Tractor Supply feed pans have become my favorite for large BC. I usually drill 3 holes around the bottom edge and make wooden plugs to hold water in for a month at a time. I then let them drain for a week and fill them back up.
Here is one that's already pretty good size ...... almost 10" across the base. This is 90% through only it's second season from a stump. The apex is just about finished. Oh, and almost pure organic soil is what we've found to work best in the growing stage.
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