I don't use many band pots (the term for the kind of open-based pots being discussed here), but when I do, I crumble some oak leaves coarsely to put in the bottom, since I don't have screen handy to cut up in little squares as done by growers who use band pots a lot. I don't think this creates a perched water table in the mix I use, which does not contain Perlite, and there are always plenty of oak leaves around here (the neighborhood is known as Oak Grove and was originally a Quercus garryana savanna plant community, with many of the old oaks still around). Any slow-rotting leaves would probably do. Band pots come in quite a range of sizes, but they are made of rather brittle plastic. Growers who need large, sturdy pots with a great deal of air circulation might be interested in a kind of larger pot used by field nurseries for young trees, which are heavy black plastic with large openings all over; they sink these in the soil and root prune around them to lift and deliver the trees. I have a few left over from tree planting and will use them if I need to grow a big, rather tender epiphytic plant that has to be moved indoors in winter. Probably the suppliers mentioned here earlier sell these also. Jane McGary Portland, Oregon, USA