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Chicago Urban Gardening

The day to day experiences of a University of Illinois Extension Urban Horticulture Educator in Chicago, Illinois

Time to Dig Up Tender Flowering Bulbs

Posted by Ron Wolford -

Tender flowering "bulbs" produce some of our most colorful summer blooms. Gladiolus, canna, tuberous begonia and others are commonly grown throughout the U.S.

"These plants need special care because freezing kills them," says David Robson, University of Illinois Extension horticulture educator.

The bulbs (in reality tubers, rhizomes and corms, in addition to true bulbs) need to be dug up and stored indoors just like potatoes, onions and carrots. Robson says harvesting these bulbs takes the same care as vegetable harvesting.

While the different flowering plants require different handling techniques, they all require the same care in handling.

Gladioli grow from corms. The corms should be dug once the foliage has matured or after frost. Carefully lift the corms from the ground to avoid losing the small cormels that will be future glads.

Cut the tips an inch above the corms and cure the corms for two to four weeks in a warm spot with good air circulation. Brush off any dried soil with a soft cloth. Remove the old shriveled corm on the bottom of the new tan one.

Before storing the corms, dust them with an insecticide-fungicide mixture to prevent the corms from rotting and to control thrips. Store the corms in onion bags or old nylon stockings hung in a place with good air circulation and temperatures from 35 to 45 degrees.

Dahlias grow from tubers. Cut dahlia tops back to within 3 to 4 inches of the soil after the first frost. Dig carefully to avoid damaging the fleshy roots or breaking off the new eyes. Cure dahlias the same way as glads for one to three days. Keep as much of the soil attached as possible.

Store dahlias in a box or plastic bag packed with vermiculite, peat moss or wood chips to prevent drying out. Dahlia tubers should be completely covered and stored at 35 to 45 degrees.

"The tubers should be inspected several times throughout the winter," says Robson. "If they start to shrivel, lightly sprinkle the packing material with water. If conditions are too moist and roots start to rot, move the tubers to a drier place and remove rotted portions."

Treat canna roots similar to dahlia, except store them upside down in a shallow box. Cannas do not require covering. Hold the roots in 45- to 50-degree storage temperatures.

Tuberoses should be cut back after frost and their bulbs stored in sand or vermiculite-filled plastic bags at 55 to 60 degrees.

Peruvian daffodil bulbs should be dug before frost and stored upside down in vermiculite or dry sand. Store at the same temperature as tuberoses.

Check bulbs, tubers, corms and roots throughout the storage season and make any necessary changes in their conditions so that they will make it through the winter in good shape.

Source: David J. Robson, Extension Educator, Horticulture,

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