How to grow zantedeschia

What are zantedeschias?

These popular plants produce flared, vase-shaped flowers in various bold shades, or elegant white. These stand on upright stems above clumps of lush foliage, making an exotic and striking display in late spring and summer.
 
These plants come originally from swampy regions of eastern or southern Africa, so most like consistently moist soil and warm, sheltered conditions. They are perennials, so will last for many years, most going dormant in autumn then resprouting in spring. Some are hardy, while others are tender.

Hardy zantedeschias (arum lilies)

• Zantedeschia aethiopica is the only hardy species widely available in the UK

• It has large white flowers that stand on sturdy stems up to 90cm (3ft) tall

• The lush, glossy arrow-shaped leaves form bold clumps up to 90cm (3ft) across

• ‘Crowborough’ is the most popular hardy

  Gardeners often use the word variety when referring to a specific plant, but the correct botanical term is 'cultivar'. Whichever word you use, it means a distinctive plant or plants, given a specific cultivar name and usually bred to enhance certain characteristics, such as flower or fruit size, colour, flavour or fragrance, plant size, hardiness, disease resistance, etc. Additionally, it is worth knowing that, botanically, variety has another meaning - it refers to a naturally-occurring distinct plant that only has slight differences in its looks. For example, Malva alcea var. fastigiata differs from typical plants by having an upright habit.

  cultivar and has an RHS Award of Garden Merit for its reliable performance

Tender zantedeschias (calla lilies)

• There are many cultivars, with flowers in a wide range of bright, tropical colours. The lush, glossy leaves are sometimes speckled with white

• These are mainly cultivars of Z. elliottiana and Z. rehmannii (also called Elliottiana hybrids and Rehmannii hybrids).

• They are usually grown as houseplants or temporary summer bedding outdoors

• Most won’t survive below 5˚C (41˚F), so if grown outdoors must be brought in before the first frosts, and kept indoors until after the last frost in spring

• They are more compact than the hardy types, between 30cm (1ft) and 75cm (30in) tall

• They need less water and better drainage than hardy arum lilies, especially in winter

  Overwintering calla lilies

  Calla lilies need a period of dormancy over winter, with little or no water. So once the leaves die down after flowering, move them to a dry, frost-free location, preferably in the dark, until spring.

Choosing the right zantedeschia

Zantedeschias like warm, sheltered conditions, with plenty of light and moisture. They are happy in containers or in the ground, and the more compact, tender types (calla lilies) are ideal in small gardens.

 Zantedeschias suit a wide range of garden styles, including:

• exotic borders
• summer bedding displays
• seaside gardens
• contemporary gardens
• bog gardens and rain gardens
• pond-side plantings – or even in shallow water (Zantedeschia aethiopica only)

Hardy arum lilies can stay outdoors all year round, but tender calla lilies must be brought indoors over winter, so you need to have somewhere

Frost-free environments, such as a cool greenhouse or conservatory, have a nighttime minimum of 4°C (39°F). This is ideal for plants tolerant of low temperatures, but will not survive being frozen, such as tender plants being overwintered including pelargoniums; frost-tender rooted cuttings such as penstemon; and bedding plants in spring.

How and what to buy

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

rhizomes

Where to plant

Zantedeschias can be planted in the ground or in containers. They prefer:

• sun or partial shade – although they usually flower best in full sun
• moist soil that drains well, but doesn’t dry out in summer
• rich, fertile soil, full of organic matter
• a warm, sheltered spot

When to plant

• Plant the bulb-like rhizomes in pots indoors from early spring onwards.
• Plants bought in containers can be planted outside after the last frost. Spring is the best time to plant them, but they are available in summer too, for planting whenever it is not very hot or dry.
• Tender calla lilies must be hardened off before planting out in spring, to acclimatise them to outdoor conditions.

How to plant

Zantedeschias are easiest to plant when bought in containers in full growth, as they can be planted straight into borders or larger containers. They should settle in quickly.
 
