Extension Educator, Horticulture
The tropical look of cannas and caladiums fit right into the recent trend of colorful bold foliage in garden design. However, these as well as gladiolus and dahlias are seldom winter hardy here. To preserve varieties the bulbous roots need to be dug and stored for replanting next season.
Cannas and Dahlias - Cannas or dahlias should be dug once the leaves have been darkened by frost. They should not be subjected to a hard freeze which turns the stem to mush. Cut the stems back to 4-5 inches and carefully dig the roots with a fork or spade. Let the roots dry for several hours.
Place roots in shallow boxes in dry peat moss, sawdust, vermiculite or sand. Store in a cool, moderately dry area where temperatures are between 35 and 50 degrees such as a basement, crawl space, unheated spare room or a modestly heated garage.
The tuberous roots should not dry and shrivel, so check them periodically during the winter. Sprinkle with water if necessary. In the spring the canna clumps can be divided or planted as a clump. Be sure to include part of the old stem base in each division, since the new growth buds arise from the old stem.
The tuberous roots of dahlias can be divided immediately after digging since the eyes or buds are easier to see in the fall. Each division must have at least one eye.
Gladiolus - The bulb-like corms of gladiolus can also be dug after frost. Shake off the soil and discard any damaged or diseased corms. Cut the tops off 1-2 inches above the corm. The new corms form immediately above the old spring planted corm.
You will notice the zillions of marble sized corms called cormels, which form along the base of the new larger corm. Cormels can also be saved, but they will take 2 to 3 years to bloom. The larger corms will bloom next year.
Dry the corms on paper for one to two days. After drying, place corms on trays or in paper bags, old onion sacks or hose. Store at 35 to 40 degrees F. Do not freeze.
Caladiums and tuberous begonias - Store these similarly to dahlias, but at slightly higher temperatures of 45 to 55 degrees F for begonia and 60 degrees F for caladium.
Geraniums - Garden geraniums can be kept over the winter in a variety of ways starting well before frost. Geraniums don't have a bulb structure so they are not treated in the same way as cannas or dahlias.
One method is to take 3-4 inch stem tip cuttings. Strip off the lower leaves. Dip the cut end in rooting hormone such as Rootone. Stick the cutting in a rooting mixture of sand or a peat moss-perlite mix in a small well drained pot. Water thoroughly and cover the container with a plastic bag and place in a bright area out of direct sun. Cuttings should root in 3 to 4 weeks. After rooting, pot geraniums and grow as houseplants.
Another method is to dig the geranium and pot in potting soil to also grow as a houseplant. Cut the plant back to one-third of its height. The riskiest method is to hang dormant plants upside down in a cool dark place at 45 to 55 degrees. The leaves will yellow and fall off. During the winter, if the plants seem really dry, take them down and soak them in water for an hour or two. In spring, cut stems back and plant in garden after danger of frost or start earlier in pots indoors. The success rate is low with this method.
On Saturday, September 22 at 10:00 am at the Idea Garden on South Lincoln in Urbana Master Gardeners will share ideas for great tools in the garden.