Calla lily

Identification and origin

Zantedeschia aethiopica belongs to the family Araceae; despite its common name, it is not a true lily. It is native to southern Africa: the Cape Provinces, KwaZulu-Natal, the Free State, the Northern Provinces, Lesotho, and Eswatini. It grows in a wide range of habitats, from coastal marshes to mountain grasslands, often along stream banks and pond margins. Introduced to many parts of the world, it has sometimes naturalized to the point of becoming weedy.

It is a perennial that grows from a fleshy rhizome. Its leaves, held on long, thick stalks, are glossy dark green, heart- to arrow-shaped with wavy edges, and up to 16 in long. On bare stalks appears the typical inflorescence of the arum family: a white, funnel-shaped spathe tapering to a point, 8–10 in long, wraps around a yellow spadix 3–4 in long that carries the tiny, lightly fragrant flowers. The fruits are yellow-orange berries about 0 in across, clustered on the spadix. A mature clump reaches 2–3 ft tall and 18 in – 2 ft wide. Where water is plentiful and winters are mild, the foliage stays evergreen; cold or a long dry spell makes it die back until the next season.

The genus honors the Italian botanist Giovanni Zantedeschi; aethiopica means “African.” It is a highly prized cut flower. Cultivars include ‘Crowborough’, more cold tolerant, ‘Green Goddess’, with green-streaked spathes, and ‘White Sail’, with very large spathes. The colored callas sold in pots belong to other, more tender species.

Light

Calla lily grows in full sun or part shade and blooms best in full sun. In hot climates, part shade keeps the leaves and spathes from scorching, at the cost of somewhat fewer flowers. A plant brought indoors for winter belongs near a very bright window, out of harsh sun.

Watering

This is a plant of moist ground that even tolerates wet feet. Throughout the growing season the soil should never dry out: water as soon as the surface loses its moisture, and keep a close eye on container plants, which dry out much faster than plants in the ground.

At the edge of a pond, it grows in water up to 12 in deep. In winter, or whenever it goes dormant, cut back sharply on water: a waterlogged rhizome in a plant that is not growing will eventually rot.

Potting mix

It needs soil rich in organic matter, amended with leaf mold, well-rotted manure, and humus, that holds moisture. It adapts to clay or loam and to acidic, neutral, or alkaline soil. In containers, use a loam-based, peat-free mix. For pond culture, plant it in an aquatic basket no more than 12 in wide, filled with aquatic soil or heavy loam and topped with gravel so the soil does not wash out.

In fertile soil it needs no fertilizer. In poor soil or in containers, apply a balanced liquid fertilizer every two weeks while it blooms.

Temperature

This is the hardiest species in its genus: in the ground it tolerates frosts of around 14–23 °F and overwinters outdoors in USDA zones 8a to 10b, even zone 7 with protection. Young plants remain vulnerable, even in mild climates. Before winter, cover the crown with mulch at least 6 in deep in mild regions and about 12 in elsewhere, or with straw. Planted in a pond, the rhizome can survive if the water does not freeze to the bottom.

In containers, the roots are far more exposed: move the pot to a sheltered spot against a wall and wrap it in several layers of frost cloth, or bring it into a frost-free space. In cold regions you can also dig the rhizomes in fall and store them in a slightly damp medium such as peat, or pot them up to overwinter as a houseplant.

Repotting

Repot or divide overcrowded clumps in early spring, before growth resumes. Replant at the same level as before, no deeper. In the garden, plant rhizomes in spring once the danger of frost has passed, 3–4 in deep and 12–18 in apart; clumps fill out quickly, so leave room. A single rhizome can be started in a pot just larger than itself, with very little water until shoots appear.

Pruning

No pruning is needed. After blooming, remove each spent flower stalk by pulling it from the base. Also remove foliage blackened by frost.

Propagation

Division is the easiest method. In early spring before growth starts, or in late summer to early fall after flowering, lift the whole clump and break it into pieces that each carry a few growing buds, or “eyes.” Let the cuts dry and callus for a day or two before replanting.

Seed can be sown in spring at about 70 °F: germination takes a few weeks. Sow sparingly, since the fleshy roots need room. Expect two to three years before the first flowers.

Common problems

• Rhizome rot: too much water during dormancy, or cold, soggy soil; fungal and bacterial rots can also affect the plant.
• Scorched leaves and spathes: sun too strong in a hot climate.
• Blackened foliage: frost; cut away the damaged parts.
• Virus: the species can also be affected by a virus.
• Pests: aphids and thrips; under glass or indoors, spider mites and whiteflies; outdoors, Japanese beetles, where present, feed on leaves and flowers.

The same symptom can have several causes: consider watering, season, temperature, and the condition of the rhizome before drawing conclusions.

Toxicity

All parts of the plant are toxic to dogs, cats, and horses, as well as to people. They contain insoluble calcium oxalate crystals that, when chewed, cause irritation and a burning sensation in the mouth, tongue, and lips, excessive drooling, vomiting, stomach pain, and difficulty swallowing. The sap can also irritate skin and eyes: wear gloves when handling it. Keep the plant out of reach of children and pets, and if it is eaten, contact a veterinarian or a poison control center.