“I just want to say one word to you. Just one word. ... Are you listening? ... Plastics.” ― Mr. McGuire, The Graduate
One of the problems when you go collecting yamadori, especially at this time of year, is finding a pot large enough to let it recover in before you can start training your new tree. Sometimes, you need to let them recover for a couple of years, and when you start out, they have huge root balls that you want to leave intact until the tree has had time to recover.
My favorite choices: shipping crates (when I can get them for free) and these things - plastic party tubs.
For eight bucks, plus the trouble of drilling a few drainage holes, you can fit almost any root ball you might dig out. If you don't drill them out, they are also great for mixing soils, soaking trees overnight after collection, carrying lots of little pots with seedlings, and all sorts of other tasks. I have about 10 of them, and I use them all the time.