I have not tried to grow one in a pot but the one I have in the ground has done great. Last summer (third year) it started blooming in mid summer and continued until frost. It even set 20 or so seed pods. It was in a 2 gallon pot when I planted it in the ground. The first couple of years it only had a scattering of blooms in the fall.
Patsy

Will probably need a much larger root space to develop fully and give desired display. Since wisterias (Genus Wisteria) can be pruned to remain small and still bloom heavily it might be possible to keep this one as a small specimen also, I don't know. But a 12 inch pot is probably still too small even using annual root and/or top pruning to control size.

I have had three Evergreen wisterias growing up trellises for the past 19 years...they are BEAUTIFUL!!!

I give them a good prune in the spring, and they come back in full glory with their deep purple blossoms from late June/July until frost. As the vines age, they do get thicker and I would say need more room. I have underplanted the vines with white star jasmine, so I don't really know how thick the wisteria root base is.

I hope you love them as much as I have over the years!!!

~ Mary Jane