Arum lily

Arum lily: how do you recognise it?

Habit

Broad clump 60–90 cm tall and about 60 cm wide, with leaves and flower stems rising straight from the ground.

Leaves

Large, arrow- to heart-shaped, glossy dark green, on long, fleshy stalks. They stay in mild winters and die back in frost.

Flower

A funnel-shaped spathe 10–25 cm long around a yellow spadix, from June to August.

Colour

Pure white with a yellow spadix; in ‘Green Goddess’ green with a white throat.

Rhizome

Thick, fleshy rhizome that slowly spreads into a sizeable clump.

Flowering: June–August · Plants: April–May

Why grow it?

• Stately white flowers from June to August that stay beautiful for a long time on the plant and in a vase.
• Large, glossy leaves that give a border or pond edge a lush, exotic feel, even without flowers.
• One of the few plants for wet, heavy soil and even for shallow water at a pond edge.
• A classic cut flower: one plant gives several stems every summer.
• Little work: no pruning, just water, some feed and a winter blanket of mulch.

Arum lily: where does it grow best?

• Sun or partial shade; in full sun the soil must always stay moist.
• Rich, humus-rich soil: loam, clay or peat, acid, neutral or chalky.
• Moist to wet: at a pond edge, in a bog garden or in shallow water.
• A warm, sheltered spot, for example by a south-facing wall, helps it through the winter.
• Allow about 60 cm of space per plant.

Light

Sun and partial shade

Soil type

Loam, clay or peat

Acidity

Not fussy

Moisture

Normal or wet

Size

0.9 m tall, 0.6 m wide

Hardiness

Half hardy (to -10 °C): protect it in harsh winters

Goes well with

• Hosta: Large blue or yellow-green leaves beside the glossy arum lily leaves, in the same moist spot.
• Royal fern: A large fern for wet soil, with finer leaves as a contrast.
• Yellow flag iris: Yellow flowers at the pond edge in May–June, just before the arum lily flowers.
• Astilbe: Pink and red plumes in the same moist partial shade.
• Purple loosestrife: Purple spikes at the water’s edge in July–August that attract bees and butterflies.

Arum lily: when and how to plant it?

Plant in April–May.

1. Plant in April–May, once the soil has warmed up and hard frost is no longer likely.
2. Dig a roomy planting hole and mix in a few spadefuls of compost or well-rotted manure.
3. Set the rhizome 10 cm deep, with the growing points facing up, and space plants about 60 cm apart.
4. In a pond: plant in an aquatic basket filled with heavy garden soil and stand it at the edge in water no deeper than 30 cm.
5. Water well straight away and keep the soil moist for the first few weeks.
6. Mulch around the base to hold in moisture.

Care

Water

Plenty of water while it is growing and flowering: the soil must never dry out. In summer a pot can stand in a saucer of water.

Feeding

Compost in spring. From May to August, a liquid feed for flowering plants every two weeks, especially in a pot.

Spent flowers

Cut spent flowers off with their stem as low as possible; this keeps the plant tidy and stops it putting energy into seed.

Mulching

In November spread a thick layer of 10–15 cm of straw, leaves or wood chips over the rhizome and remove it again in April.

Dead leaves

In spring, cut away frosted and dead leaves as the new shoots appear.

Tip: Keep the soil wet all summer: the more water, the more flowers. A pot can then happily stand in a saucer of water or at the edge of the pond.

Arum lily: when to prune it?

When: The arum lily is not really pruned. You only cut off spent flower stems in summer and dead leaves in spring.

How:

• Cut spent flowers off with their stem as low as possible.
• Leave frosted leaves in place over winter as extra protection and cut them away in April.
• For a bouquet, cut the stems low down when the spathe has just fully opened.

Caution: Wear gloves: the sap can irritate the skin.

Pruning calendar and basic rules

Propagation

Division

In April–May, as growth starts, lift the clump and cut the rhizome into pieces with a sharp knife, each with a few growing points. Replant straight away 10 cm deep.

Seed

Collect ripe berries in late summer, remove the seeds from the pulp and sow them straight away indoors in moist seed compost at about 20 °C. Seedlings take a few years to flower.

Arum lily: how does it get through the winter?

Hardy to −10 °C: protect in harsh winters.

• Moderately hardy, to about −10 °C: in a sheltered spot it survives most Belgian winters in the ground.
• In November spread a thick layer of 10–15 cm of straw, leaves or wood chips over the rhizome.
• In a pond the submerged rhizome is better protected from frost than in a border.
• In a pot: before the first frost move the pot somewhere cool and frost-free, such as a garage or greenhouse, and keep the compost barely moist.

Diseases and pests

• Slugs and snails: Make holes in young leaves and flowers. Pick them off in the evening and protect the young shoots in spring.
• Aphids: On young leaves and inside opening spathes. Spray off with water; ladybirds usually deal with them.
• No flowers: Too little light, too little water or a plant that is too young. Give it a lighter spot, keep the soil wet and feed in spring.
• Soft rot: Soft, foul-smelling patches on the rhizome and limp, yellow leaves, especially on damaged rhizomes or in a pot kept too warm and wet in winter. Cut away rotten parts or discard the plant.
• Frosted leaves: After a frosty night the leaves turn glassy and then black. Leave them until spring: a well-protected rhizome usually shoots again.

Through the year

• January: Rest. Check that the mulch layer is still thick enough.
• March: Move potted plants into more light and water a little more.
• April: Remove the mulch and cut away dead leaves. Plant and divide.
• May: Plant. Move pots outside after mid-May. Start feeding.
• June: Flowering begins. Water generously. Cut flowers.
• July: Flowering. Water and feed every two weeks. Cut off spent stems.
• August: Flowering. Water. Cut off spent stems.
• September: Stop feeding. Collect ripe berries if you want to sow.
• October: Move pots somewhere frost-free before the first frost.
• November: Thick layer of mulch over the rhizome in the ground.
• December: Rest. Pots cool and frost-free, compost barely moist.

Edible and useful

Not edible. All parts of calla are poisonous: as with its close relative lords-and-ladies, the sap is full of needle-shaped crystals (calcium oxalate) which, when chewed, at once cause a burning pain and swelling of the lips, mouth and throat, with drooling and sometimes difficulty swallowing. Children, and cats and dogs that chew the leaves or flowers, are most at risk; if your cat or dog has chewed it and is drooling or its mouth is swelling, call your vet. Despite the name arum lily, calla is not a true lily: unlike lilies it does not cause kidney failure in cats, but still keep a vase of callas, or a calla in a pot indoors, out of their reach. The sap can irritate the skin: wear gloves when dividing the rhizome or tubers, and wash your hands afterwards. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Did you know?

• The white ‘flower’ is a spathe around a spadix covered in tiny flowers, just like that of lords-and-ladies in our woods, a close relative.
• Linnaeus named the plant Calla aethiopica; later it was given its own genus, named after the Italian botanist Giovanni Zantedeschi. The name calla has stuck.
• ‘Aethiopica’ does not mean it comes from Ethiopia: Europeans once used that name for almost all of Africa south of the Sahara.