The deepest ones I’ve got experience with are about 14" deep, with a top of 2" square tapering to a 1.5" square at the bottom - theoretically, you could get away with growing in those for up to a full season but you’ll have to worry about encircling roots and the trees may experience difficulty during transplanting if something isn’t done to free them from that shape. Wider grow bags would definitely give you a buffer in that they’ll have more room for the lateral roots, but many of the ones I’ve tried wick moisture from the substrate so you may need to devote additional time to watering.

Something we’ve had good success with is the use of air prune boxes (apologies for the self plug but it’s something to which I have quick access), which do limit the length of the taproots during the time in the box but substantially increase the amount of fibrous roots the trees will grow. Once transplanted, the taproots will resume normal growth behavior. Here’s an introductory article about them from someone other than me writing for Mother Earth News. We grow a number of woody plants in air prune boxes for a full growing season, at which point we remove them and either plant or ship them during the fall and early winter. I can’t recommend them enough, but it’s important that you choose the method that will work best for your circumstances, time, and means.