Tuberous begonias are hardy to zone 10.
In all but the warmest hardiness planting zones, many summer and fall flowering bulbs, corms, rhizomes, and tubers will not survive a cold winter. Unlike hardy bulbs, which require a period of cold in order to bloom, these “tender bulbs” can’t handle the cold and need to be dug up, stored, and protected in colder climates. With a little practice, this can be done fairly easily and allows you to grow all sorts of plants that otherwise might not be winter hardy in your area.
Caladiums are tubers that can be treated as houseplants during the winter.
Tender bulbs that may need winter care include:
- Acidanthera (Gladiolus callianthus, corm): Hardy to zone 7
- Amaryllis (Hippeastrum, bulb): Hardy to zone 9 (Blooms indoors in winter)
- Caladium (Caladium sp., tuber): Hardy to zone 9
- Calla Lily (Calla sp., rhizome): Hardy to zone 7
- Canna Lily (Canna sp., rhizome): Hardy to zone 7
- Dahlia (Dahlia sp., tuberous root): Hardy to zone 8
- Elephant Ear (Alocasia sp., tuber): Hardy to zone 9
- Gladiolus (Gladiolus sp., corm): Hardy to zone 8
- Taro (Colocasia esculenta, tuber): Hardy to zone 8
- Tuberous Begonia(Begonia x tuberhybrida,tuberous root): Hardy zone 10
- Windflower (Anemone coronari, tuber): Hardy to zone 6
Cannas can be left in the ground in zones 7 and higher.
Digging and Storing Bulbs for the Winter
To overwinter your tender bulbs, follow these basic steps:
- As the weather cools, the foliage on your tender bulbs will begin to turn yellow. This often happens after a light frost but before a hard freeze. Now’s the time to dig them up, before they are damaged by freezing soil.
- Very gently dig your plants by loosing the soil all the way around the plant, several inches or more from the main stem. Use a fork or spade to carefully remove the plant from the ground, making sure not to damage the main bulb or underground food storage structure.
- Clean the bulbs by shaking off the soil and rinsing them. An easy way to rinse them is by laying them on a screen over your compost pile and using a gentle stream of water to wash the soil off the plants and onto the compost pile for recycling.
- Place the bulbs in a dry place out of the sun and wind and not subject to freezing temperatures for a day or two to dry.
- At this point, most bulbs and tubers are ready to store. However, corms such as gladiolus, calla, acidanthera, crocosmia, freesia, tigrida, and tritonia now need a “curing period” of about three more weeks. These corms cure best at warm temperatures up to 85° F and should not be left out in freezing temperatures, so try to coincide this with a spell of warm weather or cure them indoors.
- Sort the bulbs, removing any diseased or shriveled ones.
- Cut off the stems and foliage.
- Treat the bulbs, if you wish, with a fungicide and/or pesticide powder.
- Label your plants! In the spring it’s easy to forget what’s what, and it’s impossible to tell what colors you have. With larger roots, you can write the name and color directly on them with a permanent marker, or gently tie on a labeled tag. For smaller ones, you may want to use paper bags (not plastic!) as your storage container, so that you can label each bag.
- Fill ventilated containers with a loose storage medium such as peat moss, vermiculite, newspapers, or sawdust. Some gardeners slightly dampen the storage medium, but you don’t want it wet enough to invite mold.
- Layer the bulbs in the storage medium – don’t let them touch each other.
- Put the containers in a cool, dry place around 50° F. A dry, unheated basement, garage, or crawl space is a great spot as long as temperatures stay above freezing.
- Check on your bulbs several times throughout the winter. Throw away any shriveled ones, and remove any packing material that is rotten or moldy. Small rotten spots can be cut away with a sterile, sharp knife. If you see bulbs beginning to wrinkle or look shrunken, mist the packing material with a little water.
My Taro often loses its leaves when I bring it indoors, but it soon sprouts anew.
Overwintering Bulbs as Houseplants
If you’d like, you can simply plant your tender bulbs in pots, and bring them indoors as houseplants for the winter. Many tender bulbs will do just fine this way, although be aware that they’ll grow and bloom on their own schedule. Plants are very sensitive to the length of daylight, temperature, and humidity, and these factors are difficult to control.
Replanting in the Spring
In the spring, after all danger of frost has passed and the soil is nicely thawed and warm, you can replant your tender bulbs. You can also divide them at this time if you want. For a head start, pot your tender bulbs indoors in very early spring, and move them outdoors when appropriate.
Elephant ears grow larger each year, so they’re worth saving.