Another option is to check around for "sponge rock". This is large sized perlite that some orchid growers use in their growing media. Eugene Zielinski Augusta, GA USA > [Original Message] > To: Pacific Bulb Society <pbs@lists.ibiblio.org> > Date: 10/6/2009 8:26:18 PM > Subject: Re: [pbs] Well-drained growing media (was Oh No! A Boophonedisaster!) > > 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 > _______________________________________________ > pbs mailing list > pbs@lists.ibiblio.org > http://pacificbulbsociety.org/list.php > http://pacificbulbsociety.org/pbswiki/