> On a related point, I wonder if anyone with experience of using it > would advise me which grade or particle size of pumice to use for > horticultural applications. I've never used it but am keen to experiment > with it after reading the recent correspondence on Boophone and other SA > Amaryllidaceae. So much of this depends on your climate and the plants you are trying to grow. People in wetter and more humid areas generally succeed with more open mixes of larger particle size. People in drier, more arid areas look for smaller particles. Bulb seedlings usually need a more water-retentive mix. But the general idea is to use a combination of soil mix plus container that almost dries in the same time frame as your preferred watering interval. For example, Phoenix has very low winter humidity and warm days unless it's raining--often under 10% for weeks on end. I use non-porous containers twice as deep as wide and a soil mix of sand mixed with native granite soil for my winter-growing bulbs. I suspect in Oregon with this mix and containers my seedlings would rot quickly, but my problem in Phoenix is keeping seedlings damp enough. Perlite works well under many circumstances but horticultural perlite available here is of quite small particle size and it stays wet a very long time. With watering, perlite, if mixed with anything else, soon floats out of the heavier stuff and forms a zone of pure perlite at the top of the container, with the heavier stuff below this. Then the perlite blows out of the pot in the wind, or it is splashed out with watering. I have wanted to try some of the larger-particle perlite, often used for insulation, but I have been warned much of this is very high in fluoride and toxic to plants. I don't know where to find it in any event. I would definitely encourage people to wash the pumice to remove the powder unless you wish a more water-retentive mix. And remember to wear a mask when working with pumice or perlite; the dust can cause lung disease. That goes for pretty much anything that is dusty--peat moss, coir, scoria, etc. etc. etc. Leo Martin Phoenix Arizona USA