Arum Lily (Zantedeschia aethiopica)

The calla lily is a well-known ornamental plant with several cultivars receiving the Royal Horticultural Society’s Award of Garden Merit. The most calla lily cultivars include ‘Crowborough’, ‘Green Goddess’, ‘Pink Mist’, and ‘Red Desire’. They are popular as a cut flower or a rhizomatous herb in warm gardens.

I. Appearance and Characteristics 

Zantedeschia aethiopica, commonly known as calla lily and arum lily, is a species of flowering plant in the family Araceae, native to southern Africa in Lesotho, South Africa, and Eswatini.

Until 2011, Zantedeschia aethiopica was the national flower of the island nation of Saint Helena, where it grows widely, but is considered an invasive plant. Further, it is an important symbol of Irish republicanism and nationalism since 1926, because it is used to commemorate the dead of Easter 1916 and onward.

Zantedeschia aethiopica is a rhizomatous herbaceous perennial plant, evergreen where rainfall and temperatures are adequate, deciduous where there is a dry season. Its preferred habitat is in streams and ponds or on the banks. It grows to 0.6–1 m (2.0–3.3 ft) tall, with large clumps of broad, arrow shaped dark green leaves up to 45 cm (18 in) long. The inflorescences are large and are produced in spring, summer and autumn, with a pure white spathe up to 25 cm (9.8 in) and a yellow spadix up to 90 mm (3+1⁄2 in) long. The spadix produces a faint, sweet fragrance.

Zantedeschia aethiopica contains calcium oxalate, and ingestion of the raw plant may cause a severe burning sensation and swelling of lips, tongue, and throat; stomach pain and diarrhea may occur.

The reproduction of Z. aethiopica involves seeds dispersal by birds and vegetative propagation through rhizomes that can spread when soil or garden cuttings are moved.

II. How to Grow and Care

Sunlight

True to their tropical nature, calla lilies thrive in a warm environment, including plenty of light. If you have hot and humid summer weather, your calla lilies might do better in a spot with partial shade. If you have a more temperate summer climate, your calla lilies can handle full sunlight.

Temperature and Humidity

Calla lilies like a fairly warm environment and temperatures between 60 and 80 degrees Fahrenheit. They also enjoy a decent amount of humidity and moisture, so humid summers keep the flowers blooming just fine. When temperatures drop below 50 degrees Fahrenheit, the plants enter dormancy. Dig up your rhizomes for overwintering before freezing temperatures occur. Frost can kill the plant.

Watering

Once the rhizomes are established, you can water the plants once a week or more frequently if experiencing especially hot or drought-like conditions. Calla lily plants potted indoors will need constant moisture, as pots will dry out sooner than ground plantings.

Soil

A rich, moist, well-drained soil is best to keep calla lilies blooming. Calla lilies often do well growing alongside ponds and can happily tolerate a moist soil location. Although avoid allowing these plants to become waterlogged, as it can lead to root rot. To increase the nutritional density of your soil, amend it with organic matter before planting your flowers.

Fertilizing

Calla lilies need feeding upon planting and every spring at the beginning of the growing season to promote bountiful flowering. Most well-balanced fertilizers will work just fine. Avoid choosing a blend that is nitrogen-heavy; it can reduce the plant’s flowering.

Pruning

Calla lilies don’t require regular pruning, but you can pull off wilted flower parts. Removing parts of this plant will not kill it. Pinch stems just below the base of the flower with your fingertips or use sterilized pruning shears. If you live in zone 8 or warmer, when it dies back at the end of the growing season, cut it down to the soil level and dispose of any plant debris. In the spring, it will return. (It is recommended to wear gloves when working with this plant to avoid touching the sap.)

Propagation

Calla lilies can be propagated by dividing their rhizome or rooting structure or growing the plant from seeds. Calla lilies form into large clumps, and you can divide the clumps into separate plants. Plants grown from rhizomes will flower much sooner than seed-grown plants. Here’s how to divide a calla lily rhizome for propagation:

• If your calla lily is in the ground, you will need a shovel or pitchfork to pull up the rhizome. If you plan to keep the plant warm indoors, you’ll need potting soil and a clean pot.
• Use the shovel or pitchfork to cut a circle around the root to make it easier to pull up.
• Once you’ve pulled up the clumped root, brush off the dirt from the rhizome and place it in a shady, well-ventilated area for several days. Do not wet or water it.
• Once it has dried out, use a sharp knife to separate the rhizomes. They don’t have to separate exactly where they connect but make sure each piece of rhizome has at least one eye or roots growing from it.
• Replant the rhizome in a compost-enriched garden bed at least six inches from other plants or place it in a potting container with moist, well-draining soil. Or you can store the rhizomes over the winter.

