*Phormium*, *New Zealand flax*: planting, pruning, maintenance

Description and Botany

The genus Phormium includes two species of perennials, the species cookianum or “mountain phormium” and Phormium tenax growing in swampy meadows, along riverbanks and rocky outcrops up to 1,500 m in altitude in New Zealand. While phormium tenax, which is the most commonly cultivated, acclimatises in all our regions, Phormium cookianum, accustomed to humid climates, naturally grows by the seaside, on the oceanic front of our country.

These two species commonly referred to as “New Zealand Flax” belong to the family Agavaceae or Phormiaceae, depending on the classification. They have given rise to numerous hybrids and cultivars offering a wide range of colours and variegated or striped patterns of pink and red, unlike any other plant.

Phormium or New Zealand Flax – Botanical illustration

In its natural habitat, this cousin of the agaves can reach over 3 metres in height. In our gardens, its size is smaller.

Both develop quite rapidly into a large dense rhizomatous clump that is non-running, composed of multiple rosettes with both erect and bushy habits. It can be arched or spreading like a grass, depending on the varieties. Their irregular and charmingly anarchic growth causes some young leaves to arch, while the older, stiffer ones grow at right angles. They beautifully droop to adopt a fountain-like habit in Phormium cookianum.

P. tenax is the largest and most vigorous of the two New Zealand species, reaching on average at maturity 2 to 2.50 m in height in all directions, sometimes more depending on the growing conditions. Phormium cookianum (or P.colensoi) shows less development and forms more modest clumps of 0.60 m to 1.60 m. The cultivars are generally less vigorous than their parents and offer intermediate sizes.

Naturally growing rather slowly, over the years, the bush thickens thanks to its numerous rhizomes allowing it to spread laterally, without ever becoming invasive.

New Zealand Flax is spectacular for its persistent foliage with a very graphic appearance erect like a sword towards the sky. From a bouquet of leaves folded in two at the base, imbricate with each other in a fan shape, arise large linear leaves, leathery like leather, resembling long satin ribbons more or less flexible. Ranging from 0.50 cm to 3 m in length depending on the species, up to 10 cm wide, slightly arched or stiffer, they are pointed and drooping at the tip. The leaves are somewhat narrower and less upright in Phormium cookianum.

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

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

In summer, from May to July, depending on the climate, long flower spikes devoid of leaves appear, towering above the clump of foliage sometimes reaching up to 4 m in height. These small tubular flowers, 2 to 5 cm in size, yellowish-green or dull red at maturity, formed of six petals, bloom in large numbers, grouped in erect panicles.

The flowering leads to the death of the rosette that gave birth to it, but generates the birth of a new shoot.

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

It is followed by the formation of spiralled fruits drooping 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 this beautiful exotic appearance, phormium is more resilient than one might think, tolerating temperatures from -7°C to -10°C, sometimes more depending on the growing conditions. Insensible to diseases and pests, it withstands without flinching, salt spray, pollution, draughts and high heat.

It is a very undemanding plant, easy to grow in regions with mild winters. In open ground, it should therefore be reserved for Mediterranean or Atlantic climates depending on the species where it grows in full sun, in very well-drained, but cool and fertile soil. Elsewhere, growing in a very large pot to be moved to the conservatory in the bad season is more advisable.

Used alone or planted in groups, phormium structures the space and adds an exotic charm to the modern garden as well as to more natural spaces. This plant of New Zealand origin integrates into all decors, its beautiful graphic appearance is precious in contemporary clean and minimalist scenes as well as in gravel gardens or dry gardens. In cold regions, it offers a contemporary note to terraces and balconies.

The Maoris worked the fibres of Phormium as we use flax, for making baskets, ropes, mats, clothing…hence its vernacular name “New Zealand Flax” or “mountain flax.”

