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written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA
published – SEPTEMBER 26, 2014


As weather cools in the fall it is time to plant spring flowering bulbs, but it is also time to dig tender summer flowering “bulbs.” This includes plants with tender bulbs, corms, and rhizomes like dahlia, canna, and gladiolus. The “bulbs” are dug after the first hard frost in the fall and stored over the winter in a place where they stay cool but not freeze.

The best time to dig is about two weeks after the plants are hit by a hard frost, giving the top of the plants a chance to die back. After waiting the two weeks, dig the bulbs, corms or rhizomes up, cut the tops of the plants down to about six inches from the ground. Carefully use a garden fork to lift them out of the ground. Take care not to injure the “bulbs.”

Shake as much soil off the bulbs as possible and then clean the remaining soil off with water from the hose. Again, be careful not to injure the bulbs. The place them in a single layer on newspaper or cardboard and allow them to protected, dry in a dry spot like your garage for a day or two.

Dahlias: Over the summer the dahlia tubers will have developed inot a cluster of tubers. These will be divided in the spring when you go to replant them. Do not cut them into separate tubers before storing them. Place the clusters in single layers in cardboard boxes or paper grocery bags. Start out with a layer of dry sawdust, peat moss, vermiculite, or wood shavings first and then cover the tubers with a generous layer of the same material. Before storing, use a permanent ink marker to write the name of the cultivar directly on several tubers in the cluster, or write it on the bag if you store clusters in individual paper bags. Store the tubers in a cool (40 to 50 degrees F) where the temperature will not go below freezing. Next year’s growth will sprout from the buds that are located at the crown at the base of the old stems.

Canna: Cannas have rhizomes. They are treated pretty much the same as dahlias for digging and storage. The clump of rhizomes can be replanted next spring or divided and replanted. New growth next year develops from buds at the base of this year’s stems.

Gladiolus: Gladioli grow from corms that resemble bulbs. These can be dug after frost kills the leaves or six to eight weeks after all the flowers have faded. These are dryed or “cured” for a longer period of about two to three weeks in a warm (80 degrees F), dry spot out of the sun. When dry enough the old shriveled corms and tiny corms (called cormels) can be easily broken away from the base of the new corms and discarded. Do not remove the protective husks around the corm. Gladiolus corms do not need to be packed in dry materials like sawdust.

Place them in mesh onion sacks or open paper bags to allow for good air movement. Store them under cold (35-40 degrees F) conditions with low humidity where they will not freeze.

This all sounds like considerable effort at a time of year when you are almost happy to see the end of the season. Do you really have to dig and store them every year? Some years dahlias and gladioli may survive if left in the ground, but it is hard to predict when how severe winter will be and replacing all your summer bulbs can be costly. If you cannot bear to lose your summer bulbs, it is best to dig and store them.

Published: 9/26/2014 12:28 PM



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