How to Grow Calla Lilies Indoors

Flowers as elegantly streamlined as italic script make calla lilies (Zantedeschia spp.) striking complements to the most casual or sophisticated interior decorating schemes. With proper growing conditions, the jewel-toned goblets last for weeks. A single caveat before welcoming callas into your home: From their blooms to their roots, the plants are loaded with highly toxic calcium oxalate crystals. Display them where they won't endanger children or pets.

Although callas are garden perennials in U.S. Department of Agriculture plant hardiness zones 8 through 10, depending on variety, those commonlyn grow indoors are hybrids (Zantedeschia x hybrida). They're hardy only in USDA zones 9 through 10.

Calla lilies need good drainage. Plant them in commercial, high-quality, peat-based potting mix and use deep pots with drainage holes. A 6-inch pot is large enough for one lily; an 8-inch one has room for two or three evenly spaced plants.

Plant the rhizomes, or bulbs, smooth side down in pots of pre-moistened potting mix at a depth at least twice their thickness. Water until liquid runs from the base of the container and let the pot drain completely.

Set the container in a spot with temperatures in the 60- to 85-degree Fahrenheit range and at least six hours of bright, indirect light each day. Water enough to keep the growing medium evenly moist while waiting for the rhizomes to sprout.

Callas dislike hot or cold drafts. Place them away from heating or air-conditioning vents.

For maximum flowering, keep the plants between 70 and 85 F during summer and fall and 60 and 75 F in winter and spring.

Water actively growing callas as needed to keep the growing medium moist without letting it become soggy. Excessive watering may cause stem and leaf yellowing from rotting rhizomes.

Before watering, test the medium a finger into its top 1 inch. If it's dry, water until fluid flows from the drainage holes, soaking the entire root system. Wait no more than one hour before emptying the water collection saucer.

From the time they sprout until they finish flowering, fertilize calla lilies every three weeks with a low-nitrogen, high-phosphorous liquid plant food. Look for one with the second of the N-P-K numbers on its label greater than the first, and apply it at one-half the label's recommended strength.

Replace a regular watering session with the fertilizer. Pour the solution evenly over the growing medium until it flows from the drainage holes.

One manufacturer recommends applying a solution of 1 to 3 tablespoons of its 0-10-10 liquid plant food diluted in 1 gallon of water to indoor plants every three weeks. For callas, you'd reduce it to between 1/2 and 1 1/2 tablespoons.

Different strengths of fertilizers require different application rates. Always stick with the rates recommended by the brand you choose.

Stop fertilizing when the flowers have bloomed so plants can prepare for their natural dormancy.

When the callas stop blooming and their foliage becomes brown, they're entering a rest period called dormancy. Prune the leaves back to the medium and store the pots in a cool, dark dry location with a temperature between 32 and 50 F. After two to three months, start watering and gradually return the pots to warmer temperatures and brighter light. Resume a regular fertilizer schedule when the new leaves emerge.

To avoid spreading disease, remove dead foliage with clean, sharp pruning shears disinfected in rubbing alcohol between cuts.

Between watering sessions, let the medium dry just a little more than you would during the growing season.