Arum Lily: These Plants Will Thrive Growing In Moist Soil, But Often Need Winter Protection
Reviewed By COLIN SKELLY
Colin is a Horticulturist and Horticultural Consultant with experience in a range of practical and managerial roles across heritage, commercial and public horticulture. He holds the Royal Horticultural Society’s Master of Horticulture award and has a particular interest in horticultural ecology and naturalistic planting for habitat and climate resilience.
IN THIS GUIDE
The Arum Lily produces a flower that is simple yet chic, looking for all the world like a designer-sculpted piece in minimalist style.
One attribute that is definitely not minimalist is the amazingly wide range of brilliant ‘popping’ colours this flower comes in.
Not a true flower, the form comprises a one-sheet ‘scarf’ – the bract – wrapped around a bright spike – the inflorescence.
Overview
| Botanical Name | Zantedeschia aethiopica |
| Common Name(s) | Arum Lily |
| Plant Type | Perennial |
| Native Area | South Africa / Lesotho |
| Hardiness Rating | H4 |
| Foliage | Herbaceous or semi-evergreen |
| Flowers | White, funnel-shaped flowers |
| When To Sow / Plant Out | March, April, May |
| Flowering Months | June, July, August |
Sunlight
Preferred
Full Sun or Partial Shade
Exposure
Sheltered
Size
Height
0.5 – 1M
Spread
0.1 – 0.5M
Bloom Time
May – August
Soil
Preferred
Clay, loam
Moisture
Poorly drained
pH
Any
Whoever has seen an Arum Lily knows that it is not a ‘regular’ flower.
It features a prominent central protuberance, wrapped around by a single long petal as if it were a scarf.
They come in somewhat different dimensions and appearances and in quite a range of colour tones.
In fact, that protuberance is a spadix – a spike that is actually an inflorescence of tiny florets.
And that long, wrap-around ‘petal’ is the spathe which is a type of bract – a special raised leaf that is typically coloured and shields one or more flowers.
What is called ‘Arum Lily’ is not really a lily at all.
It is not even a member of the Lily family – Liliaceae – let alone the Lily genus – Lilium.
The Arum Lily is a member of Genus Zantedeschia within the Family Araceae.1Report: Zantedeschia aethiopica. (n.d.). ITIS. Retrieved March 9, 2023, from https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=42555#null
Various species of the Zantedeschia genus are often interchangeably called ‘Arum Lily’ and ‘Calla Lily’, especially in North America.
In this guide we refer only to species Zantedeschia aethiopica and its cultivars as ‘Arum Lily’.
The species bears a flower that has a pure white spathe encircling a sunny yellow spadix.
Cultivars produce flowers with spadices in colours ranging from creamy white through pale orange to deep purple and even glazed black, and spathes in hues ranging from white and pastel pink to deep purple and grey-purple to blackish hues.
Habitat & Growing Conditions
Z. aethiopica is native to the southeastern region of South Africa.2Zantedeschia aethiopica. (n.d.). Kew Royal Botanic Gardens. Retrieved March 9, 2023, from https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:89403-1
It has been naturalised in quite a disparate patchwork of regions and countries on all continents (except Antarctica) including the United Kingdom.
The plant inhabits all types of damp low-lying ground.
It grows in fields and meadows by waterways and ponds, and even in swamps and marshes in its native habitat in (some provinces of) South Africa.
In the wild it is not found in dry ground or in the highlands.
Z. aethiopica itself and some cultivars are hardy to H4 which means that they are ‘just enough’ hardy in the United Kingdom and are best protected during the winter while most cultivars are hardy only to H1C – basically, not hardy at all.
Where To Grow Arum Lily
If you live in a region that does not suffer from frost or frigid winters, you can plant the species and those cultivars that are hardy to H4 in beds and, ideally, near ponds and any other waterways where these plants will thrive in the moist soil, though they would need winter protection.
Because of its habitat preferences, this plant is a natural choice for water gardens; and because of its ‘flower’, it is a great choice for contemporary gardens and modernist, minimal-style gardens.
“I plant Arum Lily for its leaves as well as its flowers,” shares Consultant Horticulturist Colin Skelly.
“The foliage of the Arum Lily is exotic and can work with other foliage plants to create an exotic feel, particular around water.
“Its flowers have an otherworldly quality to really catch the attention in summer, shining out in the partial shade that they favour.”
The unusual ‘flower’ makes Arum Lily a top choice as a specimen plant to be grown in containers set by the doorway or on a parapet, some cultivars being more suited to such display than others.
If you grow the tender cultivars in containers you will not only get an accent plant with a most unusual flower, it will be very convenient to overwinter indoors or in a greenhouse.
Though the Arum Lily’s water needs are high, their sunlight needs are low, so they can make very attractive year-round houseplants.
How To Grow Arum Lilies
Although Arum Lilies can be grown from seed, the plants will not bloom until the third year so they are most commonly grown from rhizomes.
Also, seeds require a consistent temperature within a very narrow range to germinate.
Avoid growing cultivars with a hardiness rating of H1C in the ground, otherwise you will have to remove the rhizomes every autumn and store them indoors, making sure that they are kept damp.
If you grow the H4 varieties outdoors then, in more regions of the United Kingdom than not, you will be able to allow them to stay in the ground through the winter; simply protect the rhizomes with horticultural fleece or a layer of leaf mulch.
Planting
Rhizomes of the H4 cultivars may be planted outdoors after the last frost has well passed.
They should be planted about 10cm deep such that their eyes just ‘peek’ out of the soil’s surface.
Space them about 40cm apart. Rhizomes of any and all hardiness ratings may also be planted in containers.
Plant Care
In most regions of the United Kingdom, sites with dappled sunlight will prove best through full sun or morning sun will also do nicely.
A sheltered location facing south through west is preferable.
Soil Requirements
Soil should be of a rich and fertile type incorporating organic content, such as well-rotted manure or humus, in a loam that contains clay, silt, and sand.
If your soil is lacking in clay or manure then amend it with vermiculite for water retention.
Watering & Feeding
Arum Lilies, especially during the growing season, should be watered well; ensure that the soil is consistently moist.
Just before the start of flowering season, Arum Lily may be fertilised with a slow-release organic fertiliser with a balance of approximately 5-10-10.
Otherwise fertilise it with a ‘regular release’ fertiliser, applied in moderation, every two to three weeks.
Overwintering
As mentioned above, the semi-hardy varieties’ rhizomes may be kept outdoors if they are protected by leaf mulch or a layer of fleece.
Arum Lilies growing in pots may be brought indoors (or kept in a greenhouse) before winter.
They can grace a room in your home in a spot where they get a few hours of sunlight or several hours of indirect light.
If outdoor plants have not dropped their leaves in winter, cover them with a lightweight horticultural fleece.
Pruning
Arum Lilies do not need to be pruned. You may trim overgrown plants if they look unkempt.
Any leaves that winter frost has blackened should be cut off.
Common Problems
Arum Lilies are quite vigorous plants. On occasion they may succumb to aphids and sometimes to thrips.
Thrips are the more troublesome pests; any parts of a plant that show signs of a thrip infestation should be pruned and disposed off.
Thrips can be treated with a combination of insecticidal soap, (diluted) Neem Oil and beneficial predators like ladybugs.