Although hydroponic gardeners use no soil, a plant’s roots must be supported by a ‘growing medium’. The best media are pH neutral, provide sufficient support for the plants, retain moisture, and allow space for the exchange of air. Heydite, clay pellets, Perlite, vermiculite, and Rockwool are the most popular growing media.
The type of medium used depends on the size and type of plants you wish to grow, and the type of hydroponic system being used.
For continuous drip systems, Haydite (a porous shale) or Hydrocorn (clay pellets) are best. The pebbles provide enough drainage and air space to take advantage of continuous feeding, and also provide good anchorage for larger plants, are easy to clean, and can be re-used indefinitely.
Rockwool is another popular medium, and it can be used with continuous drip or flood and drain systems. It provides roots with a good balance of water/oxygen. Different sized cubes are used at different stages of a plant’s life. Rockwool. Although it is possible to sterilize and re-use Rockwool, usually it is used only once.
Made from volcanic rock, Perlite’s small, white pellets are often used as a soil additive. Perlite can be used alone as a growing medium for smaller plants, but it does not provide enough anchorage for large plants.
Vermiculite is used the same way as Perlite, and the two are sometimes combined. Vermiculite is made from heat-expanded mica and has a flaky, shiny appearance.
Some hydroponic systems do not require any growing medium at all. Various methods are used to support the plants while the roots are directly fed nutrient solution.