<em>Phormium</em>, New Zealand flax: planting, pruning, care

Description and botany

Genus Phormium comprises two perennial species, P. cookianum or “mountain phormium” and Phormium tenax, which grow in swampy meadows, riverbanks and rocky escarpments up to 1,500 m altitude in New Zealand. While Phormium tenax, the most commonly cultivated species, acclimatises to all our regions, Phormium cookianum, accustomed to humid climates, naturally grows by the sea on our country’s oceanic coast.

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

Phormium or New Zealand flax – Botanical illustration

In its natural habitat, this cousin of agaves can reach more than 3 metres in height. In our gardens, it is smaller.

Both develop fairly rapidly into a large, dense, non-running rootstock clump composed of multiple rosettes with an upright yet bushy habit. It can be arched or flared like a grass, depending on variety. Their irregular, charmingly anarchic growth makes some leaves arch when young, while older, stiffer leaves grow at right angles. They bend gracefully into 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 2.5 m in all dimensions, sometimes more depending on growing conditions. Phormium cookianum (or P. colensoi) shows less development and forms more modest clumps of 0.6 m to 1.6 m. Cultivars are generally less vigorous than their parents and offer intermediate sizes.

Of naturally rather slow growth, over the years the clump thickens thanks to its many rootstocks which allow it to spread laterally without ever becoming invasive.

New Zealand flax is spectacular for its evergreen foliage with a very graphic, sword-like habit pointing skywards. From a cluster of leaves folded in two at the base, imbricated like a fan, emerge large linear leaves, leathery and resembling long satin-like ribbons of varying flexibility. Ranging from 0.5 m to 3 m in length depending on species and up to 10 cm wide, slightly arched or stiffer, they are pointed and droop at the tip. Leaves are a little narrower and less erect in Phormium cookianum.

Both species have produced many hybrids offering an endless variety of solid colours, sumptuously variegated shades or subtly striate patterns of cream, copper, yellow, green, bronzed orange, bluish bronze or purple. Green-yellow in variety Golden Ray, almost black in Phormium cookianum Black Adder, pink-orange to pink-purple 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 tinged with lime and traversed by numerous green striations along their entire length in ‘Yellow Wave’.

While this perennial astonishes with the luminosity and breadth of its foliage, its flowering, when it occurs after several years in cultivation, is equally remarkable. It is rare and even sparse in some varieties.

In summer, from May to July depending on climate, long leafless flowering scapes appear above the clump of foliage, sometimes reaching up to 4 m high. These small tubular flowers, 2 to 5 cm long, yellow-green or dull red at maturity and formed of six petals, open in large numbers and are grouped in erect panicles.

Flowering causes the death of the rosette that produced it, but generates the appearance of a new offset.

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

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

Phormium tenax hybrid, leaves, flowers and pods containing the seeds

Beneath its exotic appearance, phormium is hardier than it looks, tolerating temperatures from -7°C to -10°C, sometimes lower depending on growing conditions. Resistant to diseases and pests, it endures sea spray, pollution, draughts and high temperatures without complaint.

It is a very undemanding plant, easy to grow in regions with mild winters. In the ground, it is therefore best reserved for Mediterranean or Atlantic climates depending on species, where it grows in sun in very well-drained but fresh and fertile soil. Elsewhere, cultivation in a very large pot moved into the conservatory for the cold season is more appropriate.

Used as a specimen or planted in groups, phormium provides structure and lends an exotic charm to modern gardens as well as more natural spaces. This plant of New Zealand origin fits into all settings; its strong graphic presence is valuable in pared-back contemporary scenes and minimalist layouts such as gravel gardens or dry gardens. In cold regions, it brings a contemporary note to terraces and balconies.

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

Species and main varieties

Most popular

Our favourites

Phormium tenax - New Zealand Flax

It’s the larger of the two New Zealand species, but also the most drought‑tolerant. Perfect for large beds or big rockeries

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

See the product sheet

Phormium tenax Variegatum - New Zealand Flax

This luxuriant evergreen perennial gives a particularly exotic look to the garden all year round! Perfect for large beds or big rockeries

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

See the product sheet

Phormium cookianum subsp. hookeri Tricolor

A well-sized variety to use as a specimen or in groups in the garden, or planted in a very large pot on the terrace or balcony

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

See the product sheet

Phormium cookianum Black adder

A magnificent evergreen perennial with a very exotic appearance. Admired for its very dark fan-shaped habit.

• 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 in purple with bronze tones, creating a very exotic effect.

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

See the product sheet

Phormium cookianum subsp. hookeri Cream Delight

This variety is compact and particularly striking. It forms a beautiful dense clump with a slightly flared habit, somewhat resembling a large grass-like plant.

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

See the product sheet

Phormium Golden Ray - New Zealand Flax

This Phormium is valued for its vigour and luminous foliage, composed of long variegated green-and-yellow leaves finely edged in orange‑red, forming a large clump about 1.5 m across.

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

See the product sheet

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

See the product sheet

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

See the product sheet

Planting

Where to plant New Zealand flax?

