Storing bulbs over winter is a necessary practice for gardeners who wish to preserve their summer-flowering plants in cold climates. Overwintering protects tender underground structures, such as bulbs, corms, tubers, and rhizomes, from freezing temperatures. Many popular garden plants originate from tropical or subtropical areas, meaning their underground parts cannot withstand soil freezing and subsequent damage. This annual process of lifting, curing, and storing these tender structures indoors allows the plants to enter dormancy, ensuring their survival and continued bloom the following spring.
Identifying Bulbs That Require Lifting
Garden bulbs are categorized into two groups based on their winter hardiness. Hardy bulbs, including tulips, daffodils, and crocuses, tolerate cold and remain in the ground through winter, often requiring the cold period for proper spring blooming. Conversely, tender bulbs lack cold tolerance and will perish if left in frozen soil. Varieties such as dahlias, gladiolus, cannas, and tuberous begonias must be removed before sustained freezing conditions begin. The optimal time for lifting is after the first light frost, which signals dormancy by killing the above-ground foliage, allowing the bulb or tuber to store its final energy reserves.
Preparing Bulbs for Storage
The first step after lifting a bulb or tuber is to remove excess soil and trim the remaining foliage. Use a garden fork for digging to minimize damage to the underground structures, as any injury can provide an entry point for disease and rot. Cut the foliage back, typically leaving a short stem of one to two inches attached to the structure.
The crucial next phase is curing, which dries the outer layer to create a protective, hardened skin. This process reduces internal moisture content, preventing fungus and mold during long-term storage. Bulbs should be spread in a single layer in a dry, well-ventilated area, away from direct sunlight, with temperatures between 60°F and 70°F. While many bulbs cure within a few days, some varieties like gladiolus may require up to three weeks to fully dry before storage.
Establishing the Storage Environment
The long-term storage location must consistently maintain cool, dark, and slightly humid conditions to prevent desiccation and premature sprouting. A common storage temperature range for most tender bulbs is between 35°F and 50°F, though some tropical types may require temperatures closer to 60°F. Acceptable locations include an unheated basement, a cool root cellar, or an insulated garage that remains above freezing. Relative humidity should ideally be maintained around 50% to discourage the bulbs from drying out.
The final step involves packing the cured bulbs in a breathable storage medium. Materials such as peat moss, vermiculite, sawdust, or shredded newspaper are used to insulate the bulbs, absorb minor moisture fluctuations, and prevent physical contact between them. Bulbs should be arranged in layers within ventilated containers, such as cardboard boxes or paper bags, ensuring that no two bulbs touch, which significantly reduces the risk of spreading rot or fungal infection.
Monitoring Bulbs During Winter
Although dormant, bulbs require periodic checks throughout the winter months to ensure they remain healthy. Monthly monitoring is recommended to proactively identify and address common storage problems.
If bulbs appear shriveled or wrinkled, the environment is likely too dry or warm, and the packing medium needs to be lightly misted to restore moisture. Conversely, mold, soft spots, or sliminess suggests the environment is too damp or lacks adequate air circulation. Any affected bulbs must be immediately removed and discarded to prevent the spread of rot to adjacent stock. If only slightly affected, they can sometimes be dried out and repacked in fresh, dry medium. Maintain vigilance over temperature, humidity, and ventilation until late winter or early spring before preparing the bulbs for replanting.