Make sure the container you choose for planting calla lilies has drainage holes. Individual rhizomess fit well in 6-inch pots. For larger containers, space each plant 3 inches apart and 3 inches away from the edges of the container.
If you're reusing old containers, disinfect them before planting callas. Soak both plastic and ceramic pots in a mixture of 1 part bleach and 9 parts water for at least 10 minutes. Add a little dish detergent, and then scrub mineral deposits and other debris out of the pots. For plastic, use a scouring pad. For ceramic, steel wool or a wire-bristle brush work well. Rinse pots with clear water before filling them with soil.
Soil for Callas
Choose a well-drained, soilless potting mix when planting calla lilies. While callas prefer moist soil conditions, you don't want the soil to become waterlogged. Callas do best in rich, organic soil, so choose a mix that contains organic matter like pine bark compost or peat moss. Fill the container to within 3 to 4 inches of the top edge, and water the soil to moisten and settle it before planting the calla rhizomes.
Set calla rhizomes on top of the potting mix in a partially filled container, and then fill it in with more soil so the rhizomes are planted 1 to 3 inches deep, with 1 inch between the top of the soil and the edge of the pot. Make sure there is at least 1 inch of soil covering each rhizome.
If you're growing callas as houseplants, start them any time in late winter. For outdoor growing, plant calla rhizomes in mid- to late spring after temperatures reliably stay above 30 degrees Fahrenheit. Set the containers in full sun or partial shade. Bright, filtered sunlight is best for producing quality flowers and keeping the leaves from burning in the sun.
After planting calla rhizomes, keep the soil just barely damp until the first shoots appear. Once the plants start growing, increase watering to keep the soil evenly moist but not soggy. Don't let the plants dry out; too much water is better than not enough for calla lilies.
If your potting mix contains fertilizer, don't add additional nutrients for the first two to three weeks after planting. After that, calla lilies benefit from regular fertilization during the growing season. If you use a liquid fertilizer, mix it according to label directions and apply as a normal watering every two weeks. An all-purpose fertilizer with an N-P-K ratio of 24-8-16 diluted at a rate of 1/2 teaspoon per gallon of water works well.