Calla Lilies (Zantedeschia) are highly sought-after plants for gardens and floral arrangements due to their striking, trumpet-shaped spathes and lush foliage. They can be planted outside, but successful outdoor cultivation depends entirely on the local climate, as their survival through colder months is tied directly to hardiness.
Understanding Calla Lily Hardiness
Calla Lilies are tender, tropical perennials native to southern Africa, growing from fleshy, underground structures called rhizomes. In their native environment, they are perennial, but in many parts of the world, they are treated as seasonal annuals due to their intolerance for cold temperatures.
The ability of a Calla Lily to survive the winter in the ground is determined by the USDA Plant Hardiness Zones. Most Calla Lily varieties are reliably hardy and can be left in the ground year-round only in Zones 8 through 11. Zone 8 is considered the coolest region where they might perennialize, provided they have adequate winter protection.
If you live in Zones 7 or lower, the rhizomes cannot withstand freezing temperatures and must be dug up and stored indoors for the winter. In these cooler climates, the plant is typically grown as a summer-blooming annual. The distinction is simple: warm zones allow for year-round residency, while cold zones require temporary relocation of the rhizomes for winter survival.
Optimal Planting Conditions and Timing
Planting should occur in the spring after the danger of the last frost has passed. Wait until the soil temperature warms up to at least 55°F to 65°F, which encourages prompt growth. Planting too early in cold, wet soil can lead to the rhizomes rotting before they sprout.
Select a planting location that offers rich, well-drained soil, as soggy conditions are detrimental to the rhizomes. While they appreciate consistent moisture, the soil must not retain standing water. Calla Lilies perform best in full sun to partial shade, requiring six to eight hours of light daily.
Plant the rhizomes shallowly, typically three to four inches deep, with the growing points (“eyes”) facing upward. Space them about 12 to 18 inches apart to allow room for growth and multiplication. After planting, water the area thoroughly to settle the soil, but avoid overwatering until the first leaves emerge.
Ongoing Care and Winterizing
During the summer growing season, Calla Lilies require consistent moisture, especially in warmer climates; do not allow the soil to dry out completely. They benefit from regular feeding every few weeks with a balanced liquid fertilizer until the blooms fade. Avoid high-nitrogen fertilizers, which promote leafy growth at the expense of flower development.
Winterizing in Warm Zones (8 and Higher)
As the growing season ends in the fall, the plant enters dormancy, with the foliage turning yellow and dying back. To prepare for winter in warm zones, stop watering and cut the dead foliage down to the ground. Applying a thick layer of organic mulch over the planting area provides extra insulation for the resting rhizomes.
Winterizing in Cold Zones (7 and Lower)
In colder regions, the rhizomes must be lifted after the first light frost kills the foliage. Carefully dig them up, brush off the excess soil, and allow them to “cure” in a warm, dry, shady spot for one to two weeks. This curing process toughens the outer skin and helps prevent rot during storage.
Once cured, store the rhizomes in a cool, dry, and dark location (50°F to 60°F), such as a basement or garage. Place them in a ventilated container, like a paper bag or cardboard box, covered with a dry medium such as peat moss, vermiculite, or sawdust. Check the stored rhizomes occasionally to ensure they are not shriveling or rotting.