The silty sediment can be quite helpful in clinging to roots and protecting them from drying in an otherwise open "clean" mix. A lot of these fines wash through after the first few waterings. Dylan On 12 July 2012 12:05, Gastil <marygastil@yahoo.com> wrote: > Having heard good things about pumice on this list, > I went to our OSH and purchased a small bag of Black Gold brand pumice. > It was about 10 times heavier than I expected pumice to be, but they > assured me that was just because it was wet. > At home, I noticed it had a lot of dust, which I did not think I wanted in > my growing medium > (not having read the note from Jane yet about the dust containing useful > minerals). > When I washed the pumice, I noticed it sank. I expected pumice to float. > The pumice in Baja California floats and resembles styrofoam. > I wrote to Black Gold and they replied > > "The Black Gold Pumice that you bought comes from a source in central > Oregon, > the same source we have used for a long time. Chances are that you will > get the > same type of pumice in California, Oregon and Washington, if you buy Black > Gold. > This is a denser pumice, but should not affect the porosity you are > seeking. > The dust comes from the pumice rubbing against itself in the packaging as > it is moved around." > > I also noticed when I washed it that I could sieve out the sizes to get > pebbles for topping and > grit to sand size for growing medium and could wash away the silt-sized > sediment. > > - Gastil > _______________________________________________ > pbs mailing list > pbs@lists.ibiblio.org > http://pacificbulbsociety.org/list.php > http://pacificbulbsociety.org/pbswiki/ > -- "*Reason is itself a matter of faith. It is an act of faith to assert that our thoughts have any relation to reality at all.*" ~ Gilbert K. Chesterton