The number of canna species has been reduced to 19, more or less, depending on which classification system that is being consulted. The original species are all from tropical or subtropical areas and have never been considered hardy in areas above zone 10. This idea may be changing The number of canna species has been reduced to 19, more or less, depending on which classification system that is being consulted. The original species are all from tropical or subtropical areas and have never been considered hardy in areas above zone 10. This idea may be changing with many of the cannas listed as hardy to zone 5 with a winter mulch. A number of less hardy ones are listed hardy to 14 degree F. Cannas have been so hybridized that they are almost always listed as cultivars rather than by species. They have been divided into 9 cultivar groups:
- 1 Foliage Group These are the strikingly colored leaf cannas that are grown primarily for their foliage.
- 2 Crozy Group Hybridized as early as 1862 by Crozy in France these have small to medium petals and resemble gladiolus
- 3 Italian Group Large petals and lips
- 4 Premier Group Large circular shaped cannas
- 5 Variegated Group All cannas with variegated leaves regardless of any other group they may belong to.
- 6 Conservatory Group Cultivars that have needs that are best met in a conservatory
- 7 Aquatic Group Cannas that thrive as marginal water plants
- 8 Miniature Group Plants that grow to approximately 15 inches with the flowers in scale.
- 9 Agriculture Group Cannas that have roots high in starch that are grown for human and animal food.
With the amount of cross breeding that has been done it is certainly possible that some cannas can be grown in temperate regions without lifting them for the winter. There is a water canna that was hybridized at Longwood Gardens from C. glauca that is hardy to zone 6 and apparently thrives in northern Indiana. There are a number of cannas that are listed as hardy to 0° including ‘Black Knight’ and ‘Lucifer’ that are readily available. Other hardy cultivars are listed here. A number of growers have been finding that the hardiness of plants is dependent, in part, on the area in which they are grown. Many plants that are hardy to zone 5 do not survive the winters in Western Pennsylvania because our heavy clay soil does not drain well enough to keep the roots from rotting in the winter. With cannas, and probably many other plants as well, a long hot growing season is needed. This allows the plant to build a high sugar content, which increases the rhizomes survival rate in lower temperatures. Starting the plants early or indoors can increase their hardiness. Cannas that are planted late in the season are probably not going to survive a winter. Some of the myth involving the lack of hardiness in cannas apparently originated in areas where plants were subjected to sudden cold snaps. The onset of sudden cold temperatures will often kill plants that haven’t had the chance to slow their growth naturally and initiate dormancy. Will cannas survive the winter in our area? There is certainly a possibility that they will dependent on the winter and the canna.