How to grow Phormium
Phormiums are undemanding exotic-looking, evergreens with eye-catching coloured, sword-like leaves. They are ideal for sunny borders, gravel gardens or containers. Their dramatic, curious flowers that tower over mature clumps in summer are a real talking point.
- Brightly coloured or variegated leaves
- Heights range from under 1m (3⅓ft) to 2.4m (8ft)
- Good for coastal planting
- Prefers full sun
- Plant in spring or early autumn
- Drought tolerant once established
- In cold areas protect the base by mulching
- Not palatable to deer and rabbits
All you need to know
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.
Though most are hardy in average UK winters, mulching 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.
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. Alhough they could 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, so 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 parts of country, 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
Though drought tolerant when established, phormiums prefer evenly moist soils. Improve the soil in planting area by digging in bulky organic matter such as garden compost or a manure-based soil conditioner. Add bucketful per sq m (yd).
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 like phormiums.
Phormiums in containers
The striking foliage makes phormiums 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
- 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 with added John Innes potting compost. Mix in perlite or fine horticultural grit to improve drainage, about 10% by volume
- Over time, the clumps may become congested and then they benefit from dividing in spring. See the Propagation below
- Water newly-planted phormiums during the first year after planting in the ground during dry spells, especially in summer
- Established plants usually cope well with drought, but some watering can be beneficial during very hot and dry weather if the plants are not growing well
- Container-grown phormiums are more vulnerable to drought damage. Water pots regularly, aiming to keep the compost moist, but not soggy
- For plants in the ground, apply a general fertiliser such as Vitax Q4, Growmore or fish blood and bone after planting in spring according to the manufacturer's instructions
- If struggling to establish or if the plants were damaged by a harsh winter, try feeding and mulching with organic matter such as garden compost or manure-based soil conditioner to encourage new growth
- Mature plants seldom need regular feeding, only if the growth is poor
- Container-grown plants benefit from regular feeding from late spring to mid-summer using a liquid feed. Alternatively incorporate slow-release fertiliser granules into the top layer of compost in spring to provide food for the whole season
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 such as bark, removing in spring
- In cold areas, consider wrapping the top growth with fleece if prolonged hard frost is forecast
- Move container-grown plants to more protected position such as close to the house wall
Phormiums are evergreen perennials so they do not 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 by hand wearing gloves 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.
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. Just lightly cover the seed with compost/vermiculite and keep at 18°C (64°F) in a propagator or airing cupboard
- Germination can take up to a year
Our guide below takes you step-by-step through collecting, storing and sowing seeds.
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. Follow by feeding with general fertiliser such as Growmore to encourage new growth. The recovery may be slow
- Give protection during the winter, consider mulching and wrapping to prevent future damage
- Consider moving the plant into a better-suited spot where is sheltered from hard frost and cold winds
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.
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