I have two beautiful pots of canna tropicanna. I overwintered them last year and they came back with a vengence this year so I have way too many in each pot.

Although the foliage is great they have not bloomed yet, I'm thinking because they are so overcrowded. Anyway I need some guidance on how to get them divided. Do I divide and re-pot in the fall when bringing them in for the winter? or do I leave them in the pot and wait til spring? I've never divided them and don't even know how to begin. Advice would be greatly appreciated.