While gardeners in zones 8 and above can grow tender bulbs, corms, rhizomes, and tubers year-round, northern gardeners will need to dig and store these plants to overwinter them. There are no absolute rules for overwintering the tender plants but in general:
- Keep them dry and above freezing temperatures.
- Don't store in airtight containers that could cause moisture build-up and rot or fungus.
- Check regularly for desiccation and mold.
- Remember to label by type and color.
Below are more specifics for some commonly grown tender bulbs, corms, rhizomes, and tubers.
Easiest to simply treat as potted houseplants. Feed lightly throughout winter and water often. If ground grown, lift and pot before frost. Alocasia tubers can also be cleaned and stored in peat moss, in a cool, dry spot. Plants tend to get larger as the tubers age. Re-pot in early spring.
Anemone Coronari (Windflower)
Although these small bulbs are often sold in the fall, they are not hardy in Zones 5 and lower. Be safe and follow guidelines given below for storing dahlias.
Allow a frost to kill the tops but do not allow the tubers to freeze. Lift and let tubers dry for one week, with about 5 inches of the foliage still intact. Remove excess soil and foliage and store in peat moss or sawdust at 50 degrees F. Re-pot in early spring and keep warm, 68 - 75 degrees F. Move to a sunny spot when shoots appear. Keep evenly moist, but not wet. Plant outside after all danger of frost.
Lift caladium plants before a frost and allow them to dry in a warm spot. Cut back the foliage after it dies. Caladium bulbs don't like to be stored in cold temperatures. Keep them at 50 - 60 degrees F. Pack the bulbs loosely in peat moss. Re-pot in early spring, about 2 inches deep, knobby side up. Keep the soil moist and warm - 75 - 80 degrees F. Move outdoors after all danger of frost.
Allow the frost to kill the tops but do not allow the rhizomes to freeze. Carefully lift the plants and cut off the dead tops. Hose off excess soil and allow it to dry. The rhizomes can be wrapped in newspaper and stored in paper bags or cardboard boxes, at 45 to 50 degrees F. They are very easy to overwinter. Cannas can be divided by hand. Break apart, ensuring there are at least 3 eyes per division. Re-pot in early spring or plant directly in the garden once the temperatures remain above 70 degrees F. Keep well watered.
Like Alocasia, Colocasia can be brought indoors as a houseplant or dug and overwintered as a tuber. Store the dried tubers in peat moss. Check the tubers monthly and cut away any soft spots that may develop. Allow the remaining healthy portion to dry before restoring in peat. Colocasia can be repotted about 8 weeks before the last expected spring frost. If dividing, be sure each tuber piece has some roots. Allow the tubers to dry a few days before replanting them.
Dahlias can be over-wintered in the ground with sufficient mulch, but it is risky. To store dahlias, they must be dug before a hard freeze, but their tops may be allowed to die back from a light frost. It's easiest to see the dahlia eyes, for division purposes, within a week after the tops are cut or killed back. These tubers don't like to get completely dried out. Overwinter in peat moss and check monthly for dehydration. Mist lightly, if necessary. Dahlia tubers are usually directly planted in the garden, once temperatures warm.
Galtonia Candicans (Summer Hyacinth)
Dig bulbs anytime in the fall. Overwinter in peat moss and check periodically to make sure they are not withered or rotting. When you are ready to replant, after all danger of frost has passed, separated the small offsets and plant both the main bulb and offsets directly in the ground.
Gloriosa Superba (Glory Lily)
Store in peat moss. Check the tubers monthly and cut away any soft spots that may develop. Allow the remaining healthy portion to dry and callus before restoring in peat. In general, use the same guidelines as dahlias. You can re-pot Glory lilies after only 2 months of storage or hold until early spring.