Native to the swamps of southern and eastern Africa, calla lilies (Zantedeschia spp.) need some direct sunlight to ensure flowers form. While the tuberous rhizome roots will grow and display the attractive green and white spotted leaves, shady conditions don’t encourage production of the trumpet-like blooms in late spring to midsummer.
Pink colored spathe of a calla blossom
Susan Bryant of Lakeside Callas of Dandridge, Tennessee warns that planting calla lilies in heavy shade inhibits flowering. Plant calla tubers, sometimes simply but incorrectly called bulbs, where they receive at least partial shade, two to five hours of direct sun each day. Calla lilies also grow well with more sunlight, even full day sun as long as the soil is fertile, cool and provides enough moisture.
The ideal soil for planting and growing calla lilies contains lots of humus or compost. A fertile loam soil has an excellent texture, but both sand and clay soils become more suitable for calla lilies with addition of organic matter. The soil needs to retain water, staying evenly moist or even soggy wet, such as part of a bog or edge of a pond. The more direct sunlight a calla receives, the moister the soil must remain. Otherwise, leaves scald and edges brown.
Calla lilies persist as perennials in U.S. Department of Agriculture plant hardiness zones 8 and warmer. Elsewhere, the winters are too cold and the tubers must be dug up and stored indoors. In the cooler summers and less intense sun rays across Canada and the northern United States, calla lilies prosper with as much sunlight daily. By contrast, in the hot-summered southern states, sunlight is more intense so a partial sun to partial shade situation is better, as it helps keep soil cooler and not need as frequent watering.
White calla lily, Zantedeschia aethiopica
Production greenhouses force calla lilies into bloom for sale as seasonal gift plants year-round. Indoors, calla lilies need as much sunlight as possible or very bright indirect light all day long. Without ample light, flowers don’t form. If grown as a houseplant, place calla lilies in a sunny room, solarium or conservatory and follow cultural needs to keep the plants healthy.