Zantedeschia fall into two main types: hardier outdoor forms, often called arum lilies, with striking white flowers; and the more tender forms, typically with white-spotted leaves and pretty flowers in yellow, orange, pink or dark purple. These are often called calla lilies.
The hardy forms of zantedeschia are Zantedeschia aethiopica and Z. pentlandii and their cultivars, also called arum lilies.
Arum lilies thrive in moist soil in full sun to partial shade. Choose a sheltered position and add some well-rotted organic matter before planting.
Water freely throughout the summer, and feed fortnightly with a balanced liquid fertiliser. Mulch annually in autumn with well rotted garden compost or manure.
Z. aethiopica can be grown as a marginal plant in water up to 30cm (12in) deep. Use aquatic compost and a 30cm (12in) deep planting basket.
Tender forms (calla lilies)
The tender forms of zantedeschia are mainly cultivars of Z. elliotiana and Z. rehmannii (also called Elliottiana hybrids and Rehmannii hybrids), but may also include Z. albomaculata and Z. jucunda. These are often referred to as calla lilies.
These tender varieties can be displayed either as houseplants or seasonal outdoor bedding displays. They will flower in summer.
For early flowering plants at Easter, plant the rhizomes in December. Keep in a light, cool place at a temperature of 16°C (61°F) by night and 18°C (65°F) during the day. Feed fortnightly with a high-nitrogen fertiliser when in active growth but withhold feed during flowering. A high potassium feed such as a tomato fertiliser can be given once a week after flowering.
Both these types of zantedeschia can be grown in containers. When planting, use a loam-based compost such as John Innes No. 2 and plant the rhizomes (underground stems) just showing at the surface of a container with the eyes of the rhizome uppermost.
Water freely through the summer and feed with a balanced liquid fertiliser every two weeks until the flowers have faded.
Z. aethiopica and cultivars: In all but the mildest regions, the foliage will be blackened by frost and should be cut away. Protect the overwintering crowns by covering with straw or bracken anchored with pegged down chicken wire.
When calla lilies (Z. elliotiana and Z. rehmannii, Z. albomaculata and Z. jucunda) are used outdoors for summer colour, you will need to lift the rhizomes before the first frosts and store them over winter before replanting them next spring when the risk of frost is passed. Store them in trays of compost in a cool, dark, frost-free place such as a garage or shed. Alternatively, overwinter at a minimum temperature of 10°C (50°F) indoors or in a warm greenhouse or conservatory. Ensure they are not overwatered - the cooler the temperature, the less water will be required.
Propagate by division, in spring. Small rhizomes that have been overwintered in pots under cover can literally be cut up into sections, each with a visible bud.
Large overwintered clumps in the garden can be divided in the same way as other perennials, by lifting the plant before there is much top growth, and chopping through the roots with a spade and dividing into smaller sections.
Plants can be grown from seed in spring, sowing one seed per 8cm (3in) pot and maintaining a temperature of 20°C (70°C). Germination should take place after a few weeks, but plants will not flower for two or three years.