Gladiolus plants (Acidanthera or Gladiolus spp.) grow in most U.S. Department of Agriculture hardiness zones but can only remain in the ground year-round in zones 7 through 10, which rarely experience hard frost. Digging and storing the corms, which are similar to bulbs, protects them from frost in cooler regions. But even in mild and warm climates, lifting and storing corms improves flowering the next summer, because stored corms are more likely to remain dormant for the correct period.
The flowering period depends on the gladiolus variety, but most types are dug in autumn after flowering completes and the foliage begins to yellow. In areas that experience frost, the gladiolus corms require digging before the first hard frost in fall or early winter. The corms can't survive if they freeze, although a light frost rarely freezes the soil. In areas that don't experience frost, dig the corms either when the foliage yellows and begins to die back or six weeks after flowering completes.
Damage to delicate gladiolus corms can kill them before you have a chance to store them. Loosening the soil around the base of the plant with a cultivating fork or trowel allows you to lift them by hand and minimizes damage. You can cut down the foliage either before or after digging, but leave no more than 2 inches attached to the corms. Soil may cling to the corms, but avoid washing it off, because wet corms are more prone to fungal problems in storage. Instead, allow the soil to dry on the corms and brush it off prior to storage.
Gladioli produce small cormels on the main corm. These cormels can grow into new plants if properly removed and stored. Divide the cormels after digging up the gladiolas. These corms break off the main corm easily with just a gentle twist. Dispose of any smaller than 1 inch in diameter, because these likely won't flower. Also dispose of any corms that have visible damage, look withered and dry or have soft spots that indicate rot. Corms with visible fungal infections or other signs of disease also won't survive storage, and they may infect healthy corms.
Dry peat moss or vermiculite provides a sterile storage medium for gladiolus corms. Fill a shallow box or a cloth bag with the storage medium. Dusting the corms with a bulb fungicide prior to storage prevents disease issues during storage. Store the corms buried in the dry medium, arranging them so that they don't touch one another. A cool, dry location that isn't exposed to freezing temperatures supplies the optimum storage conditions.
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