Canna lilies have tender tubers. In warm climates where winter temperatures rarely drop below 40 degrees F, mulching the flower bed would be sufficient to protect them frost and freezing. In most places, like here in Cincinnati where fall and winter temperatures will drop below freezing, canna lilies will need special care to survive cold temperatures. You may also need to store your Dahlias, Gladiolus and other tender weather bulbs and tubers. This technique works for every bulb I have ever stored over the cold winter months.
Before you dig up your tubers you need to think of where you will store them. You can use a box, large bucket or heavy plastic garbage bag and fill it with damp sand, sphagnum peat moss, coarse sawdust or vermiculite particles. I prefer to keep mine in 4′ frames with screen material stapled to the bottom. I like this because it is easy to spray the bulbs and tubers to remove the remaining dirt and it allows air to circulate during storage.
Allow the first fall frost to blacken the foliage of the canna lilies.
You can dig them up as long as the soil is workable and snow or frost hasn’t crusted the soil surface. Start digging 6 inches away from the base of the plant. Use the shovel to loosen the roots. I lightly tap the tuber on the ground to remove any loose soil.