For me, the key would be whether it has been graded. Have the fines been sifted out? Because if they haven't, they will turn into a claylike mud once they get wet. Hand sifting is a pain, and it has to be perfectly dry (wear your N95!) Assuming it doesn't include fines, it can be used much like sand, although the grains tend to be more irregular so it has somewhat more resistance to erosion on a slope. Typically, once it is down to sand size, all the vesicles have been broken, so it is heavy and doesn't hold much water. If it is coarse, it will improve drainage while being otherwise inert. In a potting mix it can be used like a similarly graded sand (the pumice sand I use is a visually pleasant mix of black/white/grey/brown). I tend to use it instead of pumice/perlite due to my wind conditions. As a top dressing, I'd rake/mix it in...if I wanted to break up the clay, that would be a deep turning to get organic matter and sandlike material mixed in (excessively coarse pumice/perlite gets buried like this). Robert in cool San Francisco with lots of spots of color from the South African geophytes On Fri, Feb 5, 2021 at 1:14 AM Linda Press Wulf via pbs < pbs@lists.pacificbulbsociety.net> wrote: > I’ve ended up with three large bags of red volcanic sand. > > Would it be good to add it (and how sparingly?) to my bulb potting mix of > volcanic pumice and coir? How about spreading a half-inch all over my > large bed of South African plants to lighten the clay soil? And if so, can > I wait for it to integrate into the soil ( like a side dressing of compost) > without my digging it into the soil? > > I live in the Berkeley hills, Northern California, and the bed is on a > sunny slope. I spray water about once a fortnight in the dry summer. > > I would appreciate any advice. > Linda Press Wulf > _______________________________________________ > pbs mailing list > pbs@lists.pacificbulbsociety.net > http://lists.pacificbulbsociety.net/cgi-bin/… > Unsubscribe: <mailto:pbs-unsubscribe@lists.pacificbulbsociety.net> > _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net http://lists.pacificbulbsociety.net/cgi-bin/… Unsubscribe: <mailto:pbs-unsubscribe@lists.pacificbulbsociety.net>