How much winter care your canna lilies (Canna spp.) need depends on your hardiness zone. Cannas growing in U.S. Department of Agriculture plant hardiness zones 7 through 10 can remain in the ground over the winter. If you live in USDA zone 6 or lower, you will need to lift the canna rhizomes and store them.
If you're growing potted cannas in a cold-winter climate, simply move the pots indoors after the first fall frost kills their foliage back to the soil. Store them in a cool, dry area, such as an enclosed porch or unheated garage, where the temperature remains between 40 and 55 degrees Fahrenheit, until spring.
Lifting Canna Bulbs
To lift the canna rhizomes for winter storage, wait until frost blackens their leaves.
Things You'll Need
Sharp, clean pruning shears
Two clean rags
Dry peat moss
Cut the blackened leaves back to 3 or 4 inches above the soil with clean, sharp pruning shears disinfected between cuts with a clean rag moistened in rubbing alcohol. Discard the leaves. You can add them to a compost pile.
Dig in a circle around each clump of cannas, 6 to 8 inches from its perimeter. As you dig, carefully angle the spade down and in until it's beneath the rhizomes. Work it back an forth to loosen the entire clump.
Lift the clump, shake it to remove excess soil and wipe the individual rhizomes with a second clean rag.
Examine the rhizomes for spade wounds. If you find any, set the clump in a cool dry spot for a few days while the wounds form calluses.
Divide each clump into smaller sections, each with three to five raised growing points, or eyes.
Wrap the divisions in clean, dry peat moss and store them in a dark, cool dry spot with temperatures between 40 and 55 F until spring.
Overwintering In-ground Cannas
In USDA zones 7 through 8, cannas left in the ground for the winter benefit from a layer of soil-insulating organic mulch applied in fall. Well-aged compost is a good choice. Spread a 3- to 4-inch layer evenly over the soil around the plants. The compost releases nutrients and improves soil drainage.
A 3- to 4-inch layer equals 90 to 120 pounds of compost for each 10 square feet of soil.