A family of part-hardy and tender perennials loved for their flamboyant colourful upright flowers (spathes). Most are grown as greenhouse or houseplants but a few varieties will actually grow quite well outdoors in mild regions.
Family: Araceae (arum family)
Botanical Name: Zantedeschia (zan-teh-DIS-kee-ah)
Common Names: Arum lily, calla lily
Foliage: Tall wide, upright, semi-evergreen leaves.
Flowers: Tiny flowers that form a dense spike-like spadix, surrounded by a showy, hood-like spathe.
Flowering Period: Spring to early summer.
Soil: Moist, poorly-drained soil (clay or loam). Acid, alkaline or neutral pH.
Conditions: Full sun or part shade. Plant hardy varieties in a south or west facing aspect, in a sheltered location.
Habit: Upright, clump forming.
Type: Tuberous perennial.
Origin: Southern Africa.
Hardiness: Tender to part-hardy, depending on variety.
Toxicity: Can cause severe discomfort if ingested. The sap can irritate skin. Wear gloves and wash hands after handling.
In mild areas hardy forms can be planted outdoors in a sheltered border. Site in sun or partial shade in a moisture retentive soil. Ideal for boggy ground or near a pond.
In mild winters hardy arums can be evergreen. However the leaves can be frost damaged during winter, if this happens trim them back after the last frosts and new shoots should appear from the ground.
For tender varieties, water freely during growing period. They can be moved outside in summer and brought back indoors in the autumn. Once flowering has finished, dead head and reduce watering until dry, then store in a frost free area until late winter.
Water liberally during the growing season and occasionally apply a liquid fertiliser during the flowering season.
For outdoor varieties remove the dead and flowers and any damaged leaves in the autumn and apply a winter mulch to protect the underground tubers.
Re-pot houseplants plants every autumn in rich, light sandy loam.
Susceptible to Aphids and thrips. Can be affected by cucumber mosaic virus and tomato-spotted wilt virus.
Propagate by division in spring or increase by separating offsets in winter.
Hardy arum rhizomes can sometimes be purchased in late winter, ready for planting outside in late spring. Although are usually available as pot grown speciments in spring/summer. The flowers of hardy arums are usually white and derived from the species Z. aethiopica and Z. pentlandii.
Tender forms, usually referred to as Calla lilies, are available in a wide range of bright colours.
Zantedeschia albomaculata (white spotted arum) a tender form with ivory white spathes and a yellow spadix. Semi-erect, wavy, mid-green leaves flecked with small white spots. Height to 18in (40cm).
Zantedeschia aethiopica (arum lily) a part-hardy form that will survive outdoors in mild areas. Mainly white spathes with a central erect yellow spadix. Large mid-green leaves. Height to 3ft (90cm), spread 18in (45cm).
Zantedeschia elliottiana (golden arum lily, golden calla) a tender form with green leaves spotted with white. Bright yellow spathes and spadixes in summer. Height and spread to 24in (60cm).
Zantedeschia jucunda (yellow arum) bears pale yellow to a very dark yellow spathes. Rarely found in general cultivation, although seeds are available from online dealers.
Zantedeschia pentlandii a part-hardy form that may survive outdoors in mild areas. The spathes are white or yellow.
Zantedeschia rehmannii (pink arum lily, pink calla) a tender form with pink to red spathes and yellow spadixes. Height and spread to 12in (30cm).
Zantedeschia hybrids a wide range of colourful, summer-flowering cultivars are available. Often unnamed and frost tender, they are usually crosses of Z. elliotiana and Z. rehmannii but may also include Z. albomaculata and Z. jucunda. They can be grown as either houseplants or seasonal outdoor bedding.