Stefan Buczacki solves your plot problems
Andrew Peterson, by email
Stefan says: Of course, like all other subjects, gardening must advance, and many of the plants, techniques and materials that we take for granted today would have been alien to our parents and grandparents. Rockwool is one of these, and if you look around commercial greenhouses where tomatoes, lettuces and orchids are being grown, you will see rockwool by the ton. So, what is it? Rockwool is a type of rock, or at least, a type of mineral: aluminium silicate to be precise, although there is some calcium and magnesium present, too. Someone discovered that if this raw mineral is heated to 1,000C (1,832F) and then cooled, it solidifies in the form of fibres, and produces a coarse, woollike material, which has a high water-holding capacity. Being moisture retentive, it’s used as a compost or growing medium in its own right. But as it has no nutrient content of which plants can make use, those grown in rockwool are wholly dependent on being supplied with a liquid fertiliser.
The advantages of rockwool, especially to a commercial grower, are that it’s sterile, uniform, fairly easy to handle and, having no nutrient value, affords the opportunity for total and precise control of the plants’ fertiliser supply. Nonetheless, while I would be pleased to see gardeners and amateur orchid growers use the material, I would be wary of throwing all of your eggs into this basket until you’re certain it satisfies all your requirements.
For unless you have some facility for cleaning and re-using rockwool and decide to use it on a large scale, you could well find that you’ve a serious disposal problem on your hands, as it won’t rot down in a compost heap in the way that traditional composts do.