While gardeners in USDA hardiness Zones 8 and higher can grow tender bulbs, corms, rhizomes, and tubers year-round, northern gardeners must dig and store them indoors to over-winter and to save and re-plant next season. There are no absolute over-wintering rules, but in general:
- Keep them dry and above freezing temperatures
- Store in well-ventilated containers to reduce moisture build-up, rot, and fungus
- Fill containers with a dry packing material like peat moss, sawdust, or a vermiculite/perlite combination
- Inspect the storage container regularly for desiccation and mold
- Label bulbs, corms, rhizomes, and tubers by variety name and color
Following are specific tips for storing some commonly grown tender bulbs, corms, rhizomes, and tubers.
Alocasia (Elephant's Ear)
Treat alocasia as if it were a potted houseplant, feeding it lightly throughout the winter and watering often. When alocasia is grown in the ground, lift the plant before the first frost.and pot it up. Because plants tend to get larger as the tubers age, you might have to re-pot it again n early spring. Alocasia tubers can also be cleaned and stored in peat moss, in a cool, dry spot for the winter.
Anemone Coronari (Windflower)
Although these small bulbs are often sold in the fall, they are not hardy in Zones 5 and lower. To be safe, if you garden in a cold climate, follow the guidelines shown below for storing and over-wintering dahlias.
Allow a frost to kill the foliage of tuberous begonias, but do not allow the tubers to freeze. Dig and lift the tubers out of the ground and let them dry for one week, leaving about 5 inches of the foliage intact. Next, remove any excess soil and foliage and store the tubers in peat moss or sawdust at 50 degrees Fahrenheit. Re-pot the tubers in early spring and keep them warm, between 68 and 75 degrees Fahrenheit. When shoots appear, move the plant to a sunny spot and keep evenly moist, but not wet. Plant outdoors after all danger of frost has passed.
Dig and lift caladium bulbs before the first autumn frost and dry them in a warm location. Cut back the foliage after it dies. Caladium bulbs don't like to be stored in cold temperatures, so keep them at 50 to 60 degrees Fahrenheit. Pack the bulbs loosely in peat moss, then re-pot them in early spring, about 2 inches deep, knobby side up. Keep the soil moist and warm, between 75 and 80 degrees Fahrenheit. Move outdoors after the danger of frost is past.
Cannas are very easy to overwinter. Allow the frost to kill the canna foliage, but do not allow the rhizomes to freeze. Carefully lift the plants and cut off the dead tops, then hose off excess soil and allow the plant to dry. Wrap the rhizomes in newspaper and store them in paper bags or cardboard boxes at 45 to 50 degrees Fahrenheit. Cannas can be divided by hand—simply break them apart, ensuring there are at least three eyes per division. Re-pot in early spring or plant directly in the garden once the temperatures remain above 70 degrees Fahrenheit. Keep them well-watered.
Colocasia esculenta (Taro)
Like Alocasia, Colocasia can be brought indoors as a houseplant or dug and overwintered as a tuber. Store the dried tubers in peat moss and check them monthly, cutting away any soft spots that might develop. Allow the remaining healthy portion to dry before re-storing in peat. Colocasia can be repotted about eight weeks before the last expected spring frost. If dividing, be sure each tuber piece has roots. Allow the tubers to dry a few days before replanting them.
Dahlias can be over-wintered in the ground under a deep layer of mulch, but it is risky to do so in USDA hardiness Zones 7 and lower. To over-winter and store dahlias, allow the foliage to die back from the first autumn frost. Remove staking, cut back the stems to six inches, and leave the tubers in the ground for ten days. After ten days, dig and lift the tubers, remove excess garden soil, and dry them in a warm location for a few days. It's easiest to see the dahlia eyes, for division purposes, within a week after the foliage is cut back or killed by frost. Overwinter the tubers in a well-ventilated container filled with peat moss, sawdust, or vermiculite, Check them monthly for dehydration, misting lightly, if necessary. Don't let the tubers completely dry out. Dahlia tubers are usually directly planted in the spring garden after the danger of frost has passed and soil is at least 60 degrees Fahrenheit.
Galtonia Candicans (Summer Hyacinth)
Dig the bulbs anytime in the fall. Overwinter in peat moss, checking periodically to make sure they are not withered or rotting. When you are ready to replant in spring after all danger of frost has passed, separate the small offsets and plant both the main bulb and offsets directly in the ground.
Gloriosa Superba (Glory Lily)
Store in peat moss, checking the tubers monthly and cutting away any soft spots that might develop. Allow the remaining healthy portion to dry and callus before re-storing in peat moss. In general, use the same guidelines as dahlias. You can re-pot Glory lilies after only two months of storage or wait until early spring.