The Calla Lily (Zantedeschia) is a popular ornamental plant known for its distinctive, trumpet-shaped flowers (spathes) and lush, often speckled foliage. Whether this plant can be successfully grown outside depends almost entirely on your local climate conditions. Understanding the plant’s specific needs for warmth and dormancy is the first step toward successful outdoor cultivation.
Determining Climate Suitability
Calla Lilies are tender perennials native to Southern Africa, meaning their ability to survive winter outdoors is strictly limited by temperature. Gardeners in USDA Hardiness Zones 8 through 10 can treat the Calla Lily as a true perennial, allowing the rhizomes to remain in the ground year-round. In these warm regions, the plant enters a natural dormancy period but reliably re-emerges each spring without intervention.
Outside of these mild zones (Zones 3 through 7), the plant is not winter-hardy and must be treated differently. Gardeners in cooler climates must grow Calla Lilies as seasonal annuals or lift and store the rhizomes indoors before the first hard frost. This means the plant provides summer color but cannot survive the freezing temperatures necessary for overwintering in the soil.
Planting Procedures and Timing
The Calla Lily grows from a thick, fleshy underground stem known as a rhizome, and timing its planting is crucial for summer blooms. Rhizomes should be planted in the spring after the danger of the last frost has passed and the soil has warmed. Ideal soil temperatures should reach at least 55°F to 65°F before planting to encourage growth and prevent rot.
The chosen location should offer rich, well-draining soil that is slightly acidic to neutral, ideally with a pH between 5.6 and 7.0. While Calla Lilies appreciate sunlight, the intensity of that light should be adjusted based on your climate. In northern or cooler regions, full sun encourages the best blooms, but in hot, southern climates, partial shade is necessary to prevent the foliage from scorching during intense afternoon heat.
To plant the rhizome, dig a hole that is about 2 to 4 inches deep, ensuring the soil is loose and rich in organic matter. The rhizome should be placed horizontally with the growing points, often called “eyes,” facing upwards toward the soil surface. After covering the rhizome with soil, water the area thoroughly to settle the soil around the developing roots.
Essential Summer Care
Once the Calla Lily is established and actively growing, consistent moisture is necessary for flowering performance. The soil should be kept evenly moist throughout the entire growing season, particularly during dry spells. Ensure the planting site drains well, as soggy conditions quickly lead to rhizome rot and fungal diseases.
Regular feeding provides the energy to sustain continuous bloom production. During the active growth period of spring and early summer, apply a balanced liquid fertilizer (such as a 10-10-10 or 20-20-20 formula) every four to six weeks. Stop fertilizing once flowering begins to slow down to allow the plant to prepare for dormancy.
Removing spent blooms, known as deadheading, encourages the plant to produce new flowers rather than setting seed. Monitor for common pests:
- Aphids
- Slugs
- Spider mites
These can be managed with insecticidal soap or physical removal. Bacterial soft rot, signaled by yellowing leaves and mushy stems, is the most serious disease threat and results from excessive soil moisture.
Preparing for Winter Dormancy
The necessary preparation for winter depends on whether the Calla Lily is a perennial or must be treated as a seasonal annual. In Zones 8-10, minimal action is required; simply allow the foliage to die back naturally and cut the remaining leaves down to the ground level. Applying a layer of mulch over the planting site can offer protection during the cooler winter months.
For gardeners in colder climates, the rhizomes must be lifted before the first hard frost to prevent freezing damage. Wait until the foliage has yellowed or died back, then carefully dig up the rhizomes, gently brushing off excess soil. The rhizomes must then be cured by placing them in a warm, dry, and well-ventilated location for four to seven days, typically at a temperature between 65°F and 75°F.
Curing allows the outer layer of the rhizome to toughen, which protects it during storage. Once cured, the rhizomes should be stored in a dark, cool place where the temperature consistently remains between 50°F and 60°F. Packing them in a medium like dry peat moss, sawdust, or loosely in a paper bag provides insulation and prevents moisture buildup, ensuring they remain viable for replanting the following spring.