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

Description and botany

Polystichum are ferns bearing handsome evergreen fronds, dark green in colour, often twice-divided. They are perennials, comprising around 276 species, together with hybrids. They have a very wide global distribution (Asia, Americas, Africa, Europe…). Greatest diversity is found 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 the wild, they are generally found in the understorey, on fertile, fresh soil, acidic or neutral, sometimes in scree, among rocky outcrops, or by stream edges. They are also ferns appreciated in gardens for their ornamental value. One of most commonly planted for this purpose is Polystichum setiferum. Polystichum tsus-simense is sometimes grown as houseplant.

Polystichum belongs to family Dryopteridaceae, which includes more than 1,800 species. This is same family as Dryopteris, another fern sometimes cultivated for ornamental interest and found wild in France.

Polystichum aculeatum: Botanical illustration

Name of Polystichum comes from Greek polys: many, and stikhos: row, alluding to rows of sori beneath fronds. Species name P. setiferum means “bearing bristles” (seta: bristle, fero: to bear), referring to scales on petiole and rachis. In French, these ferns are commonly called Aspidie or Polystic.

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

Polystichum do not produce flowers or seeds, but reproduce by releasing spores. On underside of leaves, ferns produce tiny spores contained in “sacs” called sporangia, which are grouped into sori. When they reach ripeness, sporangia open to release spores, resembling dust, which are dispersed by wind.

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

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

Although this process is 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 clusters called sori. Here, Polystichum × arendsii (photo Erwin Gruber) and Polystichum_acrostichoides (photo Krzysztof Ziarnek)

When they emerge, fronds are first coiled into croziers, forming a beautiful spiralled crozier covered in brown scales. In Polystichum, these croziers have the particularity of being curved backwards. They then unfurl to reveal superb fronds, delicate and finely divided. Fronds are rather dark, deep green (young fronds often take lighter, sometimes yellow‑green tones), generally shiny and lustrous. They are also thick, coriaceous, sometimes slightly rough in texture. Fronds are borne on a petiole that continues into a central rachis around which the pinnae unfold. Petiole and rachis bear scales, generally brown. Fronds are usually divided twice: they are bipinnate. They divide into pinnae, which in turn divide into pinnules. Pinnules are pointed and asymmetrical in shape, generally auriculate (with an appendix). This feature helps distinguish Polystichum from other ferns such as Dryopteris, which have rather symmetrical segments.

Some species, such as Polystichum acrostichoides and Polystichum munitum, have much less divided fronds, cut only once. Pinnae are entire, lobed, arranged either side of rachis. They resemble fronds of Polypodium.

In Polystichum setiferum ‘Plumosum Densum’, fronds have a feathery, very soft aspect while remaining fairly dense and compact. This variety brings an interesting textural effect to the garden!

Polystichum setiferum ‘Proliferum’ has the particularity of bearing bulblets: small baby ferns that grow along the midrib (rachis) of fronds. On contact with soil they can root and produce new ferns.

Fronds of Polystichum have the advantage of being evergreen: they remain in place even through winter. This fern therefore helps enliven garden throughout year.

Young croziers of a 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 Shield Fern, this fern bears arching, graceful fronds in a lovely glossy green. The petiole and central axis of the frond 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 silky Polystichum or ciliate shield fern, forms an elegant clump of very divided, evergreen fronds in matt green. The petiole and rachis (central axis) bear brown scales. It has been 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 Christmas fern, as 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

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Polystichum munitum - Giant Holly Fern

This fern resembles Polystichum acrostichoides in frond shape, but is much larger! In addition, its lobes are elongated, narrower than those of P. acrostichoides. It forms a handsome upright, spreading clump and tolerates 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 brings volume to a border. It bears beautiful soft-green, deeply 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 is notable for 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 with fine, elongate, very graphic fronds. They are dark glossy green, with pinnae ending in points. It is suitable for pot or container culture 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 erect fronds, light green when young then turning dark green. It is a little shorter than species-type 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 elongate, pointed habit... which makes it particularly graphic! In addition, young fronds have a lovely green–yellow hue.

• Height at maturity 40 cm

See the product sheet

Planting

Where to plant?

As Polystichum grows naturally in forest, in the garden it will thrive in shade or partial shade. It can tolerate quite dense shade. Feel free to site it in an understorey garden: its arching fronds with a natural habit will make a very attractive display alongside other perennials, creating a lush forest atmosphere. Polystichum generally favours fairly humid conditions, except in winter.

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

However, some species can adapt to different growing conditions: Polystichum acrostichoides appears to tolerate dry soils, and Polystichum munitum endures 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 periods of extreme heat.

How to plant?

Don’t hesitate to plant Polystichum in groups rather than singly to achieve a striking massing effect! You can also combine it with other ferns to create a cool, lush atmosphere.

For planting in the ground:

1. Place the rootball in a basin of water.
2. Choose a suitable location, 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. Put your fern into the planting hole.
5. Fill the planting hole with a mixture of soil and well-rotted compost around the fern.
6. Water generously.
7. We recommend applying a mulch around the clump to help keep soil 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 container. It must have drainage holes in the base to prevent water from stagnating and rotting roots.
2. Install a drainage layer consisting of clay balls or gravel.
3. Add potting compost to the pot, optionally mixed with heather soil.
4. Plant Polystichum.
5. Backfill with substrate around it, and firm lightly.
6. Water well.
7. You can also add a surface mulch for appearance and to help keep 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. However, it will appreciate being watered during prolonged drought. If you grow it in a pot, remember to water regularly throughout the year. Also consider applying a layer of organic mulch around the clump, whether your Polystichum is in the ground or in a pot. This will help keep the substrate cool for longer, while enriching it and limiting weed growth. We also recommend, at the end of winter, removing dry and damaged fronds.

If you grow it in a pot, remember to repot it occasionally. Each time choose a pot slightly larger than the previous one. Or, if your Polystichum is already in a large pot, simply carry out top-dressings by superficially removing a little substrate, a few centimetres, and replacing it with fresh potting compost.

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

Propagation

Sowing spores

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

1. Collect spores from Polystichum.
2. Take a transparent plastic or glass container.
3. Put potting compost into it and moisten.
4. Place container in microwave for about 10 minutes to sterilise.
5. Wait for the growing medium to cool, then sow Polystichum spores. Try to distribute them evenly over the surface of the growing medium, but do not cover them!
6. Close container with a clean, sterilised transparent lid.
7. Place your sowing in a bright spot out of direct sun. Ideally at a temperature between 15 and 18 °C.
8. When young ferns appear, you can open 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, discover our advice sheet !

Division of rootstocks

You can divide Polystichum rootstocks in spring.

Begin by choosing a vigorous, well-developed clump. Lift it by digging widely around it. Remove excess soil. You can then cut rootstock into several sections using a sharp knife. Ensure each section has fronds and roots to allow establishment. Replant each section immediately, in ground or in a pot, then water well.

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. Collecting bulblets is done in autumn.

To do this, prepare a pot with light, free-draining potting compost and water to moisten. Cut off the section of frond bearing bulblets, then lay it on the growing medium. Bury the base of the bulblets very slightly. Place pot in a bright position out of direct sun and keep growing medium slightly moist by watering regularly.

Companion planting with Polystichum in the garden

Like many ferns, Polystichum is ideal in a woodland garden. It thrives in shade and grows naturally in forests. You can recreate a very natural atmosphere by pairing it, for example, with Geranium nodosum, Solomon’s seal, Brunnera, Paris polyphylla, Hosta… Also discover the delicate yellow flowering of Erythronium ‘Pagoda’! You can also include some grasses, such as Luzula sylvatica. As a groundcover, enjoy the 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 like cool, shaded conditions! 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)

Feel free to pair Polystichum with other ferns! We particularly recommend Dryopteris erythrosora, which bears beautiful coppery fronds in spring. Also discover Athyrium niponicum ‘Pictum’, with silver–purplish fronds, as well as Onoclea sensibilis, which forms true tapetum of fronds in bright tones, generally green-yellow, sometimes reddish. All these ferns have fairly similar growing conditions: they will like shade, in fresh, light and humus-bearing soil.

Polystichum will also find its place in a modern, graphic garden. For example, 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-flowered agapanthus, Alliums, or Gaura lindