Calla lilies, which are not cold-hardy, are grown as potted plants in many northern locations. The flowers can be planted outside if the right conditions and care are present. It’s common to purchase calla lily plants which are already potted and started, then transfer them outdoors to a garden environment. Alternatively, gardeners may start callas from bulbs and watch them sprout as weather warms.
Find a spot in the garden offering evenly moist soil. Calla lilies may be planted in partial shade or full sunlight, and while they will grow in wet soils, they will not thrive in very shady or dry soils. Warm-loving calla lilies will not survive in temperatures below 50 degrees Fahrenheit, and may be grown outside year-round in U.S. Department of Agriculture hardiness zones 8 through 10. Gardeners living farther north may plant calla lily bulbs in 5- or 6-inch pots, which can be moved indoors as temperatures begin to drop.
New calla lily flowers are started from rhizomes, which look like small flower bulbs. Each one should be planted 1 inch into the soil and placed 2 feet apart. Gardeners in USDA hardiness zones 9 through 11 may plant calla lilies outside in the late fall. Outside of these zones, plant the rhizomes in pots indoors in the late winter, and carry them to the garden for transplant in the early spring.
Unless grown in ideal temperatures (50 degrees Fahrenheit and above), calla lilies will not survive the winter. At the end of the summer, dig up the rhizomes you planted so they may be stored over the cold season. Keep bulbs cool and dry until late winter, when they may be re-planted so the cycle can begin again. Rhizomes should be stored in a box filled with sand or peat moss.
Calla lilies require regular maintenance to stay healthy and continue to thrive. After the blooms begin to wilt and fade, they must be deadheaded. The technique requires snipping off the blossom just above the first leaf joint. Fertilize the flowers in spring with a slow-release nitrogen blend when the foliage begins to emerge. Pull up any weeds that appear around the calla lily plants to ensure that the flowers receive plenty of nutrients.