Calla lily flowers grow from underground tubers that send out shoots in the spring. In USDA Plant Hardiness Zones 8 to 11, cut back the foliage in the fall and spread mulch over the tubers to keep them warm for the winter. In cold climates where the ground freezes hard in the winter, dig up the tubers and keep them inside to replant in the spring. In wet, humid conditions, calla lilies retain their foliage and flowers all year. Plant calla lilies in damp soil and keep them well watered through the growing season.
Plant calla lily tubers outside in the spring when the daytime temperature is above 65 degrees F. Dig holes 2 to 3 inches deep and place one tuber in each hole. Cover the tuber with soil and add water until the earth is damp to a depth of 3 inches all around the tubers.
Water calla lilies frequently to keep the soil around the roots continuously damp. This plant grows best in full sun, but it will tolerate partial shade.
Fertilize once a month using a balanced 10-10-10 fertilizer. Check the package to determine the right dilution and application method.
Cut flowers to bring inside at the base of the flower stalk. Use large sharp shears to make a clean cut through the fleshy stalk without damaging it. Make the cut at a 45-degree angle.