When gladiolus flower spikes fade, gardeners often wonder how to treat the remaining foliage. The answer is twofold: immediately cut the spent flower stalk, but do not cut the green foliage down. Proper post-bloom maintenance is necessary to ensure the underground storage structure, known as the corm, can regenerate and produce magnificent blooms the following season.
Cutting Back the Spent Flower Spike
The immediate action after the last bloom wilts is to remove the spent flower spike, a process often called deadheading. This stops the plant from diverting energy into producing seeds, which is a metabolically expensive process. If left on the stem, developing seed pods consume energy needed to nourish the corm below ground. Use clean, sharp shears or a knife to make a precise cut to remove the stalk.
The spent flower spike should be removed just above the uppermost leaves still attached to the main stem. Leaving a minimum of four sets of leaves attached is important for the plant’s health. This attached foliage remains actively photosynthesizing, ensuring continued nourishment for the corm. This action redirects the plant’s focus back to energy storage.
Why You Must Keep the Leaves
The green foliage acts as the plant’s food factory through photosynthesis. This process converts sunlight into the complex sugars, or carbohydrates, the plant requires to replenish its corm. The corm must store sufficient energy reserves to survive winter dormancy and initiate new growth the following season.
Cutting the leaves before they naturally yellow interrupts this essential energy transfer process. When the leaves are removed prematurely, the corm does not receive the necessary carbohydrate reserves for rejuvenation. This results in a smaller, weaker corm that lacks the stored power to produce a flower spike the next year.
The foliage must remain attached and green for approximately six to eight weeks after the bloom fades. This extended period allows for maximum energy accumulation before the leaves naturally turn yellow. Only once the leaves have completely yellowed and withered, indicating the corm has absorbed all available nutrients, has the cycle of energy storage concluded.
Storing Gladiolus Corms for Winter
For gardeners in cold regions (USDA zones 7 and below), the corms must be lifted and stored indoors to survive winter temperatures. The ideal time for digging is when the foliage has fully yellowed or after the first light frost has caused the leaves to collapse. Carefully loosen the soil around the plant using a garden fork to avoid damaging the corm structure when lifting.
Once lifted, the corms need a period of curing, which involves drying them in a warm, dark, and well-ventilated area for two to three weeks. During this time, the attached foliage should be cut back to about an inch above the corm. Curing allows the outer layers of the corm to harden, which helps prevent rot during storage.
After curing, the old, shriveled “mother” corm and any remaining roots should be gently separated from the newly developed, firmer daughter corm. The cleaned corms can optionally be dusted with a commercial fungicide or sulfur powder to deter fungal pathogens and pests. Store the prepared corms in mesh bags or open trays, ensuring they are kept in a cool, dry, frost-free location with temperatures consistently maintained between 35°F and 45°F.