when it comes to autoflowering plants,I have found they need a deep container.I have best results using breadbags.I have tried everything from small containers up to 5 gallon paint buckets and for me at least,it seems they need a deep container as soon as they break ground. have been playing w/ a LR2/NYCdiesel cross & the only way to get them to grow over a foot high is to get them into 12 inches of soil asap.waiting and stepping up containers as they grow didnt help & width of the pot didnt seem to mater.my guess is they throw down a deep taproot & how far it gets determines how tall the plant will grow.
when it comes to regular plants,I just stopped by my mentors place last night & he had a batch ready start flowering.they were in 1/2 gallon pots & we switched them to 1 gallon.all were between 2-3 feet and had been trimmed like a lolipop.he has grown for about 30 yrs & produces the best bud I have ever seen. all organic in soil in 1 gallon pots.it beats the best shit coming out of California's med shops hands down.