I grow a few in the ground continuously, but I have limited space, and I do it only to mature trees for a few years. The pot is whatever size and shape I want for the finished tree. They grow for two continuous growing seasons, but never for three. Ideally, I repot them, sink the pot and let it grow for two summers and repot in the following spring. The first summer gets good growth and some roots find their way out the drain holes. The second summer has explosive growth and most of the root growth is outside the pot, but the pot remains full of roots, too. It is easy to repot the following spring and all the roots outside the pot are the big kind you'd cut off anyway, so that works fine. The roots inside the pot have the right mix of sizes, so you cut off anchor roots in favor of feeder roots and what's left over are the right shape, mix and size for what I want. Repeat the cycle, ad infinitum. Never let them go the third year. All the growth is outside the pot and the pot is jammed with heavy roots. All the feeders will be outside the pot, so you have to undo that damage and that takes time, too. I don't believe in grow, chop, grow, chop. I monitor their growth just the same as if they were on a shelf. Failure to do so just means they return to type which always means apical dominance and empty bottoms. I don't have to grow that for myself, I can buy it at any nursery. Whenever I see references to quick growth, I shudder.