Phormium is a perennial not very hardy, especially the colourful forms. Rather tender, it still tolerates down to -7°C in ground, sometimes more, under a well-aerated mulch and in dry, well-drained soil; it is somewhat less hardy in a pot. The most colourful forms are less robust.

It is easy to grow in ground where frosts are light and short-lived. Here, it prefers seaside 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 established and perhaps better suited to Mediterranean climates, while Phormium cookianum prefers Atlantic coastal regions, which are more humid, contrary to what is sometimes written.

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

It does not withstand severe frosts; therefore, in harsher climates it should be planted in a pot and brought indoors for winter. Elsewhere, in regions where climate is mild, plant Phormium in ground, in sun, in a loose, rather sandy, well-drained, deep and fertile soil.

Choose a spot fitting its eventual size: after 5 years its silhouette is established, often occupying more than 1 metre in width!

Used singly or planted in groups, it structures space and adds verticality and exoticism to gardens. It fits wonderfully into gravel gardens and dry rockeries, as well as into large, slightly informal perennial beds, to which it brings relief and scale.

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

When to plant Phormium?

Preferably plant New Zealand flax in spring, from March to April or in late summer, September to October.

How to plant Phormium?

In rich, well-drained soil, Phormium will be more vigorous and more tolerant of frost. If soil retains moisture, don’t hesitate to plant Phormium on top of a raised mound, where water will not stagnate. However, ensure plant does not lack water, particularly during first summers following 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
• Incorporate a mix of potting compost for Mediterranean plants and compost into excavated soil
• Fill hole then firm gently with foot
• Mulch the base and water generously at planting then once or twice a week during growth in first year after planting

In pot

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

• In a large pot at least 50 cm in 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 the base
• In summer, water as soon as substrate is dry (about once a week)
• Apply a diluted liquid feed with watering, once a month during growth
• Bring pot indoors to protect from frost in autumn in cold regions and reduce water and feed: let soil dry between waterings

→ Find out more in our advice sheet : Growing Phormium in a pot

Maintenance, pruning and care

Phormium is easy to grow in regions where there are no severe frosts.

In open ground

Protect plant’s 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 climates, wrap foliage with a winter fleece.

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

After that, water every fortnight, no more, and only in case of prolonged drought in southern France. Elsewhere, in wetter regions, water more moderately in summer. In winter, it is content with rainwater.

In open ground, phormium does not need fertiliser.

In pots

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

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

How to prune Phormium?

Pruning is limited to a single spring tidy-up. From March to April, using pruning shears, cut spent flower scapes to 20 cm above soil level and cut faded or withered leaves back to soil level.

See also: Phormium: how to protect from cold and overwinter?

Possible diseases and pests

Phormium is largely unaffected 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.

Multiplication

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

• Using a spade, loosen young shoots at the edge (or a healthy clump), taking care not to damage the roots
• Cut leaves back by half
• Replant shoots into individual pots or set clump directly into ground in a hole large and deep enough, enriched with a well-draining mix of potting compost and gravel
• Backfill, firm down well 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 surprising colours ranging from olive green to near-black purple and including cream‑white, pink or apricot variegations, held upright in a sword shape, is always an important focal point in a garden or in a pot on a balcony or terrace.

Its sharp yet elegant foliage and graphic silhouette, attractive all year round, lend themselves to many uses and always bring character, exoticism and verticality to a setting. It enables the composition of original and very colourful scenes.

Undisputed star of exotic, contemporary or Mediterranean-inspired gardens, phormium fits into all gardens, even coastal, whether structured, wild or natural, to which it offers throughout the four seasons relief and presence.

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 planting of perennials and small bushes. Used as 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 with other Asian plants, such as Japanese grasses, they also appreciate the company of Chinese palms. For a modern bed with exotic airs, surround them with giant cannas, large dahlias and bulbs of Watsonias, Kniphofias, Crocosmias.

Companion plants may disappear over the seasons, phormium will continue to attract the eye with its long colourful leaf blades.

In naturalistic scenes, it will make a sensation when mixed with large grasses such as pennisetums or miscanthus, allowing magnificent pairings of forms founded solely on the play 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 mood, pink and purple varieties (‘Evening’, ‘Margaret Jones’, ‘Pink Panther’) will enhance each other with a Leptospermum scoparium ‘Red damask’, with its long flowering of deep red, a clump of Muhlenbergia capillaris, a true pink cloud in late summer, a giant melianthus, a Leucadendron ‘Safari Sunset’, a Colocasia Sangria, a Lophomyrtus ‘Magic Dragon’ or even Callistemon or Ricinus communis ‘Carmencita rouge’.

An association in pink tones: Phormium tenax Evening Glow, Leucadendron Safari Sunset, Colocasia Sangria and Muhlenbergia capillaris

In a modern garden with clean lines, mineral and pared-back, such as a scree garden or dry garden, it pairs wonderfully with other plants equally graphic and easy to grow such as bamboos, cordylines, yuccas in very contemporary compositions. It is a remarkable plant that pairs well with lush foliage of banana plants or with the structuring architecture of palms, a Dasylirion glaucophyllum or agaves.

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

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

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