Species and main varieties

The most popular

Our favourites

Phormium tenax - New Zealand Flax

This is the largest of the two New Zealand species, but also the most drought-resistant. Perfect for large borders or rockeries

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

See the product sheet

Phormium tenax Variegatum - New Zealand Flax

This lush evergreen perennial offers a particularly exotic appearance to the garden all year round! Perfect for large borders or rockeries

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

See the product sheet

Phormium cookianum subsp. hookeri Tricolor

A variety of beautiful size to use alone or in groups in the garden, as well as 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. We love its very dark fan-shaped silhouette.

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

See the product sheet

Phormium tenax Purpureum - New Zealand Flax

In time, it forms an opulent tuft of linear and stiff foliage, very vertical, with a purple tinged with bronze, giving it a very exotic appearance.

• 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 bright. It forms a beautiful dense tuft with a slightly spreading habit, resembling a large grass.

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

See the product sheet

Phormium Golden Ray - New Zealand Flax

We will appreciate this Phormium for its vigour and bright foliage, composed of long leaves variegated with green and yellow and finely edged with red-orange, gathered in a large tuft of 1.5m.

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

See the product sheet

Phormium tenax Rainbow Sunrise - New Zealand Flax

Sumptuously coloured with the hues of dawn, it forms a tuft that will bring a perfectly exotic touch to any decor.

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

See the product sheet

Phormium tenax Margaret Jones

This Phormium displays magnificent foliage in shades of pink and brown, with purple and shiny reflections.

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

See the product sheet

Young plantation

Where to plant New Zealand flax?

The Phormium is a perennial that is quite tender, especially the coloured forms. Quite sensitive to cold, it can withstand temperatures down to -7°C in the ground, sometimes more, under a well-aerated mulch and in dry, well-drained soil; it is somewhat less hardy in pots. The more colourful forms are less robust.

It is easy to grow in the ground in areas with mild frosts of short duration. Here, it prefers coastal areas; elsewhere, its hardiness is often put to the test. Resistant to wind and sea spray, it is indeed a good plant for coastal areas, ideal for seaside gardens.

Phormium tenax (and its cultivars) is more drought-resistant once well established and may be better suited to Mediterranean climates, while Phormium cookianum prefers the more humid regions of the Atlantic coast, contrary to what is sometimes stated.

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

It does not withstand severe frosts, which is why, in harsher climates, it should be planted in pots and brought indoors for winter. Elsewhere, in regions with a mild climate, plant Phormium in the ground, in full sun, in soft, sandy, well-drained, deep, and fertile soil.

Choose a location that accommodates its height: after 5 years, its silhouette becomes prominent, often occupying more than a metre in width!

Used as a solitary plant or planted in groups, it structures the space and brings verticality and exoticism to the garden. It integrates beautifully into gravel gardens and dry rockeries, as well as in large, slightly blurred perennial beds, to which it adds relief and fullness.

It will add a touch of exoticism 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 and 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 that the plant does not lack water, especially during the first summers following planting.

In the ground

• Loosen the soil well and dig a hole 2 to 3 times the volume of the pot
• Add a good layer of gravel at the bottom of the hole to improve drainage
• Plant the Phormium at collar level in the centre of the hole
• Incorporate a mixture of potting soil for Mediterranean plants and compost into the extracted soil
• Fill the hole and then lightly compact with your foot
• Mulch the base and water generously at planting, then once or twice a week during growth in the first year after planting

In pots

The substrate must be rich and very draining for good root aeration and to avoid stagnant moisture. Place it in full sun.

• In a large pot of at least 50 cm in diameter, spread a good layer of drainage (gravel or clay balls)
• Plant in a mixture of potting soil and slightly sandy garden soil enriched with compost and a handful of crushed horn
• Mulch the base
• In summer, water as soon as the substrate is dry (about once a week)
• Provide a diluted liquid fertiliser in the watering water, once a month during growth
• Bring the pot indoors to protect it from frost in autumn in cold regions and reduce watering and fertiliser: allow the soil to dry between waterings

→ Learn more in our advice sheet: Growing Phormium in pots

Maintenance, pruning and care

Phormium is easy to grow in regions where it does not freeze severely.