Grow from Seed

It can take up to three years for a calla lily planted from seed to bloom. Calla lily seeds must be pre-grown, which can be done by spreading seeds out on a damp paper towel and covering them. Place the paper towel in a cool location, such as a basement or cellar. After a few days, check for growth. Discard any that do not show any signs of life.

Put the seed in a high-quality soilless medium in a well-draining pot. Keep the soil moist and watch for growth. Watch the plants for a couple of weeks and remove the weakest shoot from each pot. You only want one seedling per pot.

Potting and Repotting 

One indication that your calla lilies are ready for a bigger pot is when the roots start to look crowded. Root-bound calla lily plants will not thrive, so replant them if you notice an issue with their roots. Get a pot that is at least two or three inches deeper and wider than the old pot.

To repot calla lilies, carefully lift the flowers out of their smaller pot and gently place them into the larger one, taking care not to damage the delicate roots. Fill the new pot with soil up. Keep the soil moist consistently for a few days after repotting. Make sure the soil is not soggy or waterlogged.

Terracotta pots are a great option for this plant since the porous nature of the pot allows air and water to pass through its walls, promoting healthy plants by helping prevent overwatering. A downside to clay pots is soil dries out quicker, requiring more frequent watering.

Overwintering

If you live in a USDA hardiness zone cooler than 8, you can dig up and overwinter the rhizomes, or buy new rhizomes each growing season. Once you dig up a rhizome, gently brush off any remaining dirt. Do not wash or water the calla lily rhizomes since that can cause fungal root rot.

Cut off the foliage from the top of the rhizomes. Allow the rhizomes to dry in a warm, dry, well-ventilated place for four to seven days. This is important to calla lily care in winter because it allows the outer skin of the rhizome to toughen up or cure.

After the calla lily rhizomes have dried, place them in a paper bag or wrap them separately in newspaper. Store them in a cool, dry place: somewhere that stays around 50 degrees Fahrenheit. Usually, a garage or basement works well.

Pests and Diseases

Common Pests and Diseases

You may have to contend with several issues when growing calla lilies, most notably bacterial soft rot, which affects the rhizomes, and botrytis, which is a fungal disease that causes a filmy grey mold to grow over the plant’s petals, stems, and leaves.34 To reduce the risk of fungal diseases, don’t overwater the plants, and make sure to plant your calla lilies far enough apart so that they have ample air circulation.

Various pests can also be an issue for calla lilies, including insects like aphids, slugs, and spider mites.5 Treat the plants with a mild insecticidal soap or horticultural oil like neem oil to combat these issues.

Common Problems

It’s generally easy to grow calla lilies. Other than regular water, they do not need much care. However, if their growing needs aren’t met, they can suffer.

Brown Edges of Leaves

If you notice a brown edge on the leaves, it may be a sign that your fertilizer has too much nitrogen in it. If your plant grows rapidly and looks lush but has brown-edged leaves, a nitrogen-rich fertilizer can cause that. Your plant will likely not bloom either.

Yellowing Leaves, Wilting, or Stunted Growth

Calla lilies are water lovers. If they are not getting enough water, they may not bloom, will look stunted, and leaves will appear yellowed and wilted. Water calla lilies consistently to keep your plant’s foliage healthy and encourage flowering; stunted growth can also be caused by lack of sunlight.

Drooping Stems and Flowers

Plant droop can be caused by too little and too much watering. Also, too much nitrogen in fertilizer can lead to drooping stems and flowers. If it doesn’t have enough water, adding water will help it perk up.

III. Uses and Benefits 

Calla lily is quite attractive when clustered near ponds or in flower gardens. With its uniquely appealing appearance, multitude of colors, and easiness of growth, this is a plant that is very popularly planted along garden borders and in flower beds. This superstar lily can be complemented by the foliage of White sage or Hakone grass.