How to grow Phormium

Choosing phormiums

Phormiums are mainly chosen for their height and leaf colour. There are forms with upright growing habit such as Phormium 'Sundowner' and Phormium tenax Purpureum Group that will reach over 2m (6⅔ft) in height, which you can plant at the back of a border. Others such as Phormium 'Jester' and 'Platt's Black' have more arching leaves growing around 1.2m (4ft) and work well as border highlights or as container plants. They all form slowly spreading clumps, making them a great choice for gravel gardens and focal point planting.

Hardiness

Though most are hardy in average UK winters, mulching

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. and wrapping may be needed to prevent winter damage during cold winters and in northern parts of the UK. Check the hardiness of your plant on the label as some are borderline hardy, such as Phormium ‘Duet', and can suffer when the temperature drops below -5°C; others such Phormium tenax Purpureum Group can withstand temperatures of -10°C or more.

Buying phormiums

Container-grown plants are available to buy all year round. Check the label for height and spread to make sure it is suitable for intended spot in your garden. Although they can be sold as small plants, phormiums can grow into a sizeable clump in just a few years.

The National Trust's Mount Stewart Garden in Northern Ireland holds the National Collection of Phormium and is a good garden to browse for inspiration.

Use our handy Find a Plant tool to find suppliers.

When to plant

As phormiums are not fully hardy, the best time to plant is in spring so the plants have time to establish well before the weather turns cold and wet. Planting during the summer and early autumn is also possible, but late plantings are more prone to winter cold and wet damage.

Where to plant

Bear the following in mind when choosing a site for your plant:

• Phormiums are well suited to a sunny border, sheltered from prevailing cold winds
• In colder areas, grow in a sheltered spot, for example close to south-facing wall or fence
• Plant in soil that is not prone to staying wet over winter
• Check the height and spread of the chosen plant to make sure it is suitable for the situation you have in mind
• Allow plenty of free space around them to stop phormium leaves smothering other plants

How to plant

Do not be tempted to plant phormiums deeper to help protect the base from frost damage. Plant at the same level as it is growing in the container.

Our guide below takes you step-by-step through planting perennials

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs. like phormiums.

Perennials: planting

Phormiums in containers

The striking foliage makesphormiums a great structural, focal-point plant for containers.

• When potting up in spring, increase the size of the container gradually each year by up to 5cm (2in) all round the rootball
  The roots and accompanying soil when a plant is removed from a container or lifted from the ground.
• Aim for a final size container of about 45-50cm (18-20in) cm deep and wide. This will be sufficient for cultivars growing up to 1.5m (5ft) in height. Larger cultivars are likely to need bigger container in time else they become top heavy and fall over in windy spells
• Grow in a peat free multi-purpose compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. with added John Innes potting compost. Mix in horticultural grit to improve drainage, about 10% by volume
• Over time, the clumps may become congested and can benefit from being divided in spring. See Propagation below

Perennials: dividing

Container maintenance

Watering

• Water newly-planted phormiums during the first year after planting in the ground during dry spells, especially in summer
• Established plants
  Established plants have been in their current location for two or three years and so have well-developed root systems able to support strong growth with healthy foliage and flowers. usually cope well with drought and shouldn't need any additional water
• Container-grown phormiums are more vulnerable to drought damage. Water pots as needed, aiming to keep the compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. moist, but not soggy

Feeding

• Plants in the ground shouldn't need feeding
• Container-grown plants can benefit from feeding from late spring to mid-summer using an organic-based, balanced liquid fertiliser. Always follow the dosage instructions and frequency on the pack

Winter protection

Though phormiums are hardy in average winters, some protection may be needed.

• Protect the base by mulching with a 7.5-10cm (3-4in) layer of dry mulch
  Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. such as bark
  Bark is the outermost layer of woody plants (trees, shrubs and woody climbers). It is several cells thick and provides protection against physical damage, disease and environmental stresses. Bark comes in a wide variety of colours and patterns, and these can help gardeners when identifying plants. The fissures and crevices of bark on older plants also creates valuable habitat for many garden creatures as well as lichens and small plants. , removing in spring
• In cold areas, consider wrapping the top growth with biodegradable
  Anything that can be decomposed by fungi, bacteria and micro-organisms, so it doesn’t persist indefinitely in the environment. Biodegradable plastics are usually made from plants, such as bamboo, rather than fossil fuels. Ideally, products that claim to be biodegradable should break down quickly and leave nothing harmful behind. However, they may need specific conditions in order to biodegrade successfully or may produce greenhouse gases such as methane in the process. fleece
  A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops. or hessian if prolonged hard frost is forecast
• Move container-grown plants to more protected position such as close to the house wall

Overwintering tender plants: lifting or mulching

Overwintering tender plants: wrapping

Pruning

Phormiums are evergreen perennials

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs. so they don't need regular pruning, but older clumps benefit from a tidy-up in spring

• In spring remove old, withering or winter damaged leaves Try pulling them away by hand or cut off as close to the base as you can manage
• Whilst tidying up in spring, cut out the old flower stems as low down as possible without damaging the surrounding leaves
• Do not hard prune clumps, unless they sustained considerable winter damage. The recovery may be very slow
• If the clumps start becoming too large, instead of pruning, consider lifting and dividing in spring

Propagation by division

It is easy to propagate phormiums by dividing the clumps in spring. Separate the leaf fans with roots, pot them up and grow on. If dividing into larger sections, you can plant the divisions straight away into prepared soil.

Our guide below takes you step-by-step through dividing your phormiums.

Perennials: dividing

Growing phormiums from seed

If you would like a bit of a challenge, you can try growing phormiums from seed, however the resulting plants are likely to be different in shape and colour from the parent plant.

• Collect ripe seed and sow in spring, using peat-free seed compost
  Seed compost is a free-draining compost formulated for germinating seed. It often contains a mix of fine materials including sterilised loam, coir, coarse sand or grit. It contains low levels of nutrients, as high levels could damage seedlings. . Lightly cover the seed with compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. and keep at 18°C (64°F) in a propagator
  A propagator is a portable, lightweight structure usually plastic, with a vented or unvented lid to provide a humid, slightly warmer atmosphere. It is useful to help seeds germinate and root cuttings. It may have adjustable, thermostatic temperature control. or airing cupboard
• Germination
  Germination is the process by which a seed develops into a new plant. It starts with the seed coat absorbing water, expanding and splitting, which allows oxygen and water into the seed so its food reserves can be broken down and used by the embryo for growth. The first root (called the radicle) pushes into the soil to anchor the new plant in place and start absorbing water and nutrients. The first shoot (called the plumule) then grows upwards, out of the soil, towards the light. can take up to a year

Our guide below takes you step-by-step through collecting, storing and sowing seeds.

Seed: collecting and storing

Cold damage

Phormium can be damaged by hard frost during cold winters

• In spring, remove the worst cold-damaged leaves
• Prune the plants hard only if the leaves are severely damaged. The recovery may be slow
• Give protection during the winter, consider mulching and wrappingto prevent future damage
• Consider moving the plant into a better-suited spot where is sheltered from hard frost and cold winds

Phormium mealybug

Black deposits on the leaves (sooty mould) and presence of white fluffy deposits around the base of the leaf fans can be sign of Phormium mealybug.

Phormium mealybug