Canna plants have large leaves and loose spikes of flowers which add tropical flavor to the summer garden. Giant canna varieties grow to an average height of 6-8 feet. Cannas are not hardy, but they produce tubers, like dahlias and tuberous begonias. Dig up rooted tuber just before frost and trim excess foliage from root. Store in a bushel of sand in a cool, dark area (frost free) until April. Re-pot tubers in gallon containers for July blooms.