To store canna lilies during winter, wait until the foliage dies after a hard freeze, cut the foliage off 2 inches above ground level, use a shovel to dig the clump of rhizomes out of the ground, rinse the excess soil away, and allow the rhizomes to dry in a location with temperatures of 70 to 80 degrees Fahrenheit. After one week, transfer the rhizomes to a cool, dark location with relatively high humidity and good ventilation.
Dig the lilies up before the ground freezes, and cut the rest of the stems off the rhizomes before storing them. If desired, place the stems in the compost pile to produce extra rhizomes. To prevent damaging the rhizomes while digging them up, begin digging 1 foot away from the plant's stem.
Place the rhizomes in plastic bags or cardboard boxes after they dry. Store the boxes or bags in a location with temperatures ranging from 45 to 60 degrees Fahrenheit.
During winter, check the rhizomes occasionally, and discard any that are dead, discolored or diseased. After the danger of frost has passed in spring, divide the rhizomes so each piece has at least one leaf node, and plant the lilies 4 to 5 inches deep and 1 foot apart.