September 18, 2002
Woodbury Bulletin
Betsy Halden

Winter storage of tender perennials

Perennials are generally divided into two groups. Hardy perennials are those plants that will withstand our Zone 4 winters when temperatures may dip to minus 30 F. Tender perennials are those plants that will not survive our harsh winters if left outdoors. Tender perennials such as tuberous begonias, caladium, gladiola, calla lilies, canna, and dahlias are popular in our area. These tender perennials should be dug in the fall and stored indoors until time for spring planting.

Tuberous begonias, Begonia xtuberhybrida, come in a wide assortment of colors and types. Flower forms include camellia, cascade, carnation, picotee, and non-stop series. Tuberous begonias grown in containers can be brought indoors for winter months. Those tubers left outside should be dug after a killing frost. To properly condition the tubers for storage, place them in a warm, dry location of approximately two weeks. Then bury the tubers in a box or sack filled with sphagnum moss or vermiculite. Store them in a cool, dry location.

Caladium, Caladium xhortulanum, is a great plant to grow in shade. Caladium is grown for its colorful foliage rather than its flowers. When the foliage dies back in the fall, carefully lift the tubers out of the soil and find a warm, dry place to cure them. Typically the process is complete in two weeks. Store the tubers in dry sand, vermiculite, or sphagnum moss in a cool (50 degrees F), frost-free area.

Gladiolus, Gladiolus hybrids, is striking in flower beds and in flower arrangements. But gladiolus can’t be left outside during Minnesota winters. The gladiolus, or glad, develops from a growing structure, a corm. A corm is a short, thickened underground stem where food is stored. When the gladiolus foliage has yellowed, lift the corms carefully, cut off the foliage 1 to 2 inches above the corm, and allow it to dry for a week in a sunny location. Corms can be treated with a fungicide to prevent disease while in storage. Remove and discard the remains of the old mother corm located at the bottom of the large, healthy corm. Place the corms in old onion sack or nylon stocking. Store the corms in a cool, dry, frost-free location until planting time in the spring.

Though calla lilies, Zandedeschia spp., are tropical in appearance, they can be grown successfully in our area. After the foliage has been damaged by frost, cut off the tops about 2 inches above the soil line. Dry the calla rhizomes in a warm, dry location for one or two weeks. Bury the rhizomes in vermiculite, sawdust, or peat moss, and store in a cool (45 to 55 degrees F), frost-free area.

The large, banana-like foliage of the canna, Canna xgeneralis, can’t be missed in the garden. Some cannas grow to about six feet in height, while others top the two to three-foot range. After a killing frost, cut the stems back to 3-4 inches above the soil. Carefully dig up the rhizomes, let them dry for a few hours, then place them in crates or mesh bags. Store at 35 to 45 degrees F.

Dahlias, Dahlia hybrids, are standouts in the summer garden. With more than 40,000 varieties to choose from, it’s easy to have several favorite varieties of dahlia in our garden. After a killing frost has destroyed the foliage, cut away the top of the dahlia, carefully dig the tuber, and label it with the variety name. Wash the tubers with water to remove as much soil as possible. This lessens the chance for soil insects to destroy the tubers while in storage. Dry the tubers in a site out of direct sunlight and protected from strong winds. When the tubers become dry to the touch, remove any portion of the stalk that remains and place the tubers upside down in vermiculite to ensure that any remaining water in the crown tissue drains out.

“Storing Tender Bulbs and Bulblike Structures” is the title of a Fact Sheet published by the University of Minnesota Extension Service. You can access it a www.extension.umn.edu and enter the title in the search box.

On Monday, September 23, the Washington County Horticulture Society (WCHS) will hold its monthly meeting at Oak-land Junior High, Manning Avenue, Highway 15, 1/2 mile north of I 94, Lake Elmo. The meeting includes the fall plant sale which is open to the public at 6:45 pm. At 7:30 pm, Kirke Northcutt, Executive Chef, University of Minnesota Hubert H. Humphrey Institute, will talk on “Cooking with Herbs.” All interested gardeners or cooks are invited to attend.

Betsy Halden is a resident of Woodbury. University of Minnesota Extension Service and Iowa State University Extension Service materials were consulted in the preparation of this column. You can reach Betsy Halden at eahalden@comcast.net.