Calla Lilies are striking plants that originate from the marshy, warm regions of southern Africa. Their natural habitat means they are sensitive to freezing temperatures and thrive in environments corresponding to USDA hardiness zones 8 through 10. When grown as perennials in colder climates, where the ground freezes consistently, the plant’s natural life cycle requires a forced period of dormancy to survive the winter. Successfully overwintering these tender rhizomes is the only way to ensure their return and flowering capacity in subsequent growing seasons.
Timing and Initial Preparation
The process of preparing calla lilies for winter begins when the plant shows signs of winding down its active growth cycle. This transition usually occurs shortly after the first light frost, which causes the vibrant green foliage to begin yellowing and drooping. Waiting until this point allows the plant to naturally withdraw the maximum amount of stored energy and nutrients back into the underground rhizome structure.
Once the foliage has collapsed or turned fully yellow, it should be cut back to within one or two inches of the soil level using clean shears. This deliberate action signals to the plant that the growing season has ended. Whether the plant is destined to be dug up from the garden or simply moved indoors in its container, this initial preparation step is the same. The shortened stems also make the subsequent handling and storage of the rhizomes or pots significantly easier and reduce the risk of disease transmission during dormancy.
Storing Dug-Up Rhizomes
For calla lilies grown directly in the ground in zones below USDA 8, lifting the rhizomes is necessary. The best time to carefully dig the rhizomes is a day or two after the foliage has been cut back, ideally when the surrounding soil is relatively dry. Using a garden fork, the rhizomes should be gently lifted from the soil, taking care not to damage the delicate outer layer which can introduce pathogens.
After lifting, the rhizomes must undergo a “curing” period to dry the exterior and prevent fungal rot. The rhizomes should be placed in a single layer in a warm, dry location with good air circulation, such as a garage or protected porch. This curing process should last for approximately five to seven days, allowing the outer skin to completely dry and slightly harden.
Once cured, the rhizomes are ready for long-term storage in an environment that maintains cool, stable temperatures, generally between 40 and 50 degrees Fahrenheit. The rhizomes should be packed loosely in a breathable material that prevents moisture accumulation and provides insulation. Suitable materials include dry peat moss, vermiculite, or even shredded newspaper placed inside paper bags or cardboard boxes. The storage container should remain open or have holes to ensure a constant exchange of air, which is fundamental for maintaining dormancy.
Managing Potted Plants
Container-grown calla lilies offer a simplified approach to winterization. To initiate dormancy, the gardener must drastically reduce the frequency of watering once the cooler autumn temperatures arrive. This moisture stress mimics the natural dry season in their native environment, prompting the plant to halt active growth.
Following the reduction in water, the foliage is cut back to just above the soil line, similar to the preparation for in-ground rhizomes. The potted plant can then be moved to a cool, dark location, such as an unheated basement or a protected garage. The temperature in this storage area should be maintained within the 40 to 50 degrees Fahrenheit range to keep the plant dormant.
During the dormancy period, the soil should be checked infrequently to ensure it does not completely desiccate, which would damage the rhizome. A slight misting of the surface soil once a month is usually sufficient to maintain just enough moisture. Avoid any substantial watering that could encourage the rhizome to break dormancy too early.
Waking Up and Replanting
The winterization cycle concludes when favorable growing conditions return. Stored, bare rhizomes should first be inspected closely for any signs of decay, and any damaged sections should be discarded. Healthy, firm rhizomes are then ready to be planted in fresh, sterile potting mix indoors.
The potted plants should be brought out of their dark location and placed in a bright area, though initially protected from direct, intense sunlight. Watering should be gradually increased to encourage the rhizome to break dormancy and begin producing new shoots. This slow transition prevents the plant from experiencing shock and promotes robust, healthy growth from the stored energy reserves.
Once new growth is established and all danger of frost has passed, the plants can be moved outdoors. Plants that started indoors benefit from a process known as ‘hardening off,’ where they are gradually exposed to outdoor conditions over a period of one to two weeks. This acclimatization, which includes periods of sun, wind, and cooler night temperatures, prevents leaf scorch.