Often, people assume hydroponics means growing plants in water, but in reality, hydroponics is a term used to refer to plant production without soil, using water and a wide range of organic and inorganic materials. Which medium you use depends on your hydroponics gardening needs. There is no soil in your hydroponics system, but your plants will still require anchoring and there are a wide range of inert materials that can be used to support plant roots. They are called ‘growing media’.
Perlite, rockwool, clay pellets, coir (from the husk of the coconut), vermiculite, sand and gravel are some common growing media. The ideal hydroponic medium provides plants with adequate support, is moisture absorbent and allows good air circulation. It should also preferably be pH neutral.
Perlite is a volcanic rock that is a fusion of granite, obsidian, pumice and basalt, obtained at very high temperatures. The final product formed by heating at high temperatures is lightweight; they are expanded glass pebbles. Perlite can be used to decrease soil density. It holds more air and less water than vermiculite. It can be used loose of in plastic sleeves that have been immersed in water.
Vermiculite is also a superheated medium that has expanded into light pebbles. It holds more water than perlite. The natural wicking properties of vermiculite mean that water and nutrients can be easily drawn from it in a passive hydroponic system. But if its good capacity for water retention hampers air circulation, you can lower vermiculite’s water retention properties by mixing it with another medium.
Rockwool is the commonest medium known to hydroponics. It is cheap, inert and simple to use. It works in both free drainage and re-circulating hydroponics systems. It is made from molten rock that is spun into thin clusters of fibre. Hence it is conducive to capillary movement but not degraded by microbiological activity. It is a high density medium, and that improves the dispersal of nutrients and moisture, suffusing the medium with fast-growing roots to increase nutrient absorption and create the best conditions for plant production. One can sterilize and reuse rockwool, but most growers only use it once.
Other common hydroponic media are coir and gravel. Coir is a completely natural growing medium used in hydroponics. Made from the outer husk of the coconut, it is full of trichoderma bacteria that protect roots and stimulate root growth. It is easy to use because it has a perfect air-to-water ratio that prevents overwatering. It has a high cation exchange rate, so unused minerals are stored by it and released to the plant as needed. Gravel comes in different shapes and sizes, but it is washed before use. Water is circulated using electric pumps through the medium. It is inexpensive and clean to maintain. It doesn’t cause water-logging. But it is heavy and the gravel hydroponics system requires a regular supply of water to prevent plant roots from drying out.