CarolineScott said:--I saw some really coarse vermiculite which I will try to get as a bottom drainage aid. But it is expensive---but light so I could move ( drag) the bins if needed.
Hi Caroline,
A word of caution. You don't want to breath any dust or "fines" that might be associated with vermiculite or perlite. As a possible substitute for the coarse vermiculite, you might want to consider expanded polystyrene. It is sometimes sent as those molded packing pieces that items are shipped with, and sometimes as packing "peanuts" which are somewhat the shape of un-shelled peanuts.
You could probably use the shipping peanuts as is. You could break up the molded packing pieces into irregular broken shapes that you could use as lightweight styrofoam "rocks" or "gravel". Styrofoam is sometimes used as a cheap substitute for Perlite in "bargain" planting mixes. It appears as small white beads. In mixes, Perlite is much preferred to styrofoam, because Perlite does a better job of aerating a mix. But as a simple "volume filler", styrofoam might be safer than coarse vermiculite. And vermiculite can absorb water and become heavy, while styrofoam absorbs very little water and consequently stays lightweight.
In the past, some commercial vermiculite that was mined from some locations was contaminated with asbestos and that industrial product was considered a heath hazard. Today, horticultural grade vermiculite is probably safe, but I would avoid any non-horticultural grade of vermiculite. And use a mask to avoid breathing any kind of dust, just on general principles.
Just suggestions.
ZM
