Calla lilies are tender perennials that grow from bulbs to bloom in the spring. They are very sensitive to cold and are hardy in USDA Zones 9 through 11. Thriving in filtered sunlight or partial shade and very moist soil, they have an upright growth habit and both the flowers as well as the foliage are decorative. Beyond their natural hardiness range, they are grown as annuals, dug up in the fall and stored over the winter before being replanted in spring after the last frost has passed.
Dig up your calla lily bulbs carefully in the fall in climates where they do not overwinter. Do this after the first frost has come and the foliage is just starting to fade. Excavate around the bulb with a hand trowel and lift it from the soil. Cut off the top foliage with clean sharp secateurs and dust the soil from the bulb and roots.
Prepare a shallow winter storage container by filling it with peat moss or clean dry sand three-quarters of the way full. Set the bulbs down into the prepared medium so that the bulbs are not touching one another and are not laid more than two layers deep. Cover over the bulbs with 1 inch of storage medium but do not seal the container as airflow will prevent rot.
Store the bulbs in a dry and cool, but frost-free, location for their winter rest interval. Inspect them once a month at least to check for rot or excess moisture. If one of your bulbs has rotted, scoop the bulb and the immediate surrounding storage medium and discard in the trash.