fill the container with aggregate and place the plant within, standing the container in a tray to catch any seepage around the stoppers. Sprinkle nutrient solution evenly and thoroughly on top of the aggregate, then drain immediately.

When applying the nutrient solution application in an aggregate system, the frequency of the application should vary with the size and type of plant, its stage of development, its temperature, the light intensity and the water-holding capacity of the aggregate. To conserve nutrients, you may occasionally flush the aggregate with water instead of the nutrient solution. Do not let aggregate dry out so much that the leaves wilt, as this injures the plants and slows the growth rate.

The nutrient solution must contain all of the essential elements necessary for plant growth. Elements necessary, in their proper proportions, include:

nitrogen calcium manganese copper phosphorous magnesium boron molybdenum potassium sulfur zinc chlorine iron

Premixed solutions are available through catalogues, garden supply stores and fertilizer suppliers.

The nutrient solution must contain an optimum pH level, with a pH of 5.5 to 6.5. The pH level can be tested using nitrazine paper, available at pharmacies and drug stores, test kits for swimming pools, or pH test kit for gardeners. The solution must be well-aerated and water must often be added to the nutrient solution system.

As water evaporates, is taken up by the plant and is transpired, the volume of the solution is dramatically reduced, resulting in both a salt toxicity due to high salt concentration and a potential reduction in water uptake. To monitor such fluctuations, measure the electrical conductivity of the solution using a conductivity meter, found at garden centers and electronic suppliers. A higher reading on meter signifies a higher salt concentration. Take an initial reading when the solution is first mixed, then take readings at intervals. Specific salt concentrations are not discernable, so the best thing to do is keep adding water to return it to the original volume.

Solutions will need to be changed at a varying frequency; weekly for large, fast-growing plants and as little as monthly for smaller plants. One method of changing the solution involves running a very dilute solution (10% of normal) through the solution and then discarding it.

Following is a partial listing of nutrients in HOAGLAND SOLUTIONS: *In these solutions, the nutrient concentrations are adjusted several times higher than in a normal soil solution to sustain growth for an extended period of time.

Macro-elements include: Amount for 25 gal of nutrient solution Salt Grade Nutrients ............. | | provided | ounces | | | | OR | | | |level Tbsp.| -------------------|-----------|------------|------------ Potassium phosphate| Technical | Potassium, | 1/2 oz. | (monobasic) | | Phosphorous| 1 Tbsp. | | | | | Potassium nitrate | Fertilizer| Potassium, | 2 oz. | | | Nitrogen | 4 Tbsp. | | | | | Calcium nitrate | Fertilizer| Calcium, | 3 oz. | | | Nitrogen | 7 Tbsp. | | | | | Magnesium sulfate | Technical | Magnesium, | 1-1/2 oz. | | | Sulfur | 4 Tbsp. |

Microelements include:

Salt Nutrients Stock solutions (all chemical provided (1 gal of water) grade) Amt. of stock solution for 25 gal. of nutrient solution: -------- ------------|------------|-------|-------------- Boric acid, powdered | Boron | 2 tsp | 1 cup | | | Manganese chloride | Manganese | 1 tsp | 1/4 cup | Chlorine | | | | | Zinc sulfate | Zinc | 2 tsp | 1/2 tsp | Sulfur | | | | | Copper sulfate | Copper | 1 tsp | 1/4 tsp | Sulfate | | | | | Iron chelate | Iron | 4 tsp | 1/2 cup

Below is charted nutrient deficiency/toxicity symptoms:

Hydroponically grown plants are sensitive to nutrient imbalances:

------------------- |Deficiency symptoms| ------------------- NITROGEN | stunted growth and light or chlorotic foliage. | PHOSPHOROUS| stunted, very dark green foliage; lower leaves | may become yellow between veins; monocots have | purple veins. | POTASSIUM | lower leaves with interveinal chlorosis; | browning leaf edges; brownish mottling. | CALCIUM | tip of shoot dies; interveinal chlorosis on | on upper leaves. | MAGNESIUM | lower leaves with interveinal bleaching or | chlorosis and dark green veins; leaf margins | may curl; leaves eventually die. | SULFUR | light green upper leaves with veins lighter | than surrounding tissue. | IRON | upper leaves develop interveinal chlorosis | with green veins. | MANGANESE | interveinal chlorosis of upper leaves; veins | have wider green bands; upper leaves may have | necrotic spots. | COPPER | veinal chlorosis starting in the middle leaves;

| a few leaves suddenly wilt and die and then a | few more higher up, etc. | ZINC | malformation of leaves-leaves become asymmetric. | BORON | dieback of shoot resulting in witch's broom | effect; flowers are deformed when open; stems | and petioles become brittle.

----------------- |TOXICITY SYMPTOMS| -----------------

NITROGEN | long internodes; crispy stem. | IRON | dark leaf edges. | MANGANESE| dark brown leaf veins; also iron deficiency | symptoms because too much manganese inhibits | iron uptake. | ZINC | copper deficiency symptoms. | BORON | necrosis of leaf edges.

Go To Top of File               Main Page for this Data Base

Search Improvement Project