Gladiolus, with their towering flower spikes and vibrant summer colors, are a popular addition to many gardens. Proper post-flowering care is essential for maximizing the health and vigor of the underground corm, the plant’s main storage organ. Ensuring the plant can gather and store sufficient energy after the petals drop helps produce a magnificent display the following year. This care involves two phases: removing the spent flower spike and allowing the remaining leaves to function fully.
Removing the Spent Flower Spike
The first post-flowering action is to remove the spent flower spike, a process known as deadheading. Once the individual florets have wilted, the entire spike should be cut off cleanly above the remaining foliage, taking care not to damage the leaves.
Removing the flower spike serves a dual purpose for the plant’s energy management and overall appearance. If the spike remains, the plant attempts to produce seeds, diverting significant energy away from the underground corm. Cutting the spike redirects this energy toward strengthening the corm for the following season’s growth and bloom.
Deadheading also improves the aesthetics by removing unsightly brown or dried flower stalks. Removing the spent spike is the only immediate cutting action that should be taken after the bloom period concludes.
Why Foliage Must Remain
While the flower spike is removed immediately, the sword-like green foliage must remain intact for an extended period. The leaves perform photosynthesis, converting sunlight into carbohydrates needed for survival and future growth. These carbohydrates are then transported down to the corm for storage.
Prematurely cutting the leaves severely depletes the corm’s energy reserves. The corm requires this period of energy replenishment following the intense effort of producing a flower stalk. This carbohydrate storage phase determines the size and quality of the next season’s blooms.
Gardeners should allow the foliage to photosynthesize for approximately six to eight weeks after the last flower has faded. The leaves will naturally yellow and die back as the plant completes the energy transfer process. Only when the foliage has completely turned yellow or brown and is easily pulled away from the corm should it be removed, typically cut back to about 1 to 2 inches above the soil line.
Preparing Corms for Dormancy
Once the foliage has fully died back, the corms must be prepared for winter dormancy, particularly in regions where the ground freezes (USDA Zones 7 and below). The first step is carefully lifting the corms from the soil using a garden fork to avoid damaging the underground structure. The corms should then be gently shaken to remove excess dirt.
The corms need a curing period to dry out and harden their outer layers, which prevents rot during storage. Place them in a warm, dry, and well-ventilated area, such as a garage or shed, for about two to three weeks. Temperatures should ideally range from 70°F to 80°F to ensure the protective husk is firm and dry.
Following curing, the old, shriveled mother corm at the bottom can be removed and discarded, as a new, larger corm has formed above it. This is also the time to separate small offsets, called cormels, which can be saved to grow new plants. Dusting the corms with a fungicide or insecticide powder prevents common storage pests like thrips and fungal diseases.
The cleaned and treated corms should be stored in a cool, dry location with good air circulation to maintain dormancy. Ideal storage temperatures range from 35°F to 45°F, often achievable in a cool basement or insulated garage. Placing the corms in mesh bags, paper bags, or open trays prevents moisture buildup and ensures viability until replanting the following spring.