Dahlias, tuberous begonias, cannas and caladiums will not survive St. Louis winters outdoors. However, because these plants have specialized underground storage organs such as a tuber, corm or tuberous root, they can be dug up and stored indoors for the winter. In spring, they can be re-planted outdoors.
In fall, dig non-hardy bulbs after the leaves have yellowed, died back or been killed by frost, but before the ground freezes. This provides the longest possible growing season so the plant can store food for next year's growth.
Dig dahlias and cut the tops back to 3 inches above the root. Remove loose soil by hand or with a garden hose and discard all damaged or diseased root portions and place upside down in the sun for several hours to dry. Then, store the roots at 40 degrees F. in a shallow container covered with sand, vermiculite or peat moss. If the roots begin to shrivel during winter, sprinkle them lightly with water.
Tuberous begonias, cannas and caladiums should be dug and air dried in a well ventilated area at 70 to 80 degrees. Cannas and caladiums need one week to dry while tuberous begonias need two to three weeks to dry. Once dried remove any foliage. Cover the tubers and tuberous roots with perlite, vermiculite, peat moss or sand. Store cannas and begonias at 40 to 50 degrees, caladiums at 55 to 60 degrees. All do best stored in a cool, dark and humid place with good ventilation. Fruit cellars and cool basements work well. Do not store bulbs in an attic or garage where they may freeze. Check throughout the winter and discard shriveled, diseased, or insect infested bulbs.
Click here to view the visual guide on digging and storing cannas