Tom wrote, 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. I live where horticultural pumice is readily available. In general we can get two grades, washed and unwashed. Most nurseries use the washed product and mix it with composted fine bark, which is also very cheap and lightweight. Because I grow summer-dormant bulbs, I avoid using bark in the mix because I think it hosts microorganisms that also attack the bulbs, or at least their tunics. The washed product, which has a fairly large average particle size (I think about 4 to 5 mm), will "float" to the top if mixed with heavier components, such as the coarse sand I also use, so I prefer the unwashed product, which has particles from about 7 mm down to dust. I think the fines in it make the significant nutrients in pumice more available to the plants. Not everyone agrees that having fines of any kind in a potting mix is desirable, however; you do have to manage your watering very carefully so as not to waterlog the mix. Having maintained many of my bulbs in this mix for more than 15 years, I like it anyway. I don't know if the unwashed (unscreened) product is available anywhere outside the immediate area where pumice is quarried. This is white to gray pumice, by the way; the term "pumice" is also applied in the trade to a dark red volcanic rock which, I am told, is more properly called "scoria." The red pumice, or scoria, is mostly used in large particle sizes (3-4 cm) as mulch. Loren Russell has informed us that it contains very significant nutrient levels, and he has gone to rock yards and scooped up the fine detritus in the bottom of the scoria bin to use in growing alpines. I use the smallest size of scoria that can be bought here, about 1 cm diameter, as a top-dressing for some bulbs. Our NARGS chapter in Portland recently heard a talk by Truls Jensen of Wild Ginger Farm nursery called "Fresh air," which featured his techniques for increasing air space in container soils in order to grow xeric plants successfully. Wild Ginger, a mail-order nursery, has a very interesting plant list: WildGingerFarm.com Jane McGary Northwestern Oregon, USA