From the plant's perspective, the Gladiolus is not a true bulb but a corm, a swollen, solid stem base that serves as a storage organ. As autumn approaches and daylight diminishes, the plant receives environmental signals that the growing season is ending. The drop in temperature and reduced photoperiod trigger a hormonal shift within the plant, primarily an increase in abscisic acid, which initiates senescence. The plant's priority shifts from above-ground growth and flowering to conserving energy. It begins to translocate valuable nutrients and carbohydrates from the dying foliage down into the corm. This process is vital for storing the energy required to survive winter dormancy and fuel next season's growth. Digging up the corms before this process is complete would starve them of these essential reserves.
The optimal time to dig is not dictated by a specific date but by the plant's physiological state. You must wait until the foliage has begun to yellow and die back naturally, typically after the first light frost in autumn but before a hard freeze. This visual cue indicates that the nutrient transfer back to the corm is largely complete. If you cut back green foliage too early, you interrupt this critical process, resulting in a weak corm with insufficient energy stores. Conversely, waiting too long, especially after a hard frost (below 25°F or -4°C), risks damage to the corm itself. The cold can cause cell walls to rupture, leading to rot during storage. Therefore, the plant tells you when it is ready: when its leaves have turned brown and it has entered its dormant state.
When digging, the plant's underground structure must be considered. Use a garden fork or spade to gently loosen the soil in a wide circle around the plant, taking care not to pierce or bruise the corms. Gladiolus corms often produce new, smaller corms called cormels around their base; these are genetic offspring that can be grown into new plants. Gently lift the clump of corms and soil and shake off the excess dirt. Do not wash the corms with water, as this can promote fungal growth. Instead, leave the soil to dry. At this stage, the plant is still respiring and needs to cure. With the foliage still attached, place the corms in a warm, dry, and well-ventilated area out of direct sunlight for about two to three weeks. This curing process allows the outer layers of the corm to dry and form a protective sheath, and allows the remaining nutrients in the foliage to be fully absorbed.
After the curing period, the plant is fully dormant. Now, you can finish the preparation. Remove the dried foliage by cutting it off about an inch above the corm. Gently separate the new corms (cormels) from the old, shriveled parent corm, which will be discarded. Inspect each corm carefully for any signs of disease, soft spots, or damage; only firm, healthy corms should be stored. To protect against rot and thrips during storage, you may choose to dust the corms with a fungicide or food-grade diatomaceous earth. This mimics a protective barrier the plant might develop in a perfectly dry, pest-free natural environment.
To successfully maintain dormancy and preserve the plant's vitality, storage conditions must replicate a cool, dry winter. Place the cured corms in mesh bags, paper bags, or cardboard boxes with some dry peat moss, vermiculite, or wood shavings to absorb excess moisture. The storage location should be dark, with good air circulation, and a consistent temperature between 35°F and 45°F (2°C and 7°C). This cool temperature is crucial as it keeps the plant dormant without inducing cold damage. Storing them in a warm location would signal an early end to dormancy, causing premature sprouting and depleting energy reserves before it's time to plant again in the spring.
