Calla lilies (Zantedeschia spp.) are a smart choice for beds and borders. The calla lily flowers are actually spathes or petallike leaves that surround the tiny true flowers. Species include white calla lily (Zantedeschia aethiopica), golden calla (Zantedeschia elliottiana) and pink arum or calla lily (Zantedeschia rehmannii), all of which grow in U.S. Department of Agriculture plant hardiness zones 8 through 10.
Calla lilies can be used two ways in mixed garden beds and borders. They can be planted in the ground in spring after all danger of frost has passed, or grown in containers and paced in garden beds after spring flowers have faded. They pair well with other plants that like the same warm, sunny conditions. Interplanting with summer bloomers like canna (Canna spp.), which grow in USDA zones 7 through 10 and colorful tropical perennials like lantana (Lantana camara), which grows in USDA zones 10 to 11, adds up to a colorful, free-blooming border.
Wet borders -- those bounding a pond or water feature work well for white calla varieties like white and green-flowered "Green Goddess" (Zantedeschia aethiopica "Green Goddess") and shining white "Crowborough" (Zantedeschia aethiopica "Crowborough"). Emphasize the architectural character of the callas by adding them to borders that include varieties of feathery astilbe, like the white flowered "Deutschland" (Astilbe japonica "Deutschland"), which grows in USDA zones 4 through 9. Interplant both species with earlier blooming iris varieties such as variegated yellow flag (Iris pseudacorus "Variegata"), which grows in USDA zones 5 through 9.
If soil is problematic or non-existent, as on a porch or terrace, grow callas in containers and group them with other container plantings for a border effect. Shorter varieties, like the hybrid "Rubylite Pink Ice" (Zantedeschia "Rubylite Pink Ice"), which grows in USDA zones 9 to 10 and features soft pink flowers, works especially well in pots. Pair containers of bright yellow golden calla with tropical foliage plants like multicolored croton (Codiaeum variegatum var. "Pictum"), which grows in USDA zones 11 through 12. Callas can be grown as annuals outside of their hardiness ranges, or brought indoors for winter.
Calla lilies can be grown from rhizomes or you can buy potted plants. Plant rhizomes about 4 inches deep when weather warms in the spring. Uniformly moist soil is essential to callas and they must have supplemental moisture during dry spells if they are grown in standard garden borders. The plants grow best in full sun to light shade. White callas can also be planted by streams or directly into the muddy pond or stream bed, if the water is less than 12 inches deep. To overwinter, pot up plants in early fall. Place them in a brightly lit indoor space.
Take care when planting any calla lily around children or pets. Sap in the stems may cause skin irritation. All parts of the plants, including flowers, stems and rhizomes, can cause stomach problems if they are eaten. White calla lilies are considered invasive in some parts of the U.S.