Calla lilies (Zantedeschia species) are prized for their elegant, trumpet-shaped blooms and glossy foliage. Originating from warmer regions of Africa, they cannot survive the freezing temperatures of a temperate winter. Gardeners in colder climates (USDA Hardiness Zones 7 and below) must treat these plants as tender perennials. They need to lift their underground storage organs, the rhizomes, each fall to protect them from frost damage. This ensures the plant enters a cool dormancy and is ready to regrow vigorously when spring returns.
Reading the Signs for Optimal Timing
The decision of when to dig the rhizomes is dictated by both the weather and the plant’s visual cues. The most reliable trigger is the arrival of the first light frost, which signals the end of the growing season. A light frost helps kill the foliage, but the rhizomes must be lifted before a hard freeze can penetrate the soil and cause damage.
Look for signs of natural dormancy in the foliage, which turns yellow, then brown, and eventually collapses entirely. This color change indicates the plant is withdrawing nutrients and energy into the rhizome for winter storage. Waiting until the foliage is fully collapsed maximizes stored energy, promoting better blooms the following year. This generally occurs in late autumn, often between late October and early November, depending on the local climate.
Air temperature is another indicator; digging is necessary when temperatures consistently drop below 50°F (10°C). In warmer regions (Zones 8 and higher), digging may not be necessary for survival if the rhizomes are protected by mulch. However, lifting is sometimes done even in mild climates to divide overcrowded clumps or ensure the plant receives a cool dormant period, which improves flowering performance.
How to Properly Dig and Cure the Bulbs
Once the foliage has died back, cut the dead leaves and stems down to a few inches above the soil line. This remaining stem provides a handle and helps prevent rot from entering the rhizome during storage. Use a garden fork, not a sharp spade, to gently lift the rhizomes from the soil.
Dig widely around the plant, maintaining distance from the stem base to avoid slicing or puncturing the rhizome, which invites disease. After lifting, gently brush off excess soil, but avoid washing them with water. Washing introduces moisture into cuts, significantly increasing the risk of fungal rot during storage.
The next step is “curing,” the final preparation for winter dormancy. Lay the rhizomes in a single layer in a cool, dry, well-ventilated area, away from direct sunlight. An ideal curing temperature is between 60°F and 70°F. Curing allows the outer skin to dry, firm up, and form a protective layer. This period typically lasts five to seven days, though some sources recommend up to two or three weeks for thorough drying.
Essential Steps for Winter Storage
After curing, the rhizomes are ready for long-term storage until spring. The goal is to keep them cool and dry, but safely above freezing and not so dry that they shrivel. An ideal storage temperature range is between 40°F and 50°F to maintain dormancy.
Place the cured rhizomes in a container that allows for air circulation. Do not use airtight plastic containers, as these trap moisture and encourage mold growth. The rhizomes should be nestled in a dry, insulating medium such as:
- Peat moss.
- Shredded newspaper.
- Vermiculite.
- Sawdust.
The medium helps stabilize moisture and prevents the rhizomes from touching, which stops potential rot from spreading. Check the stored rhizomes periodically throughout the winter for signs of mold, rot, or excessive dehydration. If they appear shrunken, a light misting of the storage medium can rehydrate them slightly. They can be replanted in the garden the following spring once all danger of frost has passed.