Calla lilies, scientifically known as Zantedeschia, are popular ornamental plants prized for their elegant, trumpet-shaped spathes and striking foliage. Successful growth and vibrant flowering depend heavily on planting the rhizomes at the correct time, which is dictated by the environment. Understanding the optimal planting window is the first step toward a thriving plant. The timing ensures the plant is not exposed to damaging temperatures and can begin its growth cycle efficiently.
Outdoor Planting Timing Based on Climate
Planting Zantedeschia rhizomes directly into the garden should only occur in the spring after the danger of the last frost has passed. This typically falls in late spring or early summer for most temperate regions. The plant is a tender perennial and cannot tolerate freezing temperatures, which would destroy the rhizome.
The most precise indicator for planting is the soil temperature, which should ideally be around 65°F (18°C) or warmer. Cooler temperatures, even above freezing, can cause the rhizomes to temporarily stop growing, delaying the emergence of the foliage and subsequent blooms. In warmer climates (USDA Hardiness Zones 8 through 10), calla lilies can often be left in the ground year-round or planted earlier in the spring.
Gardeners in cooler zones (3 to 7) may start the rhizomes indoors in pots a month or two before the final frost date to get a head start. This process allows the plant to establish roots in a controlled environment before being transplanted outdoors once the soil has warmed sufficiently. Lifting them for storage is necessary in these colder areas because the ground freezes over winter.
Year-Round Planting for Indoor Growth
Growing calla lilies as houseplants removes the constraints of external frost dates, allowing the rhizomes to be planted at any time of the year. The indoor environment offers consistent conditions necessary for continuous growth. The temperature range of 65°F to 75°F (18°C to 24°C) is preferred for active growth, easily maintained within a home.
For specific indoor bloom timing, particularly for holidays or events, the rhizomes can be “forced” to flower by manipulating their dormancy cycle. The plant must be given a resting period of two to three months in a cool, dark place, ideally around 50°F (10°C), without water. After this forced dormancy, repotting the rhizome in fresh soil and providing bright, indirect light will initiate a new growth cycle leading to blooms within two to three months.
Mechanical Steps for Successful Planting
Once the correct timing has been determined, the physical act of planting the rhizome requires attention to detail to ensure proper establishment. The rhizome must be planted with the correct orientation. Locate the “eyes” or growing points and place the rhizome in the soil with these sprouts facing upward.
The planting depth should be shallow, generally only 2 to 3 inches deep beneath the soil surface. This shallow depth allows the emerging shoots to reach the surface easily while keeping the rhizome protected. Calla lilies thrive in a rich, well-draining soil that contains ample organic matter, preventing the rhizomes from rotting in soggy conditions.
Positioning the plant in a location that receives full sun to partial shade is also important. While full sun encourages the biggest blooms, afternoon shade is beneficial in extremely hot climates to prevent leaf scorch. After planting, water the area thoroughly to settle the soil around the rhizome, but avoid heavy watering until the first leaves emerge to prevent rot.
Post-Bloom Care and Preparing for Dormancy
The annual growth cycle of the calla lily concludes with a period of dormancy, which is necessary for the rhizome to rest and store energy for the following season. After the plant has finished blooming, usually in late summer or early fall, the foliage will naturally begin to yellow and die back. This color change signals that the plant is entering its resting phase.
During this transition, gradually reduce the amount of water provided to the plant, allowing the soil to dry out significantly. Do not cut the yellowing leaves off prematurely, as they are still photosynthesizing and transferring energy back to the rhizome. Once the foliage has completely browned, the plant has officially entered dormancy.
In climates where the ground freezes (colder than Zone 8), the rhizomes must be lifted and stored for the winter before the first hard frost occurs. The foliage should be cut back, and the rhizomes gently dug up and cleaned of excess soil. They must be allowed to cure in a warm, dry place for a few days. Storing the cured rhizomes in a cool, dark location, such as a paper bag filled with peat moss, will keep them viable until the optimal planting time returns in the spring.