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Hydroponics is indeed the use of water as the primary nutrient medium for growing plants. However, this can be done in two ways - one with aggregate and one without. The idea of using aggregate is to provide support for the roots and to provide a better buffer against failure.
Generally speaking, while hydroponics allows one to grow plants without the right soil, or any soil at all, one downside is that these plants are more susceptible to sickness and failure. In farming, soil provides the nutrients and also acts as a buffer against intruding substances or against the lack of introduced nutrients. Without soil, hydroponically-grown plants react to environmental conditions much more quickly.
The aggregate used is either sand or gravel. The basic premise of this method involves:
Aeration System Construction (Optional)
Feed System Construction
Flooding / Feeding
Draining / Aerating
Start With a Good Foundation
To begin with, one must construct the substrate. The tank used for this must be able to provide a means of draining the water; generally speaking, drain holes at the bottom are best, because gravity provides the motive force.
The aggregate must be coarse to provide quick drainage. If using sand, look for those with grains about 1/16-inch diameter, while those working with gravel will want to look for 1/4 to 3/8 inch diameter units.
The aggregate materials must be as neutral as possible, containing no calcium
or other easily dissolvable minerals. Basalt, granite, silica gravel, and river-bottom rocks may be used. Even Styrofoam and crushed marbles have been used successfully by some hobbyists.
If required, one can build an aeration system into the substrate layer. This is not necessary for gravel substrates, but may be useful for sand-based aggregate substrates. However, the application of this aeration system must be judicious, as plants will differ in their substrate oxygenation needs. An aeration system like this can be passive (simply tubes and hoses with outlets outside the tank) or active (with a low-power air pump).
Blocking Light, Building a Feed System
An aggregate culture tank requires a cover to minimize light striking the surface of the substrate. This is a practice applied to prevent the growth of algae and other undesirable organisms. This cover must have one hole per plant, and can be constructed from plastic, foil, or even more rigid materials. The cover is not just for the top, but also for the sides if you used a transparent tank.
The feed system is used to flood the aggregate culture tank with nutritive fluid. One simple way to do this is to build a gravity-driven feed system. Simply put, connect a bucket or smaller tank to the larger tank with a hose. When not feeding, the liquid tank should be set lower.
When the nutritive fluid is prepared and the time for flooding comes, simply raise the liquid tank higher than the culture tank. You may also use pump-driven systems, which are recommended for larger applications, especially if multiple culture tanks link up to mutual liquid tanks.
Planting differs according to the actual plants you wish to cultivate. When planting, ensure that the plant will grow out through the holes prepared in the top cover.
Flood To Nourish, Drain to Keep From Drowning
Flooding the culture tank with nutritive fluid is basically feeding the plants. This should be done according to a schedule. Doing it too frequently may hamper the roots’ drying and aeration, hastening the growth of microbes. If a flooding is missed or if flooding is performed too infrequently, the plants’ growth is stunted or they may die, depending on the length of the “drought”.
Draining the tank after each flooding is necessary in order to prevent the plants’ roots from rotting. Enough of the nutritive fluid clings onto the aggregate to provide a steady flow of nutrients until the next flooding. In soil, the water drains away to the water table, but in hydroponics you will require some means of catching and disposing of the drained liquid.