The gladiolus grows from a bulb, known as a corm, a bulbous, swollen, underground stem that supplies the plant with valuable nutrients. During the summer months a new corm forms directly on top of the old corm, which withers away as its nutrients deplete. The new corm must be lifted before the harsh winter months and stored to ensure the gladiolus' survival for spring planting. Smaller corms also form around the main corm. Divide and store the smaller corms to ensure propagation. Transplant the smaller corms to new locations the following spring.
Dig up gladiolus corms after the first frost in fall. Use a garden spade and gently dig around the perimeter of the plant.
Grasp the foliage of the gladiolus plant at the base, beside the soil level. Gently lift the plant from the soil once the corms have been exposed through digging.
Shake the soil from the corms. Examine the corm closely to determine its health. It should show no discolouration, soft spots or areas of fungus. Discard any corm that is soft, mushy or shows discolouration.
Clip the top foliage 2 inches away from the corm using a pair of hand shears. Discard the top foliage.
Pry away the small corms around the base of the large corm to store separately. The small corms may not flower immediately the following season after planting but require two or more years to reach an adequate size to produce blossoms.
Spread the corms out on a dry towel in full sunlight. Allow the corms to adequately dry over days.
Place the corms in a tray. Store the bulbs for three weeks in a room with a temperature of 26.7 to 29.4 degrees Celsius, according to Purdue University.
Break away the old corm from the underpart of the new corm. Discard the old, shrivelled corm.
Dust the gladiolus corms with a bulb fungicide for bulb storage. A wide variety of bulb fungicides are available at garden supply stores. Follow the directions on the label for application.
Place the corms in a paper bag. Store the corms in an area that is dry. The temperature should remain 35 to 40 degrees Fahrenheit throughout the winter.
Plant the gladiolus bulbs outside in the spring after all danger of frost has passed. Corms begin to produce flowers when they reach two to three years of age. Corms produce the best flowers during their first six years of flowering, and then flowering begins to decline, according to the University of Missouri. Plant gladiolus corms in well-draining soil to prevent possible rotting from occurring. Gladiolus bulbs grow best in full sunlight.
Never allow the gladiolus bulbs to freeze.