On Wed, Oct 24, 2012 at 9:50 PM, Hannon <othonna@gmail.com> wrote: > The pumice available here, mined in eastern CA and in NV, provides good > surfaces for roots and water to adhere to but water and roots do not pass > through the particles-- the "holes" in the pumice are locked inside the > individual pieces. This material has been a staple for cactus industry for > years, but it should be noted that most wholesale production of cacti & > succulent utilizes only a mix of organics like SuperSoil and fine perlite. > There is often a sharp difference between successful approaches to nursery > production versus methods of maintaining plants longer term by hobbyists. > > Since it is a natural product, what is sold as the same item (pumice) can > vary from very clean and sharp-edged particles to soft-edged rounded > particles with more dust-like fines included. I agree with Jane that the > fines are helpful to the roots, in part by coating them and protecting them > with a 'powder coating', especially when plants are dormant. Fines in > general, especially organic ones, help with cation exchange (places where > nutrients can be stored in the soil). It is unfortunate that pumice is so > difficult or expensive for growers to obtain in practical units regardless > of where they live. > > Scoria sounds like what is also known as cinder. This is volcanic material > that is crushed in huge quantities to make cinder blocks and this seems to > be its nearly exclusive use. A fine grade of cinder (black or red) with > pieces 1-2mm is very clean and sharp and one of the best materials I have > found to start seedlings of cacti, bulbs, etc. Again, with horticultural > demand so low it is no wonder it is difficult to find a source for it. > > Dylan Hannon > _______________________________________________ > pbs mailing list > pbs@lists.ibiblio.org > http://pacificbulbsociety.org/list.php > http://pacificbulbsociety.org/pbswiki/ >