Calla lilies (Zantedeschia) are tender perennials admired for their elegant, trumpet-shaped blooms and glossy foliage. These South African natives cannot tolerate freezing temperatures, so they require a period of dormancy to survive the winter. Fall is the time to prepare the rhizomes for their winter rest, and the necessary steps depend entirely on your local climate.
Preparing the Plant for Dormancy
The transition to dormancy begins with a subtle shift in your gardening routine during late summer and early fall. To signal the plant that its growing season is concluding, stop all fertilizer applications once the blooms begin to fade. Continuing to feed the plant encourages tender new growth that is vulnerable to cold weather.
Simultaneously, gradually reduce the amount of water the plant receives. This decrease in moisture, combined with cooler temperatures, will naturally cause the foliage to yellow and eventually die back. This process allows the rhizome, the underground storage organ, to absorb and store the maximum amount of energy needed for survival and re-emergence in spring.
Once the foliage has completely withered, or after the season’s first light frost has caused it to collapse, the stems should be cut back. Use clean, sharp shears to trim the leaves down, leaving a small stub of about two to four inches attached to the rhizome. This remaining stem acts as a protective barrier until the rhizome is either lifted or prepared for in-ground overwintering.
Climate-Based Decisions for Winter Survival
The decision of whether to dig up your calla lilies or leave them in the ground hinges entirely on your location’s USDA Plant Hardiness Zone. Calla lilies are reliably hardy only in zones 8 through 11, where winter ground temperatures rarely drop low enough to freeze the rhizomes. Gardeners in these warmer regions can typically leave their plants in place without intervention, provided the area has excellent soil drainage to prevent rot during the wet season.
Conversely, those cultivating calla lilies in zone 7 and any colder zones must lift the rhizomes before the first hard freeze. Freezing temperatures will destroy the fleshy rhizomes, making indoor storage a necessity for perennial growth. Zone 7 is often considered marginal, and lifting the rhizomes is the safest and most recommended practice for guaranteed survival.
Storing Calla Lily Rhizomes
For those who have lifted their plants, the next step is curing the rhizomes for storage. After gently brushing off excess soil, the rhizomes must be allowed to dry in a warm, dry location with good air circulation, ideally at a temperature between 60 and 70°F, for about seven to ten days. This curing process forms a tough, protective outer skin, which significantly reduces the risk of rot during the long dormancy period.
Once cured, the rhizomes should be stored in a cool, dark, and dry environment where the temperature remains consistently between 40 and 50°F. Place the rhizomes in a vented container, such as a cardboard box or paper bag, and cover them with a dry, insulating material like peat moss, vermiculite, or shredded newspaper. This medium prevents the rhizomes from drying out completely while allowing for air exchange, which is paramount to preventing mold and rot.
In-Situ Protection
Gardeners in borderline zones who choose to keep their calla lilies in the ground require in-situ protection. This involves applying a thick layer of organic mulch, such as straw or shredded leaves, approximately four to six inches deep, directly over the planting area. This heavy insulation helps to regulate the soil temperature, providing a buffer against brief cold snaps and protecting the rhizomes from freezing.