My wife and I grow hundreds of callas in buckets and are able to leave them in them for two or three years before dividing them.In our spring, september as soon as we see the first shoot appearing above ground we give them all a good watering of nitrosol which contains giberallic acid which is the magic ingredient that triggers flowering. You probably wont have nitrosol in the U.S. but look for a fertilizer that does.You can buy the concentrated acid alone but the price here in N.Z.is enormous.Good luck as they are a beautiful flower.

When you dig up the bulbs look them over. Do they look like many small bulbs combined into one big one? If so, break them or cut them apart (gently!) and let them dry well before replanting.