In open ground

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

During the first two summers, ensure that the plant does not lack water and that the soil is never too dry or waterlogged: the base should remain cool. Once well established in well-draining soil, it will become increasingly resistant to drought.

After that, water every 15 days, no more, and only in case of prolonged drought in the southern regions of France. Elsewhere, in wetter areas, water more moderately in summer. In winter, it is content with rainwater.

In open ground, phormium does not need fertiliser.

In pots

Potted plants are rather greedy and require more attention. Water generously during the growth period: the soil should never dry out completely. Feed the plant with a diluted liquid fertiliser in the watering water, once a month.

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

How to prune a phormium?

Pruning consists of a simple spring clean-up. From March to April, using pruning shears, cut the faded flower spikes to 20 cm above the ground and trim off any wilted or withered leaves.

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

Diseases and potential pests

Phormium is very little sensitive to parasitic pests, diseases, and atmospheric pollution. However, young plants may suffer from attacks of mealybugs, identifiable by the cottony masses they leave on the plant. They slow down growth and discolour the foliage. Treat with sprays of rapeseed oil. 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. Dividing a large clump can be quite challenging, as phormium is one of the toughest! Avoid damaging the fragile roots.

• Using a spade, clear young shoots from the periphery (or a nice clump) while avoiding damaging the roots
• Trim the leaves by half
• Replant the shoots in individual pots or the clump in the ground in a hole that is wide and deep enough, enriched with a well-draining mix of potting soil and gravel
• Backfill, firm down well, then water generously and keep the soil moist but not waterlogged until growth resumes

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

Pairing Phormium

New Zealand flax with its spectacular ribbon-like leaves in surprising colours ranging from olive green to black purple, with cream-white, pink, or apricot variegations, standing erect in a sword-like shape, is always a significant focal point in a garden or in a pot on a balcony or terrace.

Its sharp yet elegant foliage, its beautiful graphic silhouette all year round, lends itself to multiple uses and always brings character, exoticism, and verticality to a decor. It allows for the creation of original and highly colourful scenes.

An undisputed star of exotic, contemporary, or Mediterranean-inspired gardens, phormium fits into all gardens, even coastal ones, whether structured, wild, or natural, providing relief and breadth 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 structure a border of perennials and small bushes. Used in isolated clumps, they also make very ornamental ground covers underplanted with trailing perennials such as verbena, petunias, or delospermas.

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

Companion plants may fade over the seasons, but the phormium will continue to attract attention with its long, colourful straps.

In natural scenes, it will make a sensation mixed with large grasses like pennisetums or miscanthus, allowing for magnificent combinations of shapes based solely on the interplay of evergreen foliage.

A contrasting association: phormium tenax variegatum, framed by two Mexican orange blossoms (Aztec Pearl and Sundance) and accompanied by a border of Festuca glauca.

For a contrasting atmosphere, the pink and purple varieties (‘Evening’, ‘Margaret Jones’, ‘Pink Panther’) will enhance each other alongside an Leptospermum scoparium ‘Red damask’, with its long flowering period of deep red, a tuft of Muhlenbergia capillaris, a true pink cloud at the end of summer, the Great melianthus, a Leucadendron ‘Safari Sunset’, a Colocasia Sangria, 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, mineral lines like a scree garden or dry garden, it pairs wonderfully with other equally graphic and easy-to-maintain plants such as bamboos, cordylines, and yuccas in very contemporary compositions. It is a remarkable plant that combines well with the lush foliage of banana plants or the structuring architecture of palms, a Dasylirion glaucophyllum, or agaves.

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

In a large pot, it will create a sumptuous effect in a carpet of verbenas or paired with a pelargonium, giving a truly exotic appearance alongside a Trachycarpus wagnerianus or miniature palm.

→ Discover more association ideas with Phormium in our advice sheet!