Mine have been fine in 1-gallon pots. My tallest one is 33" and packed with buds. I was worried because most people here said 2-gallon was the minimum.

But I found a lot of sources that said anything from 1-4 gallons was good so I stayed with them. I'm pretty satisfied with what I've got so far.

A buddy of mine grows 2 plants per 5-gallon bucket. He just sets them far enough apart that when the roots tangle it's far into the growing already so they don't kill each other.