Calla lilies, botanically known as Zantedeschia species, are visually striking plants recognized for their elegant, trumpet-shaped spathes. These flowers are classified as tender perennials, meaning their fleshy, underground storage organs, called rhizomes, cannot tolerate freezing temperatures. In climates outside of the mildest USDA Zones, typically 8 or 9 and warmer, calla lilies must be managed to survive the winter. This management involves inducing a necessary period of dormancy to protect the rhizomes from frost and prepare them for renewed growth in the following spring.
Preparing Calla Lilies for Dormancy
The preparation phase for winter dormancy applies to all calla lilies, regardless of whether they are planted in the ground or kept in containers. Initiate this process by gradually withholding water and stopping fertilizer application once the flowering season concludes in the late summer or early fall. This reduction in resources signals to the plant that it is time to slow its growth cycle and transfer energy reserves back into the rhizome.
The foliage should be allowed to naturally yellow and wither completely before any cutting occurs. This natural senescence is a crucial step, as the dying leaves actively transport stored carbohydrates back down to the rhizome, building up the energy reserves needed to survive the dormant period. Once the leaves have fully browned and dried, often triggered by the first light frost, cut the spent foliage back to about two to three inches above the soil line.
Winterizing Potted Calla Lilies
Winterizing container-grown calla lilies allows the rhizome to remain undisturbed in its original pot. After the foliage has been cut back, the container should be moved to a protected location before the onset of hard frost. The goal is to provide a cool, dark, and dry environment for the duration of the winter rest period.
A garage, unheated basement, or cellar works well, provided the temperature remains consistently above freezing. The optimal temperature range for container storage is between 40 and 50 degrees Fahrenheit, which is cool enough to maintain dormancy. During this time, completely cease watering the potted rhizomes to prevent them from rotting in the cold, damp soil. The pot should remain untouched until spring.
Winterizing In-Ground Calla Lilies
In colder regions, calla lily rhizomes planted directly into the garden must be dug up and stored indoors for winter protection. This process should be undertaken after the foliage has died back following the first light frost. Begin by carefully digging around the clump using a garden fork, starting several inches away from the plant’s center to avoid damaging the rhizome.
Once lifted, gently brush off the majority of the clinging soil, taking care not to wash the rhizomes, as excess moisture can encourage rot during storage. Any sections that are cut or appear damaged should be dusted with a fungicide or garden sulfur to protect the exposed tissue from pathogens. The cleaned rhizomes must then be cured by placing them in a single layer on a rack or tray in a dry, well-ventilated area for several days. Curing at a temperature between 60 and 70 degrees Fahrenheit allows the exterior skin to dry and harden before long-term storage.
Post-Winterization Storage and Care
After the in-ground rhizomes have been cured, or once the potted plants have been moved, attention shifts to maintaining the long-term storage environment. The dug-up rhizomes should be stored in a ventilated container, such as a paper bag, cardboard box, or mesh bag, to ensure adequate air circulation. To prevent desiccation and provide a buffer, the rhizomes should be layered in a dry, inert medium like peat moss, vermiculite, or sawdust.
The chosen storage location, whether holding potted or loose rhizomes, must remain cool, dry, and frost-free throughout the winter. Regularly inspecting the stored rhizomes every few weeks is important to monitor for signs of mold, rot, or excessive drying. If the rhizomes appear shriveled or overly dry, the storage medium can be lightly misted, but moisture should be kept to a minimum to avoid breaking dormancy prematurely. Potted plants should remain completely dry and undisturbed in their dormant state until the time for spring repotting and watering arrives.