Depends on cultivar, my Papillio roots do fill 14 inch pot for others I use 10 inch pot.

tends to depend on the size of the bulb. I usually only repot them when the roots start pushing the bulb up out of the pot. ive never really seen a difference between hippeastrums in pots or the ground, but the pot protects them from burrowing insects that can be a real problem to control. that and theyre easier to move in pots. im in an area that gets frost, so I have to bring them in. you really don't want to damage the roots on these, they take a long time to regrow, so the easier to move without digging them up, the better

considering how root bound my bulbs got this time around - I put them in bigger pots this round to see how big the roots get. they are all pretty happy right now and i am waiting on several seed pods. with my seedlings - i might run a couple experiments with pot depth...

With very big pots I do not experimented but noticed - the more and deeper the pot, the seedlings grow faster.