To grow Callas outdoors: Plant after danger of frost has passed in full sun or partial shade (partial shade is required in the South and warm inland areas of the West unless the soil is constantly wet) and rich moist soil. Rhizomes should be planted horizontally, with the growing points facing up. Grow in containers (3 per 12-inch pot) or in the garden. Rhizomes in containers should be planted just 3 inches deep. Hardy to Zone 9 (20°F), but an ample layer of mulch applied in fall can get plants through winter in Zone 8 (10°F) and even Zone 7 (0°). In colder climates, dig the rhizomes when frost threatens in fall and store them indoors in dry peat moss or sand at a temperature between 60° and 75°. Calla Lilies grown in a container can be left in the container over winter. Bring the container indoors in fall and withhold water completely until you want to start growth again in spring.