Name: New Zealand flax, flax lily, Phormium tenax, Phormium cookianum, Phormium hybrids.
Height: usually 0.3–3m.
Foliage: long, strap-shaped fibrous leaves, usually weeping at the tips, forming a fan-shaped clump of green, striped or multi-coloured foliage.
Climate: grows naturally in temperate regions with regular rainfall.
Soil: a moisture-retentive humus-rich soil is required.
Position: full sun to partial shade in warmer temperate climates. Many will grow partially submerged in ponds or water features, particularly P. cookianum hybrids.
Flowering and fruiting: panicles of nectar-producing flowers are carried on stiff upright stems high above the foliage, branching at sharp right angles. Decorative glossy seed pods are then produced.
Feeding: use a controlled-release organic fertiliser in early spring, and then regular liquid or granular fertilisers throughout spring, summer and early autumn.
Watering: regular watering 2–3 times per week is required throughout the spring and summer months. Plants will thrive in permanently moist conditions.
Flax plants feature imposing clumps of vertical arching leaves that grow up to 3m high in multicoloured and striped combinations of green, bronze, yellow, pink, white, orange, brown, red and purple. Sturdy branching stems of flowers rise well above the leaves, carrying many upright curved yellow-green or red-brown flowers dripping in bird-attracting nectar, followed by glossy black seed heads. The leaves are traditionally used to make rope, mats, baskets and textiles, and the seed heads used for decorative crafts.
The natural habitat of flax is restricted to New Zealand and Norfolk Island, within a range of habitat types including lowland swamps, mountain slopes and coastal cliffs in temperate and sub-tropical regions.
Flax will grow in most temperate climates with adequate summer rainfall and/or additional watering. In cooler climates it prefers to be planted in full sun, but partial shade is required for some of the P. cookianum hybrids to avoid foliage burn in warmer areas. Flax can be used to provide a focal point, foliage contrast and texture in tropical, coastal and mixed style planting schemes in both large and small gardens. It makes an impressive pot or container specimen, and is ideally adapted to pond and waterside planting. Phormium tenax provides an effective windbreak in coastal areas.
Flax grows best in a moisture-retentive or permanently moist soil, with a pH around 6.5–7. Mix in some compost or organic matter before planting. Flax will thrive in waterlogged conditions, or partially submerged in pots in either ponds or water features in warmer climates. In very cold climates, waterlogging may cause rotting of the stems in winter. Phormium tenax and its hybrids are more drought tolerant and adaptable to drier soils, although they grow naturally in wetlands in New Zealand.
In pots and containers always use a premium potting mix and keep the plant well watered throughout the warmer months.
Use a controlled-release organic fertiliser around the plant in spring. Granular or liquid fertilisers should be regularly applied from spring until autumn to encourage vigorous healthy foliage and flowers.
Flax can be affected by several different pests, but is usually trouble-free in most home gardens. Look out for caterpillars that eat the undersides or edges of the leaves, usually under the cover of night. Mealy bugs and scale may be found on the leaf blades, or near the ground where the leaves overlap each other. If these pests become problematic, insecticides can be used to control them. Slugs and snails can cause damage in moist environments, particularly for the smaller flax cultivars. These can be controlled using iron chelate-based snail pellets.
Fungal infections can affect the leaves, but in most cases removing the infected leaves and spraying the plant with a copper-based fungicide will control the problem. Yellow leaf disease is a serious disease caused by phytoplasma bacteria, which is transmitted by a native plant hopper in New Zealand. Afflicted plants exhibit stunted growth, unusual yellowing of the leaves, leaf collapse and crown rot, taking from a few months to a couple of years to progress. Dig up and burn infected plants to reduce the chance of the disease spreading further.
Flax is usually propagated by carefully dividing the crown in early spring. Dig up the clump and carefully pull it apart. Each fan of leaves with roots can be treated as an individual plant. Cut the leaves in half, or close to the ground, to reduce transpiration and to aid stability. Coloured-leaved or named varieties will only come true to type this way.
The seed of flax should be sown during autumn, as soon as the seed is ripe, with germination taking 1–6 months. Cover the seed and store at 18–21°C.
Canna: striking perennial producing colourful and luxuriant foliage with tall spikes of lily-like flowers during the warmer months.
Indian hawthorn (Raphiolepis): a tough and drought-resistant shrub with stunning white or pink flowers in spring.
Frangipani (Plumeria): a large deciduous and evergreen tree with exotic, sweet-smelling flowers and fleshy branches, perfect for growing in warm or tropical climate gardens.
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