In mild winter climates, winter rains rot the tubers more often than cold kills them. If the soil rarely freezes down to the 5-inch level where you plant the rhizomes, you can use this no-dig method of canna storage.
1. Plant cannas at the top of a mound or in a raised bed for good drainage.
2. Cut back top growth all the way to the ground in the fall.
3. Cover the mound or bed with a tarp or heavy plastic to keep out rain and snow.
4. Mulch with a few inches of pine needles, bark, or straw to add insulation and keep the covering in place.
5. In late spring, remove mulch and tarp so cannas can emerge from dormancy.