| Sounds like the pots are too small, they ran out of room. Canna produce large rhizomes that fill a gallon-sized nursery pot very quickly. Zone 7 and up you can plant in the ground and they will reproduce like crazy. Mulching will help protect them from winter cold. When they are crowded the rhizomes will grow ontop of previous growth. Zone 6 and lower where the ground freezes you much dig and store for the winter. Happy Gardening!
Peggy | 
