Horticulture Magazine

Phormium ‘New Zealand Flax’ Plant Care & Growing Tips

phormium new zealand flax up close

Phormium Overview

Official Plant NamePhormium
Common Name(s)New Zealand Flax
Plant TypePerennial
Native AreaNew Zealand
Hardiness RatingH4
ToxicityNone
FoliageEvergreen
FlowersInconspicuous tubular flowers
Plant OutMarch, April, May
Flowering MonthsJuly, August
When To PruneMarch, April
Sunlight

Preferred
Full Sun or Partial Shade

Exposure
Exposed or Sheltered

Size

Height
1 – 2M

Spread
1 – 1.5M

Bloom Time
July / August

Soil

Preferred
Chalk, loam, sand

Moisture
Moist but well drained

pH
Any

Phormiums are two species of herbaceous perennial, grass-like plant, which make a dramatic statement in a garden.

Though usually used solely as an ornamental plant in the UK, in other areas their long leaf fibres have been used as an economic fibre. In their native range in New Zealand they are known as ‘New Zealand Flax’, and the plants were widely used for textiles by Maori people and by early settlers.

What are Phormiums?

Phormium tenax in a garden with shrubs in the background
Phormium tenax

Phormiums are Phormium tenax and Phormium colensoi. To the Maori people, these are called, respectively, harakeke and wharariki. Though called ‘flax’, they are not closely connected to Linum usitatissimum, the plant known as flax in the northern hemisphere.

Both of these Phormium species, and the cultivars derived from them, are now widely grown as garden plants in many of the world’s temperate regions. And to a lesser extent, they are also still used for fibre production.

Why Grow Phormiums?

Phormiums are prized as ornamentals for garden use. These are large and dramatic structural plants which are valued for their striking long and pointed leaves, and the tall flower stems with yellow/green or muted red flowers born on mature plants in summer. The sharp leaves bend down to create domes of arching foliage. These leaves are often striped or tinged with shades of cream, yellow, red or pink along their margins.

Phormiums are drought tolerant once established, and are good for coastal gardens. They have no appeal for deer and rabbits, so can be used in gardens where these grazers are a problem.

Choosing Phormiums

Phormium 'Yellow Wave'
Phormium ‘Yellow Wave’

There are a lot of cultivars derived from Phormium tenax and Phormium colensoi. The RHS has given an Award of Garden Merit to:

  • Phormium tenax ‘Variegatum’ – green leaves striped with cream near the edges, reddish flowers.
  • Phormium tenax ‘Purpureum’ – green/dull copperish/purplish leaves, reddish flowers.
  • P. ‘Duet’ – green leaves variagated with cream towards the edges.
  • P. ‘Sundowner’ – rusty /green leaves with reddish pink edges.
  • P. ‘Yellow Wave’ – leaves feature bright yellow stripes.
  • Phormium colensoi subsp. Hookeri ‘Cream Delight’ – leaves mostly cream with green edges.
  • and ‘Tricolor’ – yellow/green striped leaves, edged with reddish pink.

So these varieties could all be considered.

As well as looking at the leaf colours and forms for the plants, it is also important, when choosing a Phormium, to think about size. The Phormium tenax and ‘Sundowner’ for example are taller specimens, which can reach over 2m in height. While others are much more compact and diminutive, some just over a 1m or a little more in height.

Another thing to bear in mind is that some Phormiums are hardier than others. Some are borderline hardy, and will suffer damage in winter where temperatures fall below minus 5 degrees C. Others, such as ‘Purpureum’ can cope with minus 10 degrees or even lower temperatures than that.

Where to Plant Phormiums

Phormiums need a location in full sun, sheltered from prevailing winds. In colder parts of the UK they will need to be grown in a particularly sheltered spot – against a south facing fence or wall, for example. In some colder areas, they may still need some winter protection.

The soil or growing medium in which they are planted must be evenly moist yet free draining. These plants will not well tolerate waterlogged conditions, and do not like spending the winter in wet conditions. They are often ideal for a gravel garden, or for a large statement container.

