Gladiolus, often called “glads,” are summer-blooming flowers known for their tall spikes of colorful blossoms. These plants grow from underground storage organs called corms, which function similarly to bulbs. Because gladiolus corms are tender and susceptible to freezing temperatures, they require specific end-of-season attention to ensure survival and rebloom the following year. This preparation involves timing the cutting back of foliage, deciding on a wintering strategy, and following steps for corm removal and storage.
The Critical Timing for Cutting Back Foliage
The timing for cutting back gladiolus foliage is tied to the corm’s ability to store energy for the next growing season. After the flower spike has finished blooming, resist the urge to cut the leaves back immediately. The remaining green foliage must photosynthesize, sending carbohydrates down to the corm for nourishment and maturation.
This energy transfer process typically requires about six to eight weeks after the flowers have faded. Once the leaves naturally begin to yellow and wither, the corm is ready for dormancy preparation. The foliage should then be cut back, usually to a height of two to three inches above the soil line, ideally before a hard frost arrives.
Determining Your Winter Strategy
The decision of whether to leave gladiolus corms in the ground or dig them up for storage is dictated by your local climate. Corms are considered hardy only in warmer regions, specifically USDA Hardiness Zones 8 through 10. Gardeners should identify their zone to determine the necessary winter care.
If you reside in Zone 8 or above, the corms can remain in the soil throughout the winter. In these areas, apply a thick layer of protective organic mulch, like straw or shredded leaves, over the planting bed to insulate the soil from temperature fluctuations. For those in colder areas, Zone 7 and below, freezing temperatures will destroy the corms, making removal and indoor storage mandatory for overwintering.
Step-by-Step Corm Removal and Curing
For gardeners in cold climates, corm removal should be timed just after a light frost has withered the foliage, but well before the ground freezes solid. Carefully lift the corms from the soil to avoid damage, using a garden fork inserted wide of the plant clump. Gently loosen the soil, allowing them to be pulled out by the remaining stalk.
Once lifted, shake or brush excess soil off the corms. Trim the remaining stem down to a short stub, about one to two inches above the corm itself. The corms must then undergo a curing process to harden the outer layers and prevent rot during storage. Curing involves placing the corms in a single layer in a warm, dry, well-ventilated location, such as a garage or shed, for two to three weeks.
After the initial drying period, the corms are ready for cleaning and division. The withered “mother” corm from the previous year, located at the base, should be removed and discarded. Small cormlets, or offsets, that have formed around the new corm can be separated and saved for propagation, though they will take a few years to reach flowering size. Inspect the new corms for signs of disease, such as soft spots or mold, and discard any that appear unhealthy to prevent pathogen spread.
Proper Winter Storage and Replanting Preparation
After the corms are fully cured and cleaned, they require specific conditions to maintain dormancy throughout the winter months. The ideal storage location should be cool, dark, and dry, with a consistent temperature range between 35°F and 45°F. This cool temperature prevents the corms from sprouting prematurely before spring arrives.
Adequate air circulation is required to prevent moisture buildup and subsequent mold or rot. Corms should be stored in breathable containers, such as mesh bags, paper sacks, or open cardboard boxes, avoiding sealed plastic containers entirely. Check the stored corms periodically during the winter to remove any that show signs of decay or shriveling. Before replanting in the spring, dusting the corms with an anti-fungal powder offers protection against soil-borne diseases.