Substrate
Cultivating plants without soil, the accepted definition of hydroponics, continues to gain popularity within commercial horticulture, and as it does, more and more products are developed for it. More sophisticated lighting, easier to mix nutrients and simplified plant supports have all come onto the market within the past five years. But one of the most exciting developments in the world of hydroponics has been the refinement and popularization of alternative growing media.
There are probably hundreds of different kinds of growing media; basically, anything that a plant can grow in is considered a growing medium. Among the aggregates now available are rockwool/stonewool (the industry standard), oasis cubes, vermiculite, perlite, coconut fiber (coir), peat, composted bark, pea gravel, sand, expanded clay, lava rock, fiberglass insulation, sawdust, pumice, foam chips, polyurethane grow slabs and rice hulls. Each alternative has positives and negatives, and the choice between aggregates will depend on many variables, including the size and type of plants you wish to grow and the type of hydroponic system being used.