Where planted in heavier or less ideal soils, the area should be improved with plenty of good quality organic matter prior to planting.

When growing in a container, potting up should be carried out in spring. Try to maintain growing medium of 5cm around each side of the rootball. Ultimately, cultivars growing up to around 1.5m in height should be happy in a container around 50cm deep and 50cm wide. Bigger specimens will need larger containers however, or they may be prone to toppling over in windy conditions.

The RHS recommends that phormiums are grown in a peat-free multipurpose compost, with added John Innes potting compost. And that around 10% by volume of perlite or fine grit is added to improve the drainage in a container.

Whether you grow these plants in the ground, or in containers, make sure they have sufficient space, and will not grow to crowd out other plants close by.

stone planter on gravel containing Phormium 'Cream Delight'
Container with Phormium ‘Cream Delight’

When To Plant Phormiums

Container grown phormiums are available to purchase year-round. However, the best time to plant these is in the spring, after risk of hard frosts has passed in your area. When planted fairly early in the year, the plants will have time over the summer to become established before colder and wetter weather arrives in autumn and winter.

Be sure to plant the phormium to the same level in the soil or container that it was at in the pot in which it came.

Caring For Phormiums

Watering

Phormiums should be watered regularly over the summer during dry spells in their first year after planting. However, once established, these plants can be pretty drought tolerant, and will need watering only during very hot weather, or longer dry spells. Of course, plants in containers will need to be watered more regularly, and will be more prone to drought damage.

Feeding

When you are growing your Phormiums in the ground, it can be beneficial to add a multi-purpose organic fertiliser such as blood, fish and bone to the area after spring planting. Plants struggling with establishment may benefit from a mulch of compost or well-rotted manure. However, mature ground-growing Phormiums should not usually require feeding on an ongoing basis.

Phormiums in containers will thrive if provided with an organic liquid plant feed from late spring through to the middle of the summer.

Winter Care

As mentioned above, Phormiums growing in colder areas, and in particularly cold winters, may need some protection against the cold.

Mulching is not just for adding fertility. A thick dry mulch of straw or bark applied in winter can help protect the base of the plant. This should be laid around 10cm thick in autumn, before the first frosts, then removed in spring.

In colder parts of the British Isles, it may also be necessary to wrap the top growth with fleece or scrap fabric if a hard frost is forecast.

By far the most common problem people will encounter when growing Phormiums in the UK is damage due to hard frosts in winter. A plant can usually recover if only a few leaves have been damaged by winter cold. But if the damage has been more severe, the plants may be slow to recover, or may not recover at all. Keep the plant as healthy as possible and make sure it is in the best possible location to reduce the chances that something will go wrong.

Spring Tidy-Up

Phormiums do not need regular pruning. But older clumps will appreciate a spring tidy-up. Simply remove any old, damaged leaves. Pull or cut them off the plant as close to the base as you can. Cut out old flower stems too – as low down as you can without doing any damage to surrounding foliage.

If the clumps have become too large, do not heavily prune. Instead, you can consider lifting and dividing the mature plant.

Getting New Specimens From an Existing Plant

Division, carried out in spring, is not just for the purpose of reducing overcrowding, It is also the easiest way to obtain new Phormium plants. Leaf fans, complete with roots, can be potted up and grown on. Larger divisions can simply be placed right away into a different part of the garden.

Growing phormiums from seed is not for the novice. It poses something of a challenge. However, if you would like to give it a try, you can collect ripe seed and sow it in a propagator, at 18 degrees C., in spring. Be warned, however, the seed may grow into a plant that differs considerably from the parent plant. And you will have to be patient, since germination of these seeds can take up to a year!

Most gardeners will simply purchase these interesting and exotic looking plants, rather than going to the hassle of trying to propagate Phormiums themselves from seed. Fortunately, once you have one healthy mature specimen, division provides an easy way to increase your plant stock.

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