Mountain flax

Sun

Full sun or partial shade; foliage colour is usually strongest in sun.

Water

Moderate; water regularly while establishing and during prolonged dry spells. Established plants tolerate some drought.

Soil

Fertile, moisture-retentive but well-drained soil; tolerates clay if drainage is adequate. Avoid stagnant, waterlogged ground.

Height

3-5 ft (0.9-1.5 m) in leaf; flower stems can reach 6-8 ft (1.8-2.4 m)

Spread

3-5 ft (0.9-1.5 m)

Flowers

Summer; yellow-green tubular flowers, sometimes tinged with red, on tall, branching stems. Flowering can be irregular in cool climates.

Foliage

Evergreen. Long, leathery, sword-shaped green leaves arranged in fans, with arching or drooping tips. Named garden selections may have coloured or striped foliage.

Growth

Moderate

Care needed

Low

• Pollinators
• Deer resistant
• Drought tolerant
• Heat tolerant
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Moderate

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   2 ft (0.6 m)

3. After 2 years

   3 ft (0.9 m)

4. After 3 years

   4 ft (1.2 m)

   full size

About 3 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Growth rate

Moderate

• Water deeply through the first growing season, allowing the soil surface to begin drying between waterings.
• Apply compost around the clump in spring; feed container plants lightly with a balanced fertiliser.
• Mulch around the roots, keeping mulch clear of the leaf bases.
• Use a sheltered position in colder districts and protect the crown with horticultural fleece during hard freezes.
• Grow in a large container with drainage holes where winters require moving it into a bright, frost-free place.

Pruning. In spring, cut dead or badly frost-damaged leaves individually at the base without cutting into healthy fans. Remove spent flower stems near ground level; do not shear across the foliage.

Spring

Remove dead leaves and assess frost damage once severe freezes have passed.

Spring

Plant or divide clumps, water thoroughly and apply a light compost mulch.

Late spring

Begin light feeding of container-grown plants.

Summer

Water new plants and containers during dry weather; check leaf bases for mealybugs.

Late summer

Cut out finished flower stems unless you want to keep the seed pods.

Late autumn

Move containers under cover where winters are cold and prepare frost protection for outdoor plants.

• Use a single clump as an architectural focal point beside a patio or entrance, leaving room for the arching leaves.
• Combine with ornamental grasses and rounded shrubs for contrasting shapes in a mixed border.
• Plant in coastal gardens with salt-tolerant shrubs, away from the harshest wind exposure.
• Grow in a large container to provide evergreen structure in a courtyard.

Garden styles it suits: Architectural minimal, Coastal, Modern, Modern courtyard, Pacific Northwest woodland and Winter interest.

Plant it with: Hebe, New Zealand sedge, Agapanthus, Lavender, Japanese silver grass and Pittosporum.

Wildlife: The nectar-rich flowers feed birds in its native New Zealand and may attract nectar-feeding birds where these occur. Insects also visit the flowers, although flowering is not dependable in every garden.

• Frost and cold winds can split, scorch or kill leaves; choose a sheltered site, protect during hard freezes and remove damaged leaves in spring.
• Phormium mealybugs hide between tightly packed leaf bases; inspect regularly, remove accessible colonies and use a locally approved treatment labelled for mealybugs if needed.
• Root or crown rot can develop in waterlogged soil; improve drainage, keep the crown at soil level and avoid leaving pots standing in water.
• Brown leaf tips can follow drought or drying winds; water deeply during prolonged dry weather and provide shelter rather than repeatedly trimming healthy leaves.

Not known to be toxic to people, cats, dogs or horses. It is not an edible plant; the tough, fibrous leaves can cause choking or digestive upset if chewed or swallowed.

• New Zealand flax (Phormium tenax)

  Usually larger and more upright, with stiffer leaves, predominantly reddish flowers and upright seed capsules; mountain flax has more arching leaves, yellow-green flowers and hanging, often twisted capsules.

• Cabbage tree (Cordyline australis)

  Eventually develops a woody trunk topped with leaf rosettes and bears sprays of small cream flowers; mountain flax remains a ground-level clump of leaf fans.

• Adam's needle (Yucca filamentosa)

  Has stiff, sharply pointed leaves with curling threads along their edges and large cream, bell-shaped flowers, rather than the softer arching fans and tubular flowers of mountain flax.

Phormium comes from the Greek word for a basket, referring to the useful leaf fibres, while cookianum honours Captain James Cook.

Propagation. Divide established clumps in spring, keeping roots and several healthy leaf fans on each division. Seed can be sown in spring, but seedlings from coloured or variegated selections may not resemble the parent.

Accepted botanical name

Phormium colensoi Phormium cookianum is an older name for Phormium colensoi.

Native range

New Zealand North and New Zealand South.

Sources: GBIF (CC BY 4.0) and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.