Calla lily bulbs, technically rhizomes, are underground storage organs that store nutrients and energy for the plant. These structures are crucial for growth, as they contain dormant buds that sprout into stems, leaves, and flowers. To maximize growth, it's essential to select healthy, firm bulbs free of mold or soft spots. Larger bulbs typically produce more robust plants with abundant blooms.
Calla lilies thrive when planted in early spring after the last frost, as they prefer warm soil temperatures (around 60–75°F or 15–24°C). Planting too early in cold soil can cause rot, while late planting may delay flowering. In warmer climates (USDA zones 8–10), bulbs can be left in the ground year-round, but in colder regions, they should be lifted and stored over winter.
Calla lilies demand bright, indirect sunlight for optimal growth. In hotter climates, partial shade prevents scorching, while in cooler regions, full sun encourages vigorous blooming. The planting site should have well-draining soil to prevent waterlogged conditions, which can lead to bulb rot. If the soil is heavy clay, amend it with compost or sand to improve drainage.
Rich, slightly acidic to neutral soil (pH 6.0–6.5) is ideal for calla lilies. Before planting, loosen the soil to a depth of 12 inches (30 cm) and mix in organic matter like compost or aged manure. This enhances fertility and aeration, allowing roots to spread easily. Avoid high-nitrogen fertilizers, which promote leafy growth at the expense of flowers.
Plant bulbs 4–6 inches (10–15 cm) deep with the growing tips facing upward. Space them 12–18 inches (30–45 cm) apart to ensure adequate air circulation and prevent overcrowding. Proper spacing reduces competition for nutrients and minimizes disease risk. In containers, use a well-draining potting mix and ensure the pot has drainage holes.
After planting, water the bulbs thoroughly to settle the soil. Keep the soil consistently moist but not soggy during the growing season. Reduce watering once flowering ends to allow the bulbs to enter dormancy. Overwatering can cause rot, while underwatering stresses the plant, leading to stunted growth.
Feed calla lilies with a balanced, slow-release fertilizer (e.g., 10-10-10) at planting time and again every 4–6 weeks during active growth. Alternatively, use a phosphorus-rich fertilizer to boost blooming. Stop fertilizing after flowering to let the plant prepare for dormancy.
Apply a 2–3 inch (5–7 cm) layer of mulch (e.g., straw or bark) to retain moisture, regulate soil temperature, and suppress weeds. In colder zones, mulch heavily in fall to protect bulbs from freezing. Calla lilies are sensitive to frost; temperatures below 50°F (10°C) can damage foliage and bulbs.
After flowering, allow foliage to yellow and wither naturally—this process helps bulbs store energy for the next season. In frost-prone areas, dig up bulbs before the first frost, dry them for a few days, and store in a cool, dark place in peat moss or vermiculite until spring.
