Originally used for insulation purposes only when it was referred to as mineral insulation, rockwool has found its perfect place in hydroponic gardening. It is currently the leading grow medium the world over – thanks to its amazing properties that allows it hold a lot of air and retain a high amount of water at any given time. Its use has changed the way that hydroponic gardening is carried out where the plant root system is supported by a growing media instead of being bathed directly in the nutrient solution.
Rockwool was first used for gardening in Denmark and has since gained popularity all over the world because of its versatility. It has been used for a long for insulation, but it was discovered in the early 1960s that if certain modifications were made to its manufacturing process, rockwool would promote plant growth. Basically, it is made by melting a mixture of rocks mostly basaltic and dolomite rock at very high temperatures and spinning the melt into fibres. The fibres are then compressed and cured into large slabs, where its density is adjusted by adjusting the amount of pressure on it.
All rockwools are not the same and one has to make his/her choices right for the best gardening results. Rockwools produced from pure basaltic rock, for instance, are considered the best since they have a good mineral balance and are non-reactive. Rockwools made from slag left over from smelting operations, on the other hand, are not the best since they contain a high level of metal ions which are reactive with the nutrient solution.
The most striking feature about rockwool is its ability to retain a high amount of water and hold as much air as 18%. Both of these elements are essential for plant growth. It is also clean and convenient. However, the major problem is its disposal. It is very hard to dispose since it is not easily decomposed and its dust and fibres pose a great health risk.