Western sword fern

Polystichum munitum

In other languages: Polystichum (Nederlands) · Polystichum (Français)

Polystichum munitum, the western sword fern, comes from western North America, from Alaska to California, where it is one of the commonest ferns in the moist coniferous forests. It is a robust, evergreen fern about 90 cm tall, forming a large, fountain-shaped clump of long, straight fronds. Each frond is once divided, with narrow, leathery, glossy dark green pinnae that look like little swords. In spring the young croziers are covered in silvery-brown scales. Gardeners value it because it stays green all year and, once established, also tolerates fairly dry shade under trees.

Updated on 9 October 2026

Light
Partial shade or shade
tolerates little sun
Moisture
Normal
no wet feet
Legal basis
Sand, loam or clay
acid to neutral
Hardiness
Fully hardy
down to -20 °C
Size
0.9 m
tall, 1 m wide

Key facts
Pruning months	March
Height	0.9 m
Native to Belgium	No, planted
Poisonous to people and pets	Not known to be poisonous

Identify

Western sword fern: how do you recognise it?

Habit: Large, fountain-shaped clump about 90 cm tall and 1 m wide, from one or a few crowns.
Fronds: Long and narrow, once divided, 60–90 cm long; the pinnae are lance-shaped, leathery and finely toothed.
Pinnae: At the base of each pinna there is a small upward-pointing lobe, like the hilt of a sword.
Colour: Glossy dark green all year round. The young croziers are covered in silvery-brown scales.
Spores: Round spore clusters in two rows under the frond, with a round membrane; ferns do not flower.

Plants: March–May and September–October · Pruning: March

In your garden

Why grow it?

Evergreen: a full clump of dark green fronds, even in the middle of winter.
Once established it tolerates fairly dry shade under trees, where many other ferns give up.
A large, graceful fountain of fronds that gives structure to a shade border or woodland garden.
Grows in sand, loam and clay, as long as the soil is rich in humus.
Does not spread: the clump slowly widens but stays in its place.
Little work: cutting off damaged fronds once a year is enough.

Western sword fern: where does it grow best?

Partial shade to shade; morning sun is fine, but fierce midday sun scorches the fronds.
Humus-rich, well-drained soil: sand, loam or clay, acid to neutral.
Normally moist. Once established it tolerates fairly dry shade; it dislikes wet, heavy soil.
Sheltered from drying east winds, which turn the evergreen fronds brown.
Allow 1 m per plant: the clump becomes wide.

Light: Partial shade and shade
Soil type: Sand, loam or clay
Acidity: Acid or neutral
Moisture: Normal
Size: 0.9 m tall, 1 m wide
Hardiness: Hardy (to -20 °C)

Goes well with

Hellebore: Flowers in late winter, around the time you cut off the old fern fronds.
Barrenwort: A low, evergreen ground cover that also tolerates dry shade.
Rock cranesbill: Scented leaves and pink flowers in May–June, tough in dry shade.
Ivy-leaved cyclamen: Small pink flowers in September and marbled leaves in winter, under trees in dry shade.
Hosta: Large, broad leaves as a calm contrast to the long, narrow fern fronds.

Maintenance

Western sword fern: when and how to plant it?

Plant in March–May and September–October.

Plant from March to May or in September–October, when the soil is neither frozen nor too dry.
Dig a hole twice as wide as the pot and work in a few spadefuls of leaf mould or well-rotted compost.
Set the plant at the same depth as before: the crown belongs at the surface, not below it.
Leave about 1 m between plants and firm the soil well.
Water thoroughly straight away and keep the soil moist in the first year, even if it will later have to cope with dry shade.
Spread a layer of leaf mould or wood chips around the plant, but not over the crown.

Care

Water: In the first year, water weekly in dry spells so that it roots in well. After that only in long dry periods.
Feeding: Little needed: in April a layer of leaf mould or well-rotted compost. No chemical fertiliser.
Mulching: Leave fallen tree leaves around the clump; this keeps the soil rich in humus and moist.
Old fronds: In March cut off damaged and brown fronds, before the new croziers unfurl.
In a pot: A large, heavy pot with humus-rich, free-draining compost. Do not let it dry out and repot every two to three years.

Tip: Water it faithfully in the first year and it will then cope with dry shade under trees. In March cut off only the damaged fronds, so the clump stays full in winter too.

Western sword fern: when to prune it?

Pruning months: March.

When: In March, before the new croziers unfurl. Otherwise this fern needs no pruning.

How:

Cut off brown, damaged and flattened fronds at the base; healthy green fronds can stay.
For a fresh-looking clump, cut off all the old fronds just above the crown every few years.
Work carefully around the scaly croziers in the centre: they are the new fronds.
Wear gloves: the fronds are stiff and their edges finely toothed.

Caution: Do not wait until late April: once the new fronds are out, it is easy to cut them off by mistake.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division: In March–April lift older clumps with several crowns and divide them with a sharp spade or saw, each piece with a crown and roots. Replant at once and water well.
Spores: In late summer lay a ripe frond on a sheet of paper and sow the released spores on sterile, moist compost under glass. Small ferns appear after a few months; it takes a few years to get a sizeable plant.

Western sword fern: how does it get through the winter?

Hardy to −20 °C.

Hardy to about −20 °C: no problem in most Belgian winters.
In a severe winter with dry east winds the fronds may turn brown, but the crown usually survives and regrows in spring.
Leave the old fronds until March: they protect the crown. In a severe winter, add extra leaves around the base.
In a pot: stand it against a sheltered wall and wrap it in hessian in frost, as roots in a pot freeze more quickly.

Diseases and pests

Crown rot: The crown turns brown and soft in wet, heavy soil. Plant in a well-drained spot and improve clay with compost and coarse sand.
Brown fronds: Brown, dry fronds after hard frost, drying wind or in fierce sun. Cut them off in March and provide shelter.
Drought in young plants: Limp, dried-up fronds in the first year. Water weekly until the plant has rooted in well.
Vine weevil: Mainly in pots, the grubs eat the roots and the plant wilts for no obvious reason. Check the root ball and use nematodes against the grubs in late summer.

Through the year

March: Cut off damaged fronds. Spread leaf mould.
April: The scaly croziers unfurl. Plant or divide.
May: Plant. Water young plants in dry spells.
June: Water in dry spells, especially in the first year.
July: Water in dry spells.
August: Collect ripe spores.
September: Plant. Collect ripe spores.
October: Plant. Leave fallen leaves around the clump.
December: The evergreen fronds give structure to the winter garden.

You and this species

Did you know?

At the base of each pinna there is a small lobe that makes it look like a sword with a hilt: hence the name ‘sword fern’.
‘Munitum’ is Latin for ‘armed’, which suits the sword-shaped, finely toothed pinnae.
In its homeland the fronds are picked as cut foliage for bouquets and flower arrangements.

Garden plants · All species