If you buy the bulb-like rhizomes (underground stems), these should first be planted in pots indoors to get established, from early spring onwards. Once the young plants are growing strongly, they can be planted outside, after the last frost.  
 
To pot up a dormant rhizome:

• Choose a pot that is just a little larger than the rhizome, and fill with multi-purpose compost
• Plant near the surface, with the top of the rhizome just showing and the shoot buds facing up
• Place the container in a warm, bright spot and water sparingly until shoots appear, usually in a couple of weeks. Rhizomes may rot if overwatered. Once in full growth, water regularly

The process is very similar to planting bulbs – see our guide to planting bulbs in a pot.

Planting in the ground

Plants bought in containers in full growth should settle into borders quickly and easily:

• They like rich soil, so dig in plenty of organic matter, such as garden compost, before planting
• Position the plants at the same level they were growing in the container. Avoid planting too deeply
• Give hardy arum lilies plenty of room – they can form clumps 90cm (3ft) tall and wide
• Plant the smaller tender calla lilies about 30cm (1ft) apart.
• Water in well, then continue watering regularly until established, and during dry spells

For full step-by-step instructions, see our guide to planting perennials.

Planting in containers

• Use a loam-based compost, such as John Innes No 2
• Position the plant in its new container at the same depth it was previously growing
• If planting dormant rhizomes, set them with the tops just showing at the surface and the shoot buds uppermost
• Water regularly when in growth, but little or not at all over winter

See our container planting guide.

Planting in a pond

Zantedeschia aethiopica can be planted in a shallow pond margin:

• Choose a large aquatic basket up to 30cm (1ft) wide
• Fill with aquatic compost or heavy loam
• Position the plant at the same level it was previously growing
• Top off with a layer of gravel to hold the compost in place
• Lower the basket carefully into the pond. Stand it on bricks if necessary, so it is no more than 30cm (1ft) deep

See our guide to planting marginals.

Wet soils: plants for

Wet soils: plants for

Watering

• Newly planted zantedeschias should be watered regularly until established.
• They like consistent moisture, so keep them well watered through the growing season if your soil is at risk of drying out.
• Plants in containers can dry out quickly, as they have less access to water. So these should be watered regularly during the growing season.
• Water only sparingly in winter, otherwise the roots may rot.

Water: collecting, storing and re-using

Water: collecting, storing and re-using

Feeding

Hardy arum lilies should perform well without additional feeding, if grown in fertile soil that is rich in organic matter.

On poorer soils, or to boost growth, you can feed with a balanced liquid fertiliser every fortnight through the flowering period.

Tender calla lilies can be fed during the growing season, especially when in containers:

• Apply a balanced liquid fertiliser fortnightly until the flowers fade
• To boost flowering, you can replace the balanced feed with a potassium-rich feed, such as tomato fertiliser, applying once a week until flowering is over

Container maintenance

Container maintenance

Plant nutrition: feeding plants

Plant nutrition: feeding plants

Mulching

With hardy arum lilies growing in the ground, apply a generous mulch of organic matter, such as well-rotted garden compost, over the root zone in autumn.

This will help to hold in moisture and deter weed germination. It will also insulate the roots, protecting them from freezing over winter.
 

Deadheading

Remove the flowers once they start to fade, pulling out the entire stem at the base.
 
This encourages the formation of new flowering stems, to prolong the display. 

See our guide to deadheading.

Overwintering

In the ground

Hardy Zantedeschia aethiopica and its cultivars can be left in the ground over winter in most parts of the UK.  Still, in all but the mildest areas:

• Lay a thick, insulating layer of mulch on the soil, covering the area in which the roots are growing (typically about 30cm/1ft all round the plant)

• Alternatively, protect the overwintering plants by cutting back and covering with straw or bracken, anchored with pegged-down chicken wire

The older and more established the plant is, the hardier it should be. Young plants should be given extra protection even in mild areas.

Tender calla lilies (mainly cultivars of Z. elliottiana and Z. rehmannii) should be brought indoors over winter, as most will not survive below 5˚C (41˚F). Dig up the plants in autumn, before the first frost, and either:

• Replant into containers and keep them above 10°C (50°F). They need a few months of dormancy, so let the leaves die down and keep them out of bright light, with little or no water

• Cut off the fading leaves and remove the soil from around the bulb-like rhizomes, then dry them off. Store in trays of compost in a cool, dark, frost-free place such as a garage or shed

If you live in a mild area or have a very sheltered garden, you may choose to risk leaving these plants in the ground. If so:

• Insulate the roots with a thick (minimum 15cm/6in) layer of mulch, such as well-rotted garden compost

• Alternatively cover with a cloche or with at least a 15cm (6in) layer of straw/bracken, held in place with chicken wire

Guide to overwintering plants

Guide to overwintering plants

How to prevent winter damage

How to prevent winter damage

In containers

When grown in containers outdoors, the roots are more exposed to the cold, so even hardy types need protection.

• Hardy arum lilies can be left outside if moved to a sheltered spot and/or the container is insulated with several layers of fleece. Hessian and straw are useful plastic-free alternatives

• Tender calla lilies in containers should always be brought indoors. Keep them dry and frost free

How to overwinter plants in a conservatory

How to overwinter plants in a conservatory

Indoors as houseplants

Give calla lilies a period of dormancy over winter, with little or no water, and ideally in the dark. Too much water, especially when not in growth, can cause the rhizomes to rot.

Increase the watering in spring once shoots start to appear, but never let them stand in water.

Caring for older plants

Over time, Zantedeschia aethiopica can form large, dense clumps, and flowering may be reduced due to overcrowding. If this happens, lift and divide the clump in early spring. The resulting smaller plants should be full of vigour and flower well once settled in.
 
See our guide to dividing perennials.

Zantedeschias need no training or pruning. Simply deadhead regularly during the flowering season, and cut away any frost-damaged foliage on hardy plants that are outside over winter.

There are three ways to make new plants:

• By dividing clumps of hardy Zantedeschia aethiopica before growth gets under way in spring. This is very easy and will give you several new plants. Dig up a large established clump and slice through the roots with a spade to create several smaller sections to replant. See our guide to dividing perennials
• By cutting the dormant rhizome into pieces – in spring, larger bulb-like rhizome can be cut into several sections, each with a visible bud. Plant these indoors into pots of multi-purpose compost, then water sparingly until shoots appear. Water regularly and grow on until well established, before planting outside. They many not flower for a year or so, until large enough
• By seed – collect seeds in autumn and store over winter. Sow in spring, one seed per 7.5cm (3in) pot filled with seed compost. Water in, then keep at 21°C (70°F). Seedlings should appear after a few weeks, but plants will not reach flowering size for two or three years

Seed: collecting and storing

Seed: collecting and storing

How to sow seeds

How to sow seeds

Zantedeschias are fairly trouble-free when grown in the right conditions, although temperature and water can cause problems:

• Temperatures below 5˚C (41˚F) can kill tender calla lilies, so bring them indoors before the first frost (see Ongoing care above)
• Most zantedeschias, especially hardy ones, need plenty of water during the growing season. Plants in containers can dry out quickly, so need regular watering. See our guide to container maintenance
• However, too much water can also cause problems, especially in winter. Tender calla lilies need a period of winter dormancy with little or no water. Overwatering, especially while dormant, can cause the rhizomes to rot

When grown indoors or in a greenhouse, they may attract common greenhouse pests, including:

• Aphids
• Red spider mites
• Whitefly 

Controlling pests and diseases without chemicals

Controlling pests and diseases without chemicals

Preventing pest and disease problems

Preventing pest and disease problems