Architectural foliage
How to grow phormium (New Zealand flax)
Phormium tenax / P. cookianum
Plant phormium in April or May in full sun and free-draining soil. The plain green and bronze forms of Phormium tenax are tough in most of the UK and stand salt wind; the coloured and striped hybrids are less hardy and suffer in cold, wet winters, so give them shelter or a pot. Winter wet at the crown does more harm than cold alone, and feeding should be light.
- Hardiness
- Frost-hardy; variegated types tender in cold, wet winters
- Position
- Full sun
- Soil
- Fertile, free-draining; coastal-tolerant
- Ideal pH
- 6.0 to 7.5
- Water
- Low
- Feeding
- Light feeder
Sowing and planting phormium (New Zealand flax)
WhenPlant Apr to May; flowers Jul to Aug on mature plants; tidy Apr
Starting off
Plant pot-grown stock Apr to May so it roots before winter; it is never sold bare-root. Propagate by division in Apr, levering the clump apart with two forks and replanting fans with roots attached, each with 3 to 5 leaves cut back by half; coloured hybrids must be divided, as seed does not come true. P. tenax seed sown at 18°C in Mar germinates slowly and erratically, sometimes taking many months.
Spacing and planting
P. tenax reaches 2 to 3 m tall by 2 m wide with 4 m flower spikes; P. cookianum and most coloured hybrids ('Jester', 'Yellow Wave'; 'Sundowner' is taller, to 2 m) 1 to 1.5 m by 1 to 1.5 m; dwarf 'Bronze Baby' 60 cm. Plant 1 to 1.5 m apart, in a hole twice the pot width with grit on heavy soil and the crown level with the surface. The coloured hybrids are ideal in a 45 to 60 cm pot of loam-based compost with grit, which also lets them be moved to shelter.
Varieties worth growing
- Phormium tenax
- The plain grey-green species and the hardiest: 2 to 3 m of upright sword leaves for a windbreak, a seaside garden or a bold full stop.
- P. tenax Purpureum Group
- Bronze-purple leaves on a plant nearly as tough as the green species. The safe choice for colour in a cold garden.
- P. 'Yellow Wave'
- Arching yellow leaves edged green, about 1 m. One of the more dependable variegated hybrids, and it keeps its colour in light shade.
- P. 'Sundowner'
- Upright bronze-green leaves with wide pink and cream margins, to 2 m. Striking, but needs shelter and winter protection inland.
- P. 'Bronze Baby'
- A dwarf at about 60 cm with stiff bronze leaves; the easiest to keep in a pot long term and to move under cover.
Month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do. Keep fleece on coloured forms in freezing spells.
- February
Nothing to do. Leave frost-damaged leaves on for now.
- March
Sow P. tenax seed indoors at 18°C. Remove winter wrapping in mild weather at the end of the month.
- April
Tidy: cut dead and tattered leaves out at the base. Plant, divide and give a light feed.
- May
Last month to plant. Water new plants weekly in dry weather.
- June
Water pots. Check leaf bases for mealybug.
- July
Mature plants send up flower spikes. Water pots in hot spells.
- August
Flowering continues. No feeding from now on.
- September
Cut finished flower spikes at the base, or leave the seed pods for effect.
- October
Stand pots on feet. Move potted coloured hybrids to a sheltered wall.
- November
Mulch round the crown, not over it, with 10 cm of bark. Have fleece ready.
- December
Tie leaves up loosely and wrap coloured forms when below -5°C is forecast.
Feeding phormium (New Zealand flax)
A light feeder that gets by on almost nothing in the ground. One small balanced feed in April is the most it needs; more makes the leaves soft, floppy and less hardy. Never feed after midsummer.
Low, a light spring feed; over-feeding softens the leaves.
Feeding plan
April or May, at planting
Garden compost
A spadeful in the backfill on sandy soil; on heavy soil add grit instead. No fertiliser in the hole.
April, plants in the ground
50 g/m², half the label rate of 100 g/m²: one handful scattered round each plant and watered in. Once a year, and skip it on fertile soil.
April, pots
2 g per litre of compost, the bottom of the label range, on the surface and watered in: about 80 g for a 45 cm pot holding roughly 40 litres. Once.
May, after a hard winter
1 g per litre of water as a drench (10 g in a 10 litre can), weekly for 2 to 3 weeks to bring a frost-damaged plant round, then stop.
Signs to watch
Soft, floppy leaves that bend in the middle
Excess nitrogen or rich soil
No feeding, lean gritty ground, full sun
Coloured hybrids fading to green
Shade or reversion
Full sun, cut out green fans at the base
Older leaves yellow between the veins in a pot
Magnesium short
Epsom salts drench
Pests, diseases and problems
White waxy fluff deep in the folded leaf bases, leaves yellowing and dull
Phormium mealybug, which hides where sprays and predators cannot reach
Cut affected fans out at the base and bin them; a badly infested plant is best removed. Part the leaf bases and check before buying, as it nearly always arrives on new stock.
Leaves folded over, grey and mushy at the base after a hard frost
Frost damage, worst on coloured hybrids and in wet soil
Leave until April, then cut damaged leaves out at the base. Wait until June before digging up a plant that looks dead; new fans often come from the rhizome.
The centre of the fan rots and pulls out
Crown rot from water standing in the crown or at the roots over winter
Plant on a slight mound with grit on heavy soil, keep mulch off the crown itself, and stand pots on feet from October.
Brown or reddish spots and streaks on the leaves
Fungal leaf spot, encouraged by cold, wet weather and crowded fans
Cut marked leaves out at the base in April and thin old clumps by division so air moves through.
Leaf tips brown and split
Wind, or drought in a pot
Remove whole leaves at the base rather than trimming tips. Water pots through summer and move them out of wind tunnels between buildings.
Pruning
Pruning and care
Tidy in Apr by cutting dead and tattered outer leaves right out at the base with a sharp knife, never shortening live leaves, which leaves ugly brown tips; cut the flower spikes at the base after flowering in Sep. In cold, wet winters tie the leaves up loosely in a column and wrap the plant with fleece or hessian below −5°C, especially coloured and variegated types; mulch the crown 10 cm with bark
Good to knowBold evergreen sword leaves; remove tatty outer leaves at the base. Hardier in free-draining soil.
Growing in pots
The coloured hybrids are often better in a pot than in the ground, because the pot gives sharp drainage and can be moved. Use a 45 to 60 cm pot of loam-based compost with a quarter by volume of grit, in full sun. Water well in summer; phormiums in pots are thirstier than their leathery leaves suggest and the tips brown if they dry out. From October stand the pot on feet against a sheltered wall, and in a hard frost wrap the pot as well as the plant, since the roots are more exposed than they would be in the ground. Divide and repot in April when the fans press against the sides, usually every three to four years.
Common questions
Are phormiums hardy in the UK?
The green and bronze forms of Phormium tenax are hardy through most UK winters, taking roughly -10°C in well-drained soil. The pink, red and yellow striped hybrids are less tough and can be badly damaged below about -5°C, especially in wet ground. Inland and in the north, grow those in a sheltered spot or a pot and wrap them in hard frost.
How do you cut back a phormium that is too big?
Remove whole leaves and whole fans at the base in April; do not shorten the leaves, because cut ends stay brown and never regrow. To reduce the size of the clump properly, lift it in April and divide it, replanting a smaller piece. A phormium cannot be kept small by trimming, so choose a cultivar that fits the space.
Why are my phormium leaves drooping?
Frost damage is the commonest cause in spring: the leaves fold where the base has been frozen and they will not straighten. In summer, drooping usually means a dry pot, shade, or soft growth from too much feed. Cut folded leaves out at the base in April, water pots properly and keep feeding light.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.