Adorning gardens with colorful, exotic-looking flowers, calla lilies (Zantedeschia aethiopica) are summer perennials thriving in U.S. Department of Agriculture plant hardiness zones 8 through 10. They are not true lilies despite the name. When frost damages the foliage, don’t fret. This is normal and signals that some immediate care is needed, especially in cool climates, so that the rhizomes from which callas grow do not become damaged. If you keep the rhizomes alive during the cool months after a frost, they’ll put forth new growth and flowers again the next year.
Cut the foliage to the ground after the frost kills it back. Leave the rhizomes in the garden in zones where callas are hardy. In USDA plant hardiness zone 8, cover the area with 2 inches of mulch, such as straw or leaves, in case winter is cooler than usual.
Remove calla lily rhizomes from the ground in USDA plant hardiness zones 7 and cooler by digging around the clump with a garden fork. Dig about 6 to 8 inches deep to ensure you get under the rhizomes, and lift.
Brush the soil off of the calla lily rhizomes, and set them out in the sun for three days. Bring them indoors into a dry area if frost is likely to occur during the nights.
Examine the rhizomes for rot, possibly caused by the cold temperatures. Cut the damaged areas off with a clean, sterile knife. Discard the damaged pieces and keep the healthy portions until spring, along with the other rhizomes.
Pack the rhizomes in peat moss in an open box or bag, and store in a cool, dry area that is above freezing, ideally between 45 and 55 degrees Fahrenheit. Keep them there until spring when the last frost passes, at which time you can replant them outdoors.