Calla lilies (Zantedeschia spp.) are tender perennials native to South Africa, where they thrive in warm, moist conditions. In cold climates, they enter a natural dormancy phase as temperatures drop. This is a survival mechanism to conserve energy during unfavorable conditions. As a plant, we sense shorter daylight hours and cooler temperatures, signaling us to redirect nutrients from foliage to underground rhizomes. This process is crucial for overwintering success, as it ensures we have enough stored energy to regrow in spring.
As autumn approaches and temperatures consistently fall below 50°F (10°C), our leaves begin to yellow and wilt. This is your cue to start overwintering preparations. Resist the urge to cut back foliage immediately; instead, allow us to naturally withdraw nutrients. Premature cutting can weaken our rhizomes, reducing next season's blooms. Once frost arrives and our foliage turns brown, it’s safe to trim stems to 2–3 inches above the soil.
In regions where ground temperatures freeze, leaving us in the soil is fatal. Carefully dig up our rhizomes using a garden fork, avoiding damage to the fleshy storage organs. Shake off excess soil but do not wash us, as moisture can invite rot. Let us air-dry in a shaded, well-ventilated space for 1–2 days to toughen our outer layer. This step mimics the dry season in our native habitat, hardening us for storage.
Store our rhizomes in a cool (40–50°F / 4–10°C), dark, and dry environment—similar to a South African winter. Place us in a breathable container, such as a cardboard box or mesh bag, layered with slightly moist peat moss or vermiculite. Avoid sealing us in plastic, as trapped humidity causes mold. Check monthly for shriveling (add a spritz of water) or rot (remove affected parts). We remain dormant but alive, relying on stored starches until spring.
If grown in containers, you can move our entire pot indoors after trimming foliage. Keep the soil barely moist and store us in a dark, cool basement or garage. This method reduces transplant shock in spring. Alternatively, in milder cold climates (USDA Zone 8), a thick mulch layer (6+ inches of straw or leaves) may insulate our rhizomes in-ground, though this risks rot in wet winters.
As daylight increases and frost danger passes, reintroduce us to warmth and light. Replant rhizomes 3–4 inches deep in well-draining soil after the last frost. Water sparingly until new growth emerges, then increase moisture gradually. We’ll use our stored energy to push out new leaves and flowers, completing the overwintering cycle.
