Many summer-blooming tender perennials are great additions to the garden but are not winter hardy in Iowa. These tender perennials must be dug up in the fall and stored indoors over winter. This is possible because these plants grow from bulbs or other geophytes like corms or tubers.
The Basic Steps
In general, prune tender perennials back just before or just after the foliage is killed by frost in the fall. Carefully pull the bulbs (or tuber, rhizome, corm, etc.) out of the ground and remove any excess soil. Allow bulbs to dry and then store in a cool, dark, and dry location. Temperatures must not get below freezing. Cardboard boxes, plastic crates, paper bags, mesh bags, or containers of peat moss, newspaper, sand, or vermiculite are all options for winter storage. Bulbs must be allowed to stay dry enough to remain dormant and free from moisture-loving mold or fungus, but damp enough to not dry out and shrivel up.
Check on bulbs periodically throughout the winter. Remove any rotting, soft, or dried-out bulbs that may develop. If conditions are too dry, very lightly moisten the material they are stored in. Be careful to not over water as it will lead to rot, mold, and fungal growth.
The storage organs of most tender perennials multiply quite quickly in the garden. Leave them intact until spring as any injury incurred prior to storage will increase the chances for rot to occur. In the spring cut the rhizomes and tubers apart making sure at least one or two dormant buds are present on each section. Share the extras with relatives, neighbors, and friends.
Often the most difficult part of storing tender perennials for home gardeners is finding a location with the correct temperature. Often an unheated basement or extra bedroom in which to store the tender perennials adequately is not available. Normal interior temperatures are too warm. Most garages, even though attached, will be too cold for survival. If this is your situation, it would be best to grow these plants as annuals instead of perennials.
Specific Recommendations for Common Tender Perennials
Canna | Caladium | Elephant's Ear | Dahlia | Gladiolus | Calla Lily | Banana | Tuberous Begonia
The storage requirements for several widely grown tender perennials are provided below.
Canna (Canna spp.)
Cut the plants back to within 4 to 6 inches of the ground a few days after a hard, killing frost. Then carefully dig up the canna clumps with a spade or fork. Leave a small amount of soil around the cannas. Allow them to dry for one to two days. Afterward, place the canna rhizomes in large boxes, crates, or in mesh bags. Store in a cool (40 to 50°F), dry location.
Caladium (Caladium bicolor)
Carefully dig up the caladiums when the foliage droops and begins to yellow with the onset of cool fall temperatures or wait until after the first hard frost. Gently shake the soil from the plants. Then place the caladiums in a warm, dry location for 1 or 2 weeks to cure. Afterward, cut off the dry foliage and bury the tubers in dry peat moss or vermiculite. Store the tubers in a cool (60 to 65°F), dry location.
Elephant’s Ear (Colocasia, Alocasia, and Xanthosoma)
Dig up the plants after the first fall frost. Cut off the foliage. Dry the corms or tubers in a warm, dry location for 1 or 2 weeks. After drying, bury the corms or tubers in peat moss or wood shavings and store them in an area with a temperature of 55 to 60°F. This storage temperature is a little warmer than most tender perennials.
Some species and varieties do not form underground structures like corms or tubers. Overwinter these plants as houseplants in a warm, bright location. Bring them indoors before nighttime temperatures drop below 45°F
Dahlia (Dahlia spp.)
Several days after a hard frost, cut the plants back to within 2 to 4 inches of the ground. Carefully dig up the tuberous roots with a spade or shovel. Gently shake off the soil and then cut the stems back to the crown. Wash the tuberous roots to remove any remaining soil. Allow the tuberous roots to dry to the touch (usually about 1 day). When dry, place the dahlia clumps upside down in boxes or other containers and cover them with vermiculite, peat moss, or wood shavings. Store the dahlias in a cool (40 to 50°F), dry location.
Gladiolus (Gladiolus spp.)
Carefully dig up the plants with a spade in late summer/early fall. Gently shake off the soil from the bulb-like corms. Then cut off the foliage 1 to 2 inches above the corms. Dry the corms for 2 to 3 weeks in a warm, dry, well-ventilated location. When thoroughly dry, remove and discard the old dried-up mother corms located at the base of the new corms. Remove the tiny corms (cormels) found around the base of the new corms. Save the small corms for propagation purposes or discard them. Place the corms in mesh bags or old nylon stockings and hang in a cool, dry, well-ventilated location. Storage temperatures should be 35 to 45°F.
Calla Lily (Zantedeschia spp.)
After a killing frost, cut off the foliage 1 to 2 inches above the soil surface. Carefully dig up the rhizomes. Do not cut or injure the rhizomes. Dry the rhizomes in a warm, dry location for 1 or 2 weeks. After drying, bury the rhizomes in peat moss or vermiculite and store them in a cool (50 to 60°F), dry location.
Banana (Musa spp.) & Abyssinian Banana (Ensete spp.)
Dig the entire plant up just before the first frost. Do not cut leaves or stems back. Leave some soil around the roots and wrap the root ball in a plastic bag. Store the uprooted plant in a cool, dark location (45 to 50°F). Allow the leaves and stems to dry down naturally. Remove the dry, brown stem before replanting outdoors in spring after the danger of frost has passed.
Tuberous Begonia (Begonia xtuberhybrida)
Carefully dig up the tuberous begonias within a few days of a killing frost. Leave a small amount of soil around each tuber. Cut off the stems about 1 inch above the tubers. Place the tubers in a cool, dry area to cure for 2 to 3 weeks. After curing, shake off the remaining soil, and then bury the tubers in dry peat moss, vermiculite, or sawdust. Store the tubers in an area with a temperature of 40 to 50°F.
More information about overwintering tender perennials can be found in this publication: Growing and Over-wintering Tender Perennials