How to grow phormium

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BBC Gardeners' World Magazine

Published: Wednesday, 17 July 2024 at 9:21 am

All you need to know about growing phormium, or New Zealand flax, in our Grow Guide.

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Plant Size:

Height: 200

Spread: 2500

New Zealand Flax, or Phormium, is a handsome long-lived evergreen shrub that forms bold clumps of elongated sword-shaped leaves. The attractive, often colourful foliage looks good all year, and makes the perfect foil for other plants in borders, raised beds, gravel gardens and pots. It has a wide range of leaf colours, including olive-green, purple, yellow, cream, red and apricot variegations, in wide or fine stripes.

Occasionally, phormiums produce flower stems in summer, which are tall and branching with yellow-green, reddish or brown flowers. Plant height and leaf length varies considerably according to the variety of phormium you're growing, from as little as 1m to several metres.

Phormiums originate from New Zealand, where their tough, fibrous leaves were traditionally used in weaving and basket making. Phormiums are moderately hardy once established, although not suitable for cold, exposed sites.

How to grow phormiums

Plant phormiums in spring or early summer in a sunny spot in fertile free-draining soil. Keep moist during dry spells for the first growing season, but after that phormiums growing in the ground need little care and pot-grown plants need only watering.

Growing phormium: jump links

Planting phormium
Caring for phormium
Propagating phormium
Phormium pests and problems
Phormium varieties to grow

Where to grow phormiums

Phormium 'Cream Delight' growing in a mixed border

Phormium 'Cream Delight' growing in a mixed border

Phormiums are suitable for a wide variety of situations around the garden, including coastal locations in milder parts of the country. Plant in beds and borders, on banks, as screen plants, and the smaller varieties are ideal for pots.

Site phormiums in full sun. Cutting back phormiums to reduce their height isn’t possible without spoiling their attractive shape, so choosing the right variety for the site is especially important. Phormiums can survive winter temperatures down to around -5°C if given a sheltered site, although they’re not suited to areas that regularly suffer from long cold spells in winter.

How to plant phormiums

Planting a phormium in a pot

The ideal soil for phormiums is fertile and moisture-retentive yet free-draining. Dig in organic matter such as well-rotted garden compost or soil conditioner before planting, unless the soil is already in good condition.

Dig a hole larger than the roots. Remove the pot and unwind any congested roots, spreading them out in the planting hole. Plant your phormium so the top of the rootball is at ground level, then backfill with the excavated soil and firm in using the heel of your boot.

Water well to settle the soil around the roots and keep moist during dry spells for the first growing season. To grow phormiums in pots, use a soil-based potting compost.

Where to buy phormiums online

How to care for phormiums

Removing dead phormium leaves

Phormiums growing in the ground need little care once established. Mulch the soil annually with composted bark or garden compost to protect the roots from frost and improve the soil, and apply a general fertiliser every spring. Choose a fertiliser that is high in potash to encourage flowering.

Water pot-grown phormiums regularly to keep the soil evenly moist but take care not to overwater them. Feed each spring with a controlled-release fertiliser and pot on into a larger container if the roots are congested.

Keep phormiums looking smart by removing dead leaves and flower stems two or three times a year. Firmly pull leaves that are completely dead to separate them from the plant and avoid a buildup of dead growth. If they won’t detach easily, cut to leave a short section that can be pulled off at a later date.

Mature phormiums can’t be pruned as this would spoil their shape but they can be reduced in bulk by dividing up clumps.

How to propagate phormiums

Divide phormiums in spring, either by digging up and splitting plants that are several years old and have formed good-sized clumps. Alternatively, if the phormium is too large to handle easily, remove the outer sections along with plenty of leaves and roots.

Replant or pot up the divisions at the same depth they were growing previously. As the new divisions can be top heavy, stake and tie for their first year until the roots have become established.

Phormium pests and problems

Given the right growing conditions, phormiums are trouble-free. Mealybugs may occur at the base of leaves, particularly on older plants, but they are usually controlled by birds.

If overexposed on very windy sites, the leaves can be damaged by wind, shredding at the tips and then splitting. Waterlogged soil is liable to cause rotting and plants may die.

Advice on buying phormiums

There are two main types of phormium – Phormium tenax and Phormium cookianum. Phormium tenax (and its cultivars) is compact and grows well in pots. Phormium cookianum is large and makes a huge statement in the garden
While phormiums are readily available from garden centres, you may find more choice at specialist nurseries
Always choose healthy and robust plants, checking them over for signs of pests, damage and disease

Phormium varieties to grow

Phormium tenax

Phormium tenax

Phormium cookianum has light-green leaves and sometimes bears stems of yellow-green flowers. Height x Spread: 2m x 2m
Phormium tenax is larger and more vigorous, with plain dark-green leaves that have blue-green undersides. It sometimes produces tall stems with reddish flowers. H x S: 3m x 2m
Phormium ‘Chocomint’ has green leaves with a broad central chocolate-brown stripe and is compact. H x S: 1m x 1m
Phormium ‘Jester’ is compact with striped with apricot-pink and light-green leaves. H x S: 1m x 1m
Phormium ‘Maori Queen’ has bronze-green leaves, brightly edged with red and a hint of cream. Sometimes sold as ‘Rainbow Queen’. H x S: 1m x 1.2m
Phormium ‘Platt’s Black’ has dark-purple, almost black foliage and a very compact habit. H x S: 60cm x 90cm
Phormium ‘Tricolor’ has light-green leaves boldly edged with cream and red. H x S: 1.5m x 1.5m
Phormium ‘Yellow Wave’ is a vigorous phormium, with large, light-green and yellow-striped leaves that are brighter in spring and mature to yellow-green in summer. Tall stems of red-brown flowers are often borne in summer. H x S: 2m x 2m

Frequently asked questions

What should I do with phormiums in poor condition?

Phormium leaves are likely to show some damage and brown areas at the end of winter. Dead and dying foliage can be removed, but leaves should not be pruned as this spoils the shape of the plant. Phormiums grow best in a sheltered position in free-draining soil, so check that they are situated in a good spot. Congested plants can be dug up, divided and replanted.

How do I protect phormiums in winter?

Phormiums vary in their hardiness. Some are fully hardy and some only borderline hardy, so it is important to know what type you have and whether it will need protection in winter. Phormiums benefit from a winter mulch around the base with a layer of bark or other dry mulch that should be removed in spring. With less-hardy types in colder areas of the UK, wrap the foliage in garden fleece when cold weather is forecast.

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