On 5 Oct 2009, at 18:02, Leo A. Martin wrote: > 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. Change that "is" to "may be". If you feel you must use insulation grade perlite in spite of these warnings, you can mitigate the risk by adding lime to the mix as calcium fluoride and magnesium fluoride are very insoluble and thus the presence of Ca++ and Mg++ ions in the soil will tend to soak up any F- released by the perlite. -- Rodger Whitlock Victoria, British Columbia, Canada Maritime Zone 8, a cool Mediterranean climate on beautiful Vancouver Island http://maps.google.ca/maps/…