In the garden, plant canna rhizomes horizontally 5 inches deep, and cover them with a thick layer of mulch. Leave about 2 feet of space around the rhizomes. These plants don't like to be crowded, and if other plants encroach they might refuse to bloom. After the first frost of the fall, cut the canna back to the ground. In colder climates, carefully dig up the rhizome clumps and store them for the winter in peat or vermiculite in a spot that doesn't fall below 40 degrees Fahrenheit. (You can simply bring container plants indoors in their pots.) Spray the rhizomes with water infrequently to prevent them from drying out, but don't allow them to sit in a consistently damp medium. Canna leaves have a waxy coating that helps the plant resist fungal diseases.