Local nursery continually gives away plastic planters sized under a gallon, because they only return gallon size and up to those other areas growing the products wholesaled to the nursery (just ask one of the crew working the yard before pots are put in the dumpster). Being they're plastic, I've whacked many to better fit what height I wanted them to be. That was then, this is now. I like the methodology of a board screwed to bottom of tree and thrown in a collander (mostly pumice/lava by the way). If you're near enough I'll deliver most of my excess to you provided you got a bunch of collanders to trade.