Extension Educator, Horticulture
Frost doesn't have to mean the end of tender flower bulbs such as cannas, dahlias and gladiolus. Harvesting the bulb-like structures of non-winter hardy plants has its advantages. Hard to find flower varieties can be preserved and it can mean less expense next spring.
Cannas and Dahlias - Cannas or dahlias should be dug once the leaves have been darkened by frost. 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 1 to 2 days. After drying, place corms on trays or in paper bags, old onion sacks or hose. Store at 35 to 40 degrees. Do not freeze.
Caladiums and tuberous begonias - Store these similarly to dahlias, but at slightly higher temperatures of 45 to 55 for begonia and 60 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 1/3 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 the spring, cut stems back and plant in the garden after the danger of frost or start earlier in pots indoors.
Saturday, October 23 at 10:00 am there is a Gardening with Ornamental Grasses workshop at the Idea Garden on South Lincoln in Urbana. While you are there, enjoy the fall festival at the Arboretum with pumpkin carving, hay rack rides, and lectures on flower arranging, squash, fall lawn care and fall tree care.