<em>Polystichum</em>: planting, cultivation and care

Description and botany

Polystichum are ferns that bear handsome evergreen fronds, dark green in colour, often twice divided. They are perennial and comprise around 276 species, plus hybrids. They have a very wide global distribution (Asia, Americas, Africa, Europe…). Greatest diversity is in Asia, notably China, although many species also come from North America. They are terrestrial or saxicolous plants, so grow on soil or on rocks. In nature, they are generally found in understorey on fertile, fresh, acidic or neutral soils, sometimes in scree, among rock outcrops, or along stream banks. But they are also prized in gardens for their ornamental value. One of the commonly planted species for this purpose is Polystichum setiferum. Polystichum tsus-simense is sometimes grown as an indoor plant.

Polystichum belongs to family Dryopteridaceae, which gathers more than 1,800 species. This is same family as Dryopteris, another fern occasionally cultivated for ornament and found wild in France.

Polystichum aculeatum: botanical illustration

Name of Polystichum derives from Greek polys (many) and stikhos (row), referring to rows of sori under fronds. Specific name P. setiferum means “bearing bristles” (seta: bristle, fero: to bear), referring to scales on petiole and rachis. In French, common names are Aspidie or Polystic.

Polystichum forms a crown of spreading fronds, which develop from an erect or slightly running rootstock. They measure between 40 cm and 1.20 m in height. Largest species include Polystichum setiferum and Polystichum munitum, while smallest include Polystichum acrostichoides, P. rigens and P. tsus-simense, reaching only 40–50 cm.

Polystichum does not produce flowers or seeds, but reproduces by producing spores. On underside of leaves, ferns produce tiny spores contained in “sacs” called sporangia, which are grouped into sori. When sporangia reach ripeness, they open to release spores, like dust, which are carried by wind.

In Polystichum, sori are rounded and covered by a small membrane called an indusium, circular in shape (a useful feature to distinguish Polystichum from other ferns such as Dryopteris, which have kidney-shaped indusia).

To reproduce, Polystichum need water. When spores fall to ground they germinate to produce tiny organisms (prothalli) that produce male and female gametes: these can meet and fertilise thanks to water. A new small fern will then develop directly from a prothallus.

Although more technical than sowing seeds, it is possible to sow Polystichum spores to obtain new ferns!

On underside of fronds, ferns produce spores grouped into masses called sori. Here, Polystichum × arendsii (photo Erwin Gruber) and Polystichum acrostichoides (photo Krzysztof Ziarnek)

When they appear, fronds are first coiled as croziers, forming a handsome spiral, covered with brown scales. In Polystichum, croziers tend to curve backwards. They then unfurl to reveal superb, delicate, finely cut fronds. Fronds are fairly dark, deep green (young fronds often paler, sometimes yellow-green) and generally glossy. They are thick, leathery, sometimes with a slightly rough texture. Fronds are borne on a petiole that continues into a central axis called rachis, around which pinnae unfold. Petiole and rachis bear scales, usually brown. Fronds are generally divided twice: they are described as bipinnate. They divide into pinnae, which themselves divide into pinnules. Pinnules are pointed and asymmetrical, generally auriculate (with an appendix). This helps distinguish Polystichum from other ferns such as Dryopteris, whose segments are rather symmetrical.

Some species, such as Polystichum acrostichoides and Polystichum munitum, have much less divided fronds, cut only once. Pinnae are entire, lobed, arranged on each side of rachis (central axis continuing petiole). They resemble fronds of Polypodium.

In Polystichum setiferum ‘Plumosum Densum’, fronds have a feathery, very soft appearance while remaining quite dense and compact. This variety provides an attractive textural effect in the garden!

Polystichum setiferum ‘Proliferum’ produces bulblets: these are like baby ferns that grow along central vein (rachis) of fronds. On contact with soil they can root and produce new ferns.

Fronds of Polystichum have advantage of being evergreen: they persist through winter! This fern therefore brings interest to garden year-round.

Young croziers of Polystichum setiferum ‘Pulcherrimum Bevis’ (photo Dominicus Johannes Bergsma), and fronds of Polystichum tsus-simense (photo David J. Stang), Polystichum setiferum (photo Christian Guthier), and Polystichum munitum (photo Jami Dwyer)

Main varieties of Polystichum

Most popular varieties

Our favourite varieties

Other varieties to discover

Polystichum polyblepharum - Japanese Lace Fern

Also called Japanese Aspidie, this fern bears arching, graceful fronds of a beautiful glossy green. The petiole and the frond's central axis are covered with brown scales. It tolerates heavy, clay soils.

• Height at maturity 60 cm

See the product sheet

Polystichum setiferum - Soft Shield Fern

This fern, also called Polystichum with bristles or Aspidie with stiff bristles, forms an elegant clump of very divided, evergreen fronds of matt green colour. The petiole and the rachis (central axis) bear brown scales. It was awarded the Award of Garden Merit by the Royal Horticultural Society (RHS).

• Height at maturity 60 cm

See the product sheet

Polystichum acrostichoides - Christmas Fern

Also known as the Christmas Fern, its fronds are evergreen and remain decorative even in mid-winter! These glossy green fronds are once-divided, with fairly broad entire pinnae forming lobes. It tolerates dry soils!

• Height at maturity 40 cm

See the product sheet

Polystichum munitum - Giant Holly Fern

This fern resembles Polystichum acrostichoides in the shape of its fronds, but is much larger! Moreover, its lobes are elongated and narrower than those of P. acrostichoides. It forms a handsome erect, spreading clump and can tolerate sunny positions!

• Flowering time February
• Height at maturity 1,10 m

See the product sheet

Polystichum setiferum Plumosum Densum - Soft Shield Fern

This variety offers dense, feathery foliage that adds volume to a border. It bears superb soft green, very divided fronds, creating a very interesting textural effect in the garden!

• Height at maturity 50 cm

See the product sheet

Polystichum setiferum Proliferum - Soft Shield Fern

This fern bears fronds divided into fine segments, giving them a soft, feathery appearance. It has the particularity of bearing bulblets along the main vein (rachis).

• Height at maturity 60 cm

See the product sheet

 

Polystichum tsus-simense - Korean Rock Fern

This is a small Polystichum that bears fine, slender, very architectural fronds. They are dark glossy green, with pinnae ending in points. It is suitable for growing in pots or containers, and can also find a place in a shaded rockery.

• Height at maturity 40 cm

See the product sheet

Polystichum setiferum Dahlem - Soft Shield Fern

This variety produces upright fronds, light green when young, later becoming dark green. It is slightly shorter than the type species Polystichum setiferum. As with variety 'Proliferum', its fronds bear bulblets.

• Height at maturity 80 cm

See the product sheet

Polystichum rigens - Rigid Holly Fern

This fern forms a small clump with evergreen, dark green fronds of slender, pointed shape... which makes it particularly architectural! Moreover, the young fronds have a lovely yellow-green tint.

• Height at maturity 40 cm

See the product sheet

Planting

Where to plant?

As Polystichum grows naturally in forest, in garden it will thrive in shade or partial shade. It can even tolerate quite dense shade. Don’t hesitate to site it in an understorey garden: its spreading fronds with a natural look make a lovely effect alongside other perennials, creating a lush forest atmosphere. Polystichum generally prefers rather humid conditions, except in winter.

Polystichum will do well in cool, light soil rich in humus. Before planting and during culture, we recommend adding well-rotted compost to enrich soil and improve its structure. However, Polystichum dislikes excessive winter moisture, so it is best planted in draining soil. It also prefers neutral to slightly acidic soils. Finally, you can quite happily use Polystichum in a shaded rockery.

However, some species can adapt to different growing conditions, since Polystichum acrostichoides seems to tolerate dry soils, and Polystichum munitum can withstand sun.

When to plant?

We recommend planting Polystichum in spring (around April) or in autumn (September to November), when temperatures are mild: avoid planting during frosts or extreme heat.

How to plant?

Don’t hesitate to plant Polystichum in groups rather than alone, to achieve an attractive massing effect! You can also pair it with other ferns to create a fresh, lush feel.

For planting in the ground:

1. Place the rootball in a tub of water.
2. Choose a suitable site, then dig a planting hole about twice the size of the rootball.
3. Place some well-rotted compost at the bottom, mixing it with garden soil.
4. Set your fern into the planting hole.
5. Fill the planting hole by replacing soil around the fern with a mixture of soil and well-rotted compost.
6. Water generously.
7. We recommend applying mulch around the clump so the soil stays cool for longer. You can use, for example, ramial chipped wood, pine bark or dried fronds.

For planting in a pot:

1. Choose a large pot or trough. It should have drainage holes in the bottom to prevent waterlogging and root rot.
2. Place a drainage layer of clay balls or gravel.
3. Put potting compost into the pot, possibly mixed with heather soil.
4. Plant the Polystichum.
5. Replace substrate around it and firm lightly.
6. Water thoroughly.
7. You can also add a surface layer of mulch for appearance and to help keep the soil cool.

Place the pot in a shaded spot and continue to water regularly.

Polystichum polyblepharum (photo: harum.koh)

Care

Polystichum, like most ferns, requires very little maintenance. It will, however, appreciate being watered during prolonged dry spells. If you grow it in a pot, remember to water it regularly throughout the year. Don’t hesitate to lay a layer of organic mulch around the clump, whether your Polystichum is planted in the ground or in a pot. This will help keep the growing medium cooler for longer, while enriching it and limiting weed growth. We also recommend, in late winter, removing dry and damaged fronds.

If you grow it in a pot, remember to repot it from time to time. Each time choose a pot slightly larger than the previous one. Or, if your Polystichum is already in a large pot, simply top-dress by removing a small layer of substrate from the surface to a depth of a few centimetres and replacing it with fresh potting compost.

Polystichum can be attacked by a fungal disease, Taphrina wettsteiniana. This fungus forms rounded, thick brown galls on the fronds, measuring up to 8 mm long. It is favoured by winter moisture, which is why we advise growing Polystichum in a well-draining substrate or protecting it from excess moisture in winter.

Multiplication

Sowing spores

Although Polystichum does not produce seeds, it is possible to sow spores. It is a delicate operation, but you can succeed if you provide suitable conditions, notably a sterile, moist substrate and a confined environment.

1. Harvest spores from Polystichum.
2. Take a transparent container, made of plastic or glass.
3. Put potting compost in it and moisten it.
4. Place the container in the microwave for about 10 minutes to sterilise it.
5. Wait for the substrate to cool, then sow Polystichum spores. Try to distribute them evenly over the surface of the substrate, but do not cover them!
6. Close the container with a clean, sterile transparent lid.
7. Place the sowing in a bright spot out of direct sunlight. Ideally at a temperature between 15 and 18 °C.
8. When young ferns appear, you can open the container and water if necessary.
9. You can then pot them on once they are large enough to handle.

For more information on sowing fern spores, see our advice sheet!

Dividing rootstocks

You can divide Polystichum rootstocks in spring.

Start by choosing a mature, vigorous clump. Lift it by digging fairly wide all around. Remove excess soil. Then cut the rootstock into several pieces with a sharp knife. Ensure each piece has fronds and roots to allow establishment. Replant each piece immediately, in ground or in a pot, then water generously.

Collecting bulblets

Some varieties, such as Polystichum setiferum ‘Proliferum’ or Polystichum setiferum ‘Dahlem’, produce small bulblets on their fronds, which appear along the rachis (central axis). These are baby ferns borne directly on the foliage and can produce new plants when placed in soil. Bulblets are collected in autumn.

To do this, start by preparing a pot with light, free-draining potting compost and water it to moisten. Cut the frond section bearing the bulblets, then lay it on the substrate. Bury the base of the bulblets very slightly. Place the pot in a bright spot out of direct sunlight, and ensure the substrate remains slightly moist by watering regularly.

Pairing Polystichum with garden plants

Like many ferns, Polystichum is ideal in a woodland garden. Indeed, it thrives in shade and grows naturally in forests. You can recreate a very natural atmosphere by combining it, for example, with Geranium nodosum, Solomon’s seal, Brunnera, Paris polyphylla, Hosta… Also enjoy the delicate yellow flowering of Erythronium ‘Pagoda’! You can also include some grasses, such as Luzula sylvatica. As groundcover, enjoy remarkable Cornus canadensis, which has superb whorled leaves and elegant flowers made up of four white bracts.

Polystichum is ideal in a woodland garden, with other plants that enjoy cool, shaded situations! Here, Galium odoratum (photo David J. Stang), Polygonatum multiflorum (photo Radio Tonreg), Polystichum braunii, Pachysandra terminalis ‘Cutleaf’ (photo Krzysztof Ziarnek), Geranium nodosum ‘Le Clos du Coudray’, and Cornus canadensis (photo Brian Gratwicke)

Also don’t hesitate to pair Polystichum with other ferns! We particularly recommend Dryopteris erythrosora, which bears superb coppery fronds in spring. Also discover Athyrium niponicum ‘Pictum’, with silvery–purple fronds, as well as Onoclea sensibilis, which forms genuine tapetum of fronds in bright hues, usually green–yellow, sometimes reddish. All these ferns have fairly similar growing conditions: they will enjoy shade, on fresh, light and humus-bearing soil.

Polystichum will also find a place in a modern, graphic garden. For example, you can plant it in a pot and place it in a patio or urban garden. You can then pair it with horsetails, bamboos, Ophiopogon, Hakonechloa macra, Stipa pennata… For flowering, choose, for example, white agapanthus, Alliums, or Gaura lindheimeri. We recommend favouring fairly restrained colours: white, black, purple, chocolate… to achieve a chic, streamlined garden!