Phormium, New Zealand flax: planting, pruning, care

Description and botany

Genus Phormium includes two species of perennials, the species cookianum or “mountain phormium” and Phormium tenax, which grow in marshy meadows, along watercourses and on rocky escarpments up to 1 500 m altitude in New Zealand. While Phormium tenax, the species most commonly cultivated, acclimatises to all our regions, Phormium cookianum, accustomed to humid climates, naturally grows by the sea on our ocean-facing coasts.

These two species, commonly called “New Zealand flax”, belong to family Agavaceae or to Phormiaceae, depending on classification. They have produced numerous hybrids and cultivars offering a wide palette of colours and variegations or pink- and red-striped patterns unlike any other plant.

Phormium or New Zealand flax – botanical illustration

In its natural habitat, this cousin of agaves can reach over 3 metres in height. In gardens, plants are usually smaller.

Both develop fairly quickly into a broad, dense rootstock clump that is not running, composed of many rosettes with a habit both erect and bushy. Habit may be arching or flared like a grass, depending on cultivar. Their growth is irregular and agreeably anarchic: some leaves arch when young while older, stiffer leaves grow at right angles. They arch gracefully to form a fountain-like habit in Phormium cookianum.

P. tenax is the larger and more vigorous of the two New Zealand species and typically reaches at maturity 2 to 2.50 m in all directions, sometimes more depending on growing conditions. Phormium cookianum (or P. colensoi) shows less vigour and forms more modest clumps of 0.60 m to 1.60 m. Cultivars are generally less vigorous than their parents and offer intermediate sizes.

Naturally rather slow-growing, the clump thickens over the years thanks to numerous rootstocks that allow lateral spreading without ever becoming invasive.

New Zealand flax is spectacular for its evergreen foliage with a very graphic appearance, sword-shaped and erect towards the sky. From a bundle of leaves folded at the base and imbricated like a fan arise , leathery as leather, resembling long satin ribbons that are more or less flexible. From 0.50 cm to 3 m long according to species, up to 10 cm wide, slightly arched or stiffer, they are pointed and trailing at the tip. Leaves are somewhat narrower and less erect on Phormium cookianum.

The two species have produced many hybrids offering an infinity of solid colours, sumptuously variegated tones or subtly striped shades of cream, copper, yellow, green, bronze-tinged orange, bluish bronze or purple. Green-yellow in variety Golden Ray, almost black in Phormium cookianum Black Adder, orange-pink to purplish-pink in ‘Margaret Jones’, apricot-pink edged with olive green to bronze-green in ‘Rainbow Sunrise’, tones of pink, purple, bronze, brown and ruby-red in ‘Pink Panther’, or pale yellow tinted lime-green and traversed by numerous green striations along their length in ‘Yellow Wave’.

If this perennial surprises with the brightness and range of its foliage, its flowering, when it occurs after several years of cultivation, is equally remarkable. Flowering is rare and even scarce in some varieties.

In summer, from May to July depending on climate, long leafless flower stems appear above the foliage clump, sometimes reaching up to 4 m in height. Small tubular flowers 2 to 5 cm long, greenish-yellow or dull red at maturity, consisting of six petals, open in large numbers, grouped in upright panicles.

Flowering causes the rosette that produced it to die, but generates the birth of a new shoot.

This very nectariferous flowering attracts certain birds and many pollinating insects.

It is followed by formation of spiralled fruits that are pendulous in Phormium cookianum or erect in Phormium tenax, appearing as capsules filled with seeds dispersed by wind at maturity.

Phormium tenax hybrid, leaves, flowers and pods containing seeds

Beneath this exotic appearance, phormium is hardier than expected, tolerating temperatures from -7°C to -10°C, sometimes lower depending on growing conditions. Unaffected by disease and pests, it tolerates sea spray, pollution, wind and high heat without complaint.

It is very undemanding and easy to grow in regions with mild winters. In open ground, reserve it for Mediterranean or Atlantic climates according to species, where it grows in sun in very well-drained yet cool, fertile soil. Elsewhere, growing in a very large pot and sheltering in a conservatory during the bad season is preferable.

Used as a solitary specimen or planted in groups, phormium structures space and brings an exotic charm to modern gardens as well as more natural settings. This New Zealand native fits into all landscapes, its striking graphic habit being especially valuable in contemporary minimalist scenes as well as in rock gardens or dry gardens. In cold regions, it adds a contemporary note to terraces and balconies.

Maori worked Phormium fibres as we use flax to make baskets, ropes, mats, clothing… hence its vernacular name of “New Zealand flax” or “mountain flax”.

Species and main varieties

Most popular

Our favourites

Phormium tenax - New Zealand Flax

It is the largest of the two New Zealand species, and also the most drought-resistant. Perfect for large beds or large rockeries

• Flowering time July, August
• Height at maturity 2 m

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Phormium tenax Variegatum - New Zealand Flax

This lush evergreen perennial lends a particularly exotic look to the garden year-round! Perfect for large beds or large rockeries

• Flowering time July, August
• Height at maturity 2,50 m

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Phormium cookianum subsp. hookeri Tricolor

An attractively sized variety to use as specimen or in groups in garden, or planted in a very large pot on terrace or balcony

• Flowering time July, August
• Height at maturity 1,50 m

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Phormium cookianum Black adder

A magnificent evergreen perennial with very exotic appearance. Its very dark fan-shaped silhouette is much admired.

• Flowering time July, August
• Height at maturity 1,20 m

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Phormium tenax Purpureum - New Zealand Flax

It eventually forms an opulent clump of linear, stiff, very upright foliage, purple tinged with bronze, very exotic in appearance.

• Flowering time July, August
• Height at maturity 2,50 m

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Phormium cookianum subsp. hookeri Cream Delight

This variety is compact and particularly luminous. It forms a beautiful dense clump with a slightly flared habit, somewhat reminiscent of a large grass.

• Flowering time July, August
• Height at maturity 75 cm

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Phormium Golden Ray - New Zealand Flax

This Phormium is prized for vigour and bright foliage, composed of long leaves variegated green and yellow and finely edged in red-orange, forming a large 1.5 m clump.

• Flowering time July, August
• Height at maturity 1,50 m

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Phormium tenax Rainbow Sunrise - New Zealand Flax

Sumptuously coloured with dawn hues, it forms a clump that will bring a perfectly exotic touch to any setting.

• Flowering time July to September
• Height at maturity 1 m

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Phormium tenax Margaret Jones

This Phormium unfurls magnificent foliage in pink and brown tones, with purple, glossy highlights.

• Flowering time July, August
• Height at maturity 90 cm

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Planting

Where to plant New Zealand flax?

Phormium is a fairly tender perennial, particularly the coloured forms. Quite frost‑sensitive, it nevertheless withstands down to -7°C in ground, sometimes more, under a well‑aerated mulch and in dry, well‑drained soil; it is a little less hardy in a pot. The most colourful forms are less robust.

It is easy to to grow in ground where frosts are light and short‑lived. Here, it prefers coastal locations; elsewhere its hardiness is often severely tested. Resistant to wind and sea spray, it is a good plant for the seaside, ideal for coastal gardens.

Phormium tenax (and its cultivars) is more drought‑resistant once well established and perhaps better suited to Mediterranean climates, while Phormium cookianum prefers wetter Atlantic coastal regions, contrary to what is sometimes written.

Both prefer deep soil that stays cool in summer and does not dry out, to develop well into clumps.

It does not withstand severe frosts, which is why in colder climates it should be grown in a pot and brought indoors for winter. Elsewhere, in regions with a mild climate, plant Phormium in ground, in full sun, in loose, rather sandy, well‑drained, deep and fertile soil.

Choose a position suitable for its eventual size: after five years its habit becomes apparent, often occupying more than one metre in width!

Used as a specimen or planted in groups, it structures space and brings verticality and an exotic feel to the garden. It fits wonderfully into gravel gardens and dry rockeries, as well as in large drifts of slightly informal perennials, to which it adds relief and scale.

It will add an exotic touch to balconies, terraces and urban gardens.

When to plant Phormium?

Planting New Zealand flax is preferably done in spring, from March to April or in late summer, from September to October.

How to plant Phormium?

In rich, well‑drained soil, Phormium will be more vigorous and more tolerant of frost. If your soil retains moisture, do not hesitate to plant your Phormium on top of a mound, where water will not stagnate. However, ensure the plant does not lack water, particularly during first summers after planting.

In ground

• Loosen soil well and dig a hole 2 to 3 times pot volume
• Add a good layer of gravel to bottom of hole to improve drainage
• Plant Phormium at collar level in centre of hole
• Mix in a blend of potting compost for Mediterranean plants and compost into excavated soil
• Refill hole then firm lightly with foot
• Mulch base and water abundantly at planting then once to twice a week during growth in first year after planting

In a pot

Substrate must be rich and very free‑draining for good root aeration and to avoid stagnant moisture. Place in full sun.

• In a large pot of at least 50 cm diameter, lay a good drainage layer (gravel or clay pebbles)
• Plant in a mix of potting compost and slightly sandy garden soil enriched with compost and a handful of horn meal
• Mulch base
• In summer, water as soon as substrate is dry (about once a week)
• Apply a liquid fertiliser diluted in watering water once a month during growth
• Bring pot inside to shelter from frost in autumn in cold regions and reduce water and fertiliser: let soil dry between waterings

→ Learn more in our advice sheet : How to grow Phormium in a pot

Maintenance, pruning and care

Phormium is easy to grow in regions where winters are not harsh.

In open ground

Protect plant base with a thick mat of gravel or dead leaves to conserve soil moisture in summer and protect roots from cold in winter. In harsh climate, wrap foliage in winter protective fleece.

During first two summers, ensure plant does not lack water and that soil is never too dry nor waterlogged: plant base must remain cool. Once well established in well‑draining soil, it will become increasingly drought‑resistant.

Thereafter, water every two weeks, no more, and only in case of prolonged drought in southern France. Elsewhere, in wetter regions, water more moderately in summer. In winter, it survives on rainfall.

In open ground, Phormium does not need fertiliser.

In pots

Plants grown in pots are fairly demanding and require more attention. Water abundantly during period of growth: soil must never dry out completely. Feed plant with a liquid fertiliser diluted in watering water, once a month.

In winter, reduce waterings and fertiliser applications, and allow soil to dry between waterings. Repot every 2 years.

How to prune Phormium?

Pruning is limited to a simple spring tidy. From March to April, using a pruning shear, cut spent flower stems 20 cm from soil and cut faded or withered leaves back to ground level.

Read also : Phormium: how to protect it from cold and overwinter it?

Potential diseases and pests

Phormium is little affected by parasitic organisms, diseases or air pollution. Young plants can, however, suffer attacks by mealybugs, recognisable by the cottony masses they leave on the plant. They slow growth and discolour the foliage. Treat with rapeseed oil sprays. Repeat two or three times at 15-day intervals.

Propagation

Sowing is possible in February–March but we recommend instead the removal of young shoots in autumn. The division of a large clump can prove quite difficult, phormium being particularly tough! Avoid damaging fragile roots.

• With a spade, free young shoots at the edges (or a good-sized clump), taking care not to damage the roots
• Cut leaves back by half
• Replant offsets into individual pots or plant the clump in the ground in a hole large and deep enough, enriched with a well-draining mix of potting compost and gravel
• Backfill, firm down, then water generously and keep soil moist but not waterlogged until growth resumes

→ Learn more about dividing Phormium in Alexandra’s tutorial!

Companion plants for Phormium

New Zealand flax with its spectacular ribbon-like leaves in striking colours ranging from olive green to almost black-purple and including cream, pink or apricot variegations, upright and sword-shaped, is always an important focal point in a garden or in a pot on a balcony or terrace.

Its sharp yet elegant foliage and its striking year-round silhouette lend themselves to many uses and always bring character, exoticism and verticality to a setting. It allows the composition of original and very colourful scenes.

Undisputed star of exotic-, contemporary- or Mediterranean-inspired gardens, phormium fits into all gardens, even coastal ones, whether structured, wild or natural, where it provides relief and scale throughout the four seasons.

With their architectural habit, large phormiums (Phormium tenax ‘Purpureum’, Phormium tenax ‘Variegatum’) are perfectly suited to create a spectacular centre of interest and to structure a bed of perennials and small bushes. Used in isolated clumps, they also make very ornamental groundcovers underplanted with mat-forming perennials such as verbenas, petunias or delospermas.

Easy to combine with each other or to associate with other Asian plants, such as Japanese grasses, they also appreciate the company of Chinese palms. For a modern bed with an exotic feel, surround them with giant cannas, large dahlias and bulbs of Watsonias, Kniphofias, Crocosmias.

Companion plants may die back over the seasons, but phormium will continue to draw the eye with its long colourful straps.

In naturalistic scenes, it makes a striking combination when mixed with large ornamental grasses such as pennisetums or miscanthus, allowing magnificent pairings of form based solely on interplay of evergreen foliage.

A contrasting combination: Phormium tenax ‘Variegatum’, flanked by two Mexican orange blossom (Aztec Pearl and Sundance) and accompanied by a border of Festuca glauca.

For a contrasting scheme, pink and purple varieties (‘Evening’, ‘Margaret Jones’, ‘Pink Panther’) will complement each other when paired with Leptospermum scoparium ‘Red Damask’, with a clump of Muhlenbergia capillaris, a true pink cloud in late summer, with Melianthus major, with Leucadendron ‘Safari Sunset’, with a Colocasia ‘Sangria’, with Lophomyrtus ‘Magic Dragon’, or with Callistemon or Ricinus communis ‘Carmencita Rouge’.

A pink-toned combination: Phormium tenax ‘Evening Glow’, Leucadendron ‘Safari Sunset’, Colocasia ‘Sangria’ and Muhlenbergia capillaris

In a modern garden with clean, mineral lines such as a scree garden or dry garden, it pairs wonderfully with other equally architectural and easy-care plants such as bamboos, cordylines and yuccas in very contemporary compositions. It is a remarkable plant that also harmonises with lush foliage of banana plants or with the structural architecture of palms, a Dasylirion glaucophyllum or agaves.

In a seaside garden, it is the ideal companion for plants that, like it, come from Oceania such as Pittosporum tenuifolium ‘Tom Thumb’, Pseudopanax ferox or Olearia macrodonta ‘Major’ (New Zealand holly).

In a large pot, it will produce a sumptuous effect in a tapetum of verbenas or, when paired with a pelargonium, will give a truly exotic aspect alongside a Trachycarpus wagnerianus or miniature palm.

→ Discover other ideas for pairing with phormium in our advice sheet !