How to Grow and Care for New Zealand Flax

New Zealand flax

The Spruce / Letícia Almeida

Gardeners grow New Zealand flax (Phorium tenex) as a large and often colorful, spiky plant that makes an arresting focal point in the garden or containers. It has sword-like leaves that shoot up from the base of the plant. New cultivars and hybrids are available with foliage in bright shades of yellow, pink, red, and bronze.

These blade-leafed, evergreen perennials are often used as specimen plants. Some are small enough to use in containers, while others can reach several feet in diameter and grow to over seven feet tall. New Zealand flax is a rather slow-growing species that can take several years before small seedlings mature into full-sized plants.

On mature plants, the flower stalks shoot up above the leaves and produce curving, tubular red or yellow blossoms that are very high in nectar and are a hummingbird favorite. Seed pods form after the flowers bloom. The seed pods are attractive in their own right, but you should deadhead them if self-seeding is not desired.

Botanical Name Phormium tenax (P. colensoi is a second parent to some hybrids)
Common Name New Zealand flax
Family Asphodelaceae
Plant Type Herbaceous perennial
Mature Size 1-6 feet tall, 1-3 feet wide
Sun Exposure Full sun to partial shade
Soil Type Well-drained soil
Soil pH Acidic
Hardiness Zones 9-11 (USDA)
Native Area Australia
frontal view of New Zealand flax

The Spruce / Letícia Almeida

closeup of New Zealand flax

The Spruce / Letícia Almeida

base of New Zealand flax

The Spruce / Letícia Almeida

New Zealand flax used in landscaping

Ron Evans / Getty Images

New Zealand Flax Care

New Zealand grows in average, well-drained soil and a location sheltered from harsh winds. These plants will also tolerate poor, non-fertile soil. This plant is grown mostly for its attractive foliage, but it produces flower stalk with red or yellow flowers in mid-summer.

As with most perennials, spring is the traditional time to plant New Zealand flax. If you are dividing or transplanting it, make sure to do so before the plant begins to send up new growth shoots in the spring.

In climates above its cold hardiness range, is very common to grow these plants in large containers, moving them indoors for the winter. In the spring, the plants need to be gradually reacclimated before moving them back outdoors permanently for the summer.

Light

New Zealand flax prefers a full sun location but will tolerate partial shade. Because it is usually grown for its foliage, full sun is not crucial. In fact, in hotter climates, hybrids might do better with afternoon shade to enhance leaf color.

Soil

New Zealand flax is not fussy about soil; it will do well even in poor soil, provided it is well-drained. It prefers slightly acidic soil but is perfectly happy in neutral soil. When grown in containers, rich potting mix is preferred over standard potting mix.

Water

New Zealand flax has average water needs. When planted in the garden, about one inch of water per week in the form of rainfall and/or irrigation is ideal. Potted plants should be kept consistently moist, but not soggy.

Temperature and Humidity

New Zealand flax is dependably hardy and evergreen in USDA cold hardiness zones 9 to 11, but gardeners in zones 7 and 8 might find that the plants re-grow each spring after dying back if they are heavily mulched and protected for the winter. More often, cold-weather gardeners grow them as potted plants that are moved to an indoor shelter for the winter.

Fertilizer

These plants tolerate poor soil and thus don't usually require much in the way of feeding. An annual top-dressing of well-rotted compost can help provide nutrients and retain soil moisture.

Types of New England Flax

New varieties of Phormium are introduced just about every year and are becoming more and more ornamental. Take a look around your local nursery to see what they've introduced this year. Be aware that the cultivars and hybrids are sometimes more temperamental than the pure P. tenax species plant. Established favorites include:

  • Phormium tenax 'Bronze Baby' has bronze foliage and grows to about two feet tall with a two- to three-foot spread. It is a good choice for containers.
  • Phormium 'Duet' is a compact plant (about one foot tall). It has green leaves edged in cream, with very stiff leaf blades.
  • Phormium 'Jester' has bronze leaves with green striping. It is about three feet tall.
  • Phormium 'Sundowner' has green leaves with rosy-pink margins. It is about six feet tall and wide.

Pruning

The best time to prune New England flax is in the fall. Start by removing dead, dying, or diseased leaves. Cut them off at the base. Trim again in the spring if winter temperatures have killed or damaged any leaves. If it appears the entire plant has been destroyed by a cold snap, this might not be the case. Cut the plant down to the ground and give it some time; the roots might still be perfectly healthy.

Propagating New Zealand Flax

When grown in a garden setting, clumps of New Zealand flax can get quite large and overcrowded over time. Dividing them not only gives you a new plant for your own yard or to give away, it also tidies up an old plant. Here's how to do it:

  1. In the spring, lift the entire plant out of the ground with a shovel. If it is too big to move it in one piece, do it in sections.
  2. Shake off any excess soil, which helps to separate the clump into smaller sections.
  3. Cut down the leaves to about six inches with pruners or shears. This prevents the plants from toppling over when you replant them. 
  4. You can either replant each section in a new location right away, or start new plants by potting smaller pieces each in their own container with fresh potting mix, and allowing them to grow for a month or two before transplanting them into the garden.
  5. Keep the newly planted New Zealand flax well-watered until you see new growth.

How to Grow New Zealand Flax From Seed

New Zealand flax can also be started from seed, although it needs a warm temperature of over 60 degrees Fahrenheit to germinate. Sow the seeds in warm soil and water them well, then wait for the seedlings to arrive. When they do, thin them out to provide plenty of room to grow.

Potting and Repotting

Phormium tenax can easily be grown in containers. Choose a rich, organic mix over traditional potting soil and keep the plant well-watered in summer’s heat, but don't allow the plant to sit in wet soil for a prolonged period. Don’t allow the plants to experience frost. When wintered indoors, this plant prefers cool temperatures and lots of sunlight.

Overwintering

In its cold hardiness zones, overwintering is not an issue. Gardeners in zones 7 through 9 might find that their plants will die back with colder temperatures. Cover the bed with a heavy layer of mulch to protect the plant until it springs back in the warmer temps.

Common Pests and Plant Diseases

Mealybugs can infest plants and are hard to eradicate from inside the long leaves. Many times it’s easiest to just dispose of the infested plant. Fungal leaf spots may also mar the leaves.

When grown indoors, these plants are susceptible to many of the common pests affecting other houseplants, including mites and whiteflies. Horticultural soaps and oils are the first options for treating these pests.

FAQ
  • What is the difference between New England Flax and Lesser New England Flax?

    A closely related species that also goes by the common name New Zealand flax or lesser New Zealand flax is P. colensoi. This plant is less common than P. tenax, with shorter leaves that have a lesser degree of recurve. The seed pods are twisted and pendulous in shape. These species readily interbreed, and some of the named cultivars are crosses between the two species.

  • How big will a New Zealand flax get?

    The mature size of your New Zealand flax plant will depend on the variety and your growing conditions. Many plants in containers grow one to four feet tall, but Phormium tenax can reach ten feet under ideal conditions.

  • What is New Zealand flax famous for?

    Phormium tenex got the name New Zealand flax because the Maoris of New Zealand used it for making a type of linen clothing, similar to flax as well as for ropes and baskets.

  • What are good companion plants for New Zealand flax?

    Contrast Phormium's dramatic leaves with low-growing, delicate foliage such as perennial geraniums and coreopsis.