If it is starting to break dormancy, I would start with a pot no larger than two inches in diameter than the tuber. Let it grow and then decide on the size of the pot. It may not get as large as those catalog photos lead you to expect. The environment in which you grow determines everything.

woebegonia (cute!)...Thanks for your response...I don't understand what you mean by "break dormancy"...there is a whitish "stem" type of thing coming out of the indented side of the bulb...I purchased the bulb from McClure and Zimmerman...Georgeanne

That is the stem coming from the indented side, the round side produces roots. When the see the stem starting (some people call them 'eyes') you can place the tuber on damp soil and you should see a root or two coming along there soon. Don't cover the tuber, thoough, for quite a time, you want to see definite growing progress first.