Overview
Plants commonly referred to as tender bulbs include a range of species which develop and grow from fleshy storage structures (true bulbs, corms, rhizomes, tubers, and roots) which do not survive Wisconsin’s cold winters outdoors. These include caladium, calla lily, canna, dahlia, elephant ear, gladiolus, tuberous begonias, and others. Even though not all are technically true bulbs, the term “bulb” is commonly used for this group, for convenience. As they are not winter-hardy, these plants need special treatment to save for the next growing season. Many of these bulbs are expensive, yet easy to keep, so it can be worth the trouble to dig and store the underground portions of these plants for replanting the next season.
This article provides some general guidelines and safeguards to make the process of overwintering tender bulbs more successful. The two most important factors are to keep the bulbs dry and cool and protect them from freezing temperatures before and during storage.
Digging Tender Bulbs
Dig up tender bulbs after the foliage dries up or just after the first frost. A light to moderate frost will not penetrate to the depth of the bulb but will kill top growth. If the foliage is killed by frost, dig the bulb within a few days to ensure rot-causing organisms do not enter the bulb through the damaged above ground parts. There are a few exceptions to this method. For instance, Peruvian daffodil (Hymenocallis) needs to be dug before frost damages plants.
Dig carefully to avoid damaging underground structures. A digging fork is less likely than a shovel to cause injury. Loosen the roots gently by digging several inches back from the base of the plant on all sides before lifting the clump. Avoid cutting or bruising the bulbs, and take special care not to rub off the skin of dahlia tubers. Pathogens can readily enter through injured areas to cause rot in storage.
Cleaning Tender Bulbs
Shake off excess soil as bulbs are dug and cut off the stems. Gently wash off the remaining soil with a hose. Placing the bulbs on a wire mesh screen make washing easier. Gladiolus corms are best left unwashed; the remaining soil can be removed after drying. Discard any bulbs that are obviously damaged.
Wait until spring to divide dug bulbs if they have multiplied, as injury increases the chance of rot in storage.
Curing Tender Bulbs
Most bulbs need a period of curing, or drying, before storage. For most species curing takes 1 to 3 days, depending on temperature. A few plants, such as gladiolus and calla, need a curing period of about three weeks. Keep the bulbs out of direct sunlight in a dry, well-ventilated area where the temperature is 60 to 70 °F when curing. After curing gladiolus, remove any old, shriveled corms at the base of the mother corm.
Storing Tender Bulbs
Inspect the bulbs for signs of insects and diseases before storage. You may choose to dust the bulbs with a fungicide mixture labeled for the specific species as a preventative. This is most helpful when there has been a previous disease problem in storage for a given species.
Label the stored plant material well by writing on the storage bag, writing directly on the bulb with a permanent marker, or by attaching a tag to the root. Include the cultivar name or other important identifying characteristics on the label. You may also want to record the information in a notebook or in some other way to ensure the identity of stored plants is not lost.
Store the dried bulbs between 2 to 3 inch layers of peat moss, sand, vermiculite, sawdust, wood shavings, or coir (coconut husk fiber). Large quantities of tender bulbs can be layered in a ventilated container, such as a cardboard box. Do not pack the bulbs in air-tight containers, which can cause moisture build up and promote decay. Ensure the individual bulbs are not touching, to prevent the spread of rot or decay between bulbs.
The biggest challenge for most gardeners in storing their tender bulbs is finding a spot with the proper temperature. The bulbs should be held in a location with temperatures between 35 and 45 °F and 50% relative humidity. An unfinished basement away from heat sources, a place in an unheated garage that does not freeze, or a root cellar can be ideal, but make sure the area is not too warm or too cold.
Check the bulbs periodically during the winter. Remove any that show signs of rotting (or cut out any damaged tissue of larger tubers) and check the moisture level. If they have dehydrated – with a shrunken or wrinkled appearance – moisten the layering medium a little (such as with a spray bottle) and re-pack them. If they are very moist remove from the packing material and air dry for a few days before repacking in dry material.
Below are more specifics for some commonly grown tender bulbs.
Elephant’s Ear (Alocasia or Colocasia)
Both species can be lifted before frost, potted and treated as a houseplant for the winter. Feed lightly throughout winter and water often. Another option is to clean and store the tubers in peat moss. Check monthly and cut away any soft spots that develop. Allow the remaining healthy portion to dry before re-storing in peat.
Begonias, Tuberous
Dig before a hard frost (a light frost can be allowed to kill the tops). Let the tubers dry for 1 to 2 weeks, with 2 to 5 inches of the foliage left intact. Remove excess soil and foliage and store at 50 °F.
Caladium
Lift caladium plants before frost. Allow them to dry in a warm spot for about a week. Cut back the foliage after it turns yellow. Caladium needs warmer storage temperatures than most other tender bulbs, so store them at 60 °F.
Calla
Dry the rhizomes of calla lilies for 2 to 3 weeks in a warm location, shake off the soil and remove the dried stem. Store at 45 to 55 °F.
Canna
Allow frost to kill the tops, but do not let them be subjected to a hard freeze, which will turn the stem to mush. Dry the roots for a day or two. Cleaned roots can be wrapped in newspaper (or layered in peat moss or other packing material if your storage conditions are dry) and stored in paper bags or cardboard boxes, at 45 to 50 °F. Check periodically to be sure the roots do not dry out; increase the moisture level if necessary. Wait until spring to divide. When dividing, make sure there are at least 3 eyes per division.
Dahlia
Dig before a hard freeze, or let the tops die back from a light frost. Handle the tuberous roots carefully, as they can bruise easily. Although some people prefer to divide the roots immediately after digging, since the eyes or buds are easier to see in the fall, it is best to wait until spring to prevent spoilage in storage. Let them dry for several hours before placing in storage. Check monthly for dehydration and mist lightly, if necessary.
Gladiolus
Lift plants in the fall either when the leaves yellow or after the first frost. Shake off the soil, but do not wash, cut the stems back to 1 to 2 inches, and allow the corms to dry. Place corms in bright sunlight for a day or two, then move them to a well-ventilated location for about 3 weeks to cure. Remove the old, shriveled portion, keeping only the new plump corms, before packing for storage.
Author: Susan Mahr, University of Wisconsin-Madison
Reviewers: Allen R. Pyle, Horticulture Outreach Specialist, UW-Madison Extension, Bruce Spangenberg, Horticulture Outreach Specialist, UW-Madison Extension
Revised: September 2026
