Choosing a Hydroponic Medium
Choosing the proper hydroponic medium is the most important factor for a successful hydroponic garden. All mediums react to a fertilizing program differently, and the cost of mediums varies dramatically. Some local materials (e.g. fir bark, wood chips, small stones, and coconut fibers) are available locally for a cheap price. Most large-scale hydroponic farms use large quantities of local materials to keep the costs down, but a hobbyist may get better yields from commercial products such as clay, rockwool, or sterilized soilless mix that is cheap and convenient for smaller gardens. For a hobbyist, purchasing a hydroponic medium (e.g. rockwool) from the local garden shop may be a cheaper (and better quality) solution than tracking down a free medium.
For any medium, it is safe to feed for 3 to 6 days, then flush for 1 day with plain. An option with flushing is to use plain water and 1 to 2ml of hydrogen peroxide to defend against pests in the root zone. A grower can flush throughout a plant’s life cycle, until harvest is within two weeks. Two weeks prior to harvest, growers often flush out the medium with plain water, a clearing solution followed with plain water, or a low PPM solution (i.e. 0 to 400PPM) to get maximum flavor.
Perlite compacts and should stand in a container of water for about a half hour. Fine particles of perlite will sink to the bottom of the water. The floating perlite is useful. The bottom of the barrel can go into compost or garden. Perlite is a good medium, but it does not cling onto elements. Therefore, plants must be well fed.
Clay floats, and should be soaked or sprayed until the water running through it becomes clear. Rinsing clay is similar to washing rice until the water runs clear. Clay is negatively charged and attracts positive ions such as calcium and potassium. Soaking rock-like mediums such as clay in water and 35% hydrogen peroxide (i.e. 2 to 5 ml per gallon of water) helps to sterilize the medium from any potential diseases. Sun heat helps sterilize mediums too.
Careful Alert: Perlite and other mediums can clog the feeding system and prevent the solution from pumping in or draining. All screens and filters may need a periodic cleaning and the pump should have panty hose (if used) cleaned during a reservoir change.
All mediums (except disposable mediums like rockwool) can be reused if all roots are removed from the medium, and medium is sterilized between crops. For example, clay, soilless mix, and round stones can be used indefinitely. Mediums can safely be sterilized with an application of 35% hydrogen peroxide (approximately 5 ml per gallon of water). Most mediums such as perlite can be composted or used immediately to improve soil. For example, broken down wood chips can go into compost, while perlite and soilless mix can go directly into the garden.
Mediums should be cleaned as soon as a crop is completed to avoid molds. Molds often build up while a moist medium (e.g. clay) sits unused. If necessary, a citrus cleanser can be used to clean medium so that all molds and waxy buildup are removed. After the citrus cleanser is applied, the medium should be rinsed with plain water to remove the soap-like bubbles. A little leftover cleanser in the medium will not harm the plants.
Reusing Soilless Mix
When the indoor or outdoor crop is finished, soilless mix can be sterilized with calcium peroxide so that the medium can be reused to grow more crops. This is beneficial, because after each crop is done, the grow mix retains its investment value, since it can be reused indefinitely. Only new fertilizers need to be added for each additional crop. Chemical fertilizers can be applied a little heavier in areas of adequate rainfall because the mix will get a natural flush.