On the subject of perlite, I use it in my larger pots so they are not so heavy when I move them. As that which is near the surface has a tendancy to float up I top the upper three or four inches with the same mix as in the rest of the pot only without the perlite. I have been mixing drystall with sharp sand and compost in varying proportions and have not encountered an clumping issues. Randy, Monterey Bay Region, CA