| Rockwool, as someone has already said, is volcanic glass spun very thin and made into something that looks a bit like insulation. It absorbs water well and retains it, but also dries out quickly so it is good for preventing rotting roots. I use perlite on my own orchid (a phal) and it seems to be doing very well in just that. You have to make sure you water enough and feed regularly though as the perlite doesnt absorb much nutrition. |