INTRODUCTION TO HYDROPONICS

"Hydroponics" literally means "water works". It is a method of growing plants in a water/nutrient rich solution, without soil. Although in theory any plant could be grown hydroponically, in practice hydroponic gardening is usually reserved for exotic plants and flowers, or for "greenhouse" style vegetables, such as lettuce, tomatoes, peppers, cucumbers, melons and culinary herbs.

With hydroponics, plants can be grown in a completely controlled environment, free from soil born pests and diseases. By carefully monitoring nutrients, light levels and temperature, phenominal yields of high quality, delicious produce can be obtained, without using dangerous herbicides or pesticides. Therefore, hydroponic gardening is gaining popularity for both commercial and home gardening applications around the world.

HYDROPONICS IN EDUCATION

Hydroponics also has an important place in the classroom. Experimenting with hydroponics helps students better understand how plants grow. For example, by withholding certain nutrients from the hydroponic solution, students can observe first hand how plant growth is affected, then take steps to correct the deficiencies. Other experiments can be done with water quality, lighting, temperature and humidity control, and even carbon dioxide levels. In short, a hydoponic garden is a practical way for any school to set up an excellent botany lab in a controlled environment.

To better understand how hydroponic gardening works, lets review the basics of plant growth.

BASIC LIFE PROCESSES

Plant metabolism is fueled by a process called photosynthesis, whereby water and carbon dioxide are converted by energy from the sun into sugars for use by the plant. During photosynthesis,12 molecules of water and 6 molecules of carbon dioxide are changed by light energy into one sugar molecule, with 6 molecules of oxygen and water left over to be respirated by the leaves.

Water and minerals are absorbed by the root system. In a soil medium, minerals are leached from the rock particles and from decomposing organic matter. The root hair cells, found on the root tips, absorb water and minerals into the plant in the form of ions, tiny electrically charged particles. Cortical cells throughout the root system then transfer the water and mineral ions deeper into the roots via interconnecting cell walls and protoplasm. The endodermal cells surrounding the root veins regulate the flow of minerals and water. Upon demand by the plant, the water and minerals are absorbed into the root xylem, where they are transported upward into the plant.

The shoot system consists of stems and leaves. Xylem, in the veins of the plant, transports water and minerals to chloroplasts in the leaf cells, where they combine with carbon dioxide from the air. Chlorophyll (the green pigment in plants) uses light energy from the sun to convert the water and carbon dioxide into sugars called photosynthates. Excess oxygen and water are respirated from the leaves, and the photosynthates are transported throughout the plant by phloem.

Some of these photosynthates are used for plant growth, reproduction and repair, and the rest are stored in the roots, stems and fruit as sugar. It is these stored sugars which, in food crops, are edible.

Hydroponic gardening strives to optimize the nutritional and environmental conditions for plant growth in a controlled system, thus providing optimal yields.

PROPAGATION

Hydroponic gardening starts at the propagation stage. One of the most popular hydroponic growing mediums is Rockwool, a fibrous material with a high air and water holding capacity. Rockwool propagation blocks are first soaked with a nutrient solution, then the seeds are sown directly into the medium. A seed coat can also be applied, promoting early germination and strong initial growth.

Cuttings can also be propagated in Rockwool. The cuttings are simply dipped in a protective rooting gel such as Clonex. Special rooting hormones, nutrients, and antimicrobial agents in the gel help the root system get started.

Once the seedlings are well rooted, the Rockwool blocks are placed on growing slabs and are fed a nutrition solution through a dripper. The roots will grow horizontally through the slab during the plants complete growing cycle, and no transplanting is necessary. Since Rockwool provides such excellent drainage and root aeration, it is virtually impossible to overwater and kill the young plants.

More about propagation

HYDROPONIC SYSTEMS

There are many hydroponic systems available for commercial and home use. For vine crops, most commercial growers prefer the Rockwool medium in a continuous drip, recirculating system. The Rockwool slabs are placed on a flat surface with individual emitters at each site to irrigate each plant. Troughs run underneath the slabs to catch the nutrient solution and return it to the reservoir. A submersible pump in the reservoir continuously re-irrigates the slabs and the recirculation process continues.

Another popular system uses an "ebb and flow" style of recirculation, shown here in the "Baby Bloomer", table top version. The plants are anchored in a Perlite or Vermiculite medium. Volcanic perlite is an inexpensive material, with good capillary action and aeration properties. Perlite is often mixed with vermiculite, a spongy material that tends to retain nutrients, while providing excellent aeration for the roots. In an ebb and flow system, the nutrient solution is contained in a reservoir underneath the tray. A timer clicks a pump on, raises the solution to moisten the roots, then recedes back down. The process is repeated three or four times a day.

Aeroponics, a system in which the roots are suspended in air, is another system gaining in popularity. Phenominal root growth is made possible, with excellent results to the plant. For example, lettuce plants can be rooted in web pots and fitted into individual holes. A sprinkler creates a mist chamber, and the roots grow directly in the highly oxygenated nutrient solution. NASA and other research facilities are doing extensive experimentation with such systems.

More about Systems

NUTRIENT SOLUTIONS

Precise nutrient control is a major advantage with hydroponics over soil based growing. Some soils have nutrient deficiencies, but once fertilizer salts are added, there is no easy way to change or reduce their concentrations. Hydroponics (on the other hand) makes nutrient manipulation easy.

Plants require 16 essential elements to grow and reproduce.
Oxygen, carbon, and hydrogen come from water and air and are essential to photosynthesis and sugar production. These elements account for more than 95% of a plant's dry weight. The other 13 essential elements are minerals, and are provided in the hyroponic solution.

Macroelements, those elements used in greatest quantity, include:

Nitrogen, a critical component of vegetative growth.

Phosphorus, and Potassium, especially important during flower and fruit production.

Calcium, for strengthing the stems and shoot system.

Magnesium, the central element of chlorophyll, essential for photosynthesis.

Sulfur, present in some amino acids and vitamins.

Microelements, or trace elements include:

Iron
Manganese
Boron
Zinc
Copper
Molybdenum, and
Chlorine

Though used in smaller quantities, microelements are still "essential elements" needed for photosynthesis and growth; without them the plant will die.

Most commercial nutrient solutions come in A and B mixtures. The A mixture is measured and added to the water first. The reservoir is then filled almost to full and the B mixture is added. A and B mixtures are kept separate in their concentrated forms to prevent chemical reactions that could decrease the effectiveness of some nutrients. Once dilluted in water, however, the elements maintain their balance.

There are also "Grow" and "Bloom" nutrient solutions. Research shows that a plant requires more nitrogen at the beginning of its growth cycle, so a nitrogen-rich "grow" formula is used. Once flowers appear, the plant generally requires more phosphorus and potassium. So the "grow" formula is flushed from the medium, and the "bloom" formula is added. By regulating grow and bloom nutrients, more of the plants energy can be put into fruit production at the appropriate time.

More about nutrient solutions

pH REGULATION

Just adding plant food to the water isn't enough. The pH levels of the solution should be monitored daily to insure optimal utilization by the plant. pH is the acidity or alkalinity of the nutrient solution. A pH of 7 is neutral, under 7 is acidic and over 7 is alkaline. The ideal pH level for absorbing nutrients by the plant roots is between 5.8 and 6.4, or slightly acidic.

pH can be measured by using water test kits. The solution is placed in the holder and the test chemical is added. By comparing the colors in the windows, an accurate reading can be made.

If the pH is too high, (shown by a bluish color), adding a solution with nitric or phosphoric acid will bring it back down. If the pH is too low, (shown by a redish color) a solution with potasium hydroxide will bring it back up. For most plants, a pH balance of 6.0 is an ideal target.

ELECTRICAL CONDUCTIVITY

The EC, or electrical conductivity, of the solution is also important for plant growth. Distilled water has an EC of about zero; it doesn't conduct electricity. The higher the concentration of minerals in the water, the higher the conductivity.

A conductivity pen can be used to test EC. An EC range of 1.5-3.5 Mho (millihoms) is generally desireable. A low EC reading means a slightly dilute concentration. Lower to middle levels of EC promote plant growth, and should be used in the rapid growth stage. While higher EC levels suppress plant growth and should be used during the fruit production stage.

If the EC level is too low, simply add more nutrient solution to the water. If the EC gets too high, especially on hot days, add more water to the reservoir. Since plants use different nutrients in varying degrees, the entire nutrient solution should be replaced periodically to insure that the proper mineral balance is maintained.

HORTICULTURAL LIGHTING

Since environmental conditions regulate the rate at which plants take in nutrients, proper lighting is very important to successful hydroponic gardening. Visible light covers the full spectrum of colors. At the vegetative growth stage, plants prefer the blue end of the spectrum, while at the flowering stage, plants prefer the red end of the spectrum.

The two most common horticultural lights are Metal Halide (MH) and High Pressure Sodium (HPS) lamps. Metal Halide lights provide both the red and blue ends of the spectrum. A phosphorus coated MH light tips the scale toward the red end of the spectrum, good for general purpose growing. A clear MH lamp tips the scale toward the blue end.

High Pressure Sodium lamps are strong in the yellow, orange and far red range of the spectrum. They are rarely used alone, because their lack of blue light will make plants tall and spindly. But when used with uncoated Metal Halide lamps, a winning combination is achieved. The MH lamps provide blue light for plant growth, and the HPS lamps provide the far red light for fruit and flowering.

Son Agro is a special kind of HPS lamp with a 30% increase in the blue end of the spectrum, making it an ideal single source lamp from seed through harvest.

For even light distribution, a track system can be used. This system is programmed to pause at the ends of its travels so that the plants at the end of the row get the same amount of light as those in the middle. Another lighting system uses a carousel. MH and HPS lamps are alternated to give the plant a full growth spectrum.

More about horticultural lighting

TEMPERATURE AND ENVIRONMENTAL CONTROL

Temperature control is also important. If the temperature falls too much during the night, condensation on the plants can spread fungus and plant disease. Too much heat, on the otherhand, can inhibit the transpiration process and stress the plant. A good heating and ventillation system will help control temperature and maximize the productivity of the plant. Carbon dioxide supplementation is also beneficial. Provided that there is enough light available, increased carbon dioxide can stimulate the plant to flourish and grow at higher temperatures.

Special devices, such as this negative ion generator, can also be added to the system. By filtering out pollutants such as bacteria, fungi and mold spores, while saturing the environment with negatively charged ions, greenhouse trials have shown tremendous results. For example, tomato plants exposed to a high density of negatively charged particles resulted in faster growing, earlier maturing, higher yielding tomato plants, with higher concentrations of vitamin C and minerals.

Hydroponic gardening is extremely flexible. By adding simple timers and flow valves, greater automation can be achieved, making it possible to leave the system unattended for weeks at a time. Further automation can be achieved by adding special monitors and feedback devices, making complete computer control possible!

Whether a back yard hobbiest or a large commercial concern, hydroponic gardening is the way of the future for environmentally controlled agriculture.

SUMMARY

Lets summarize some of the most important benefits of hydroponics:

With hydroponics, higher yields can be achieved in a smaller space.

Hydroponics is environmentally friendly, efficiently recycling water and nutrients.

Roots need not search out or compete for nutrients in the soil.

Nutrients can be precisely controlled and are immediately available to the plant.

Soilborn pests and diseases are eliminated.

Weeds are eliminated.

Plants are healthier and reach maturity faster.

Automation is possible, reducing labor costs.

Hydroponically grown plants are nutritious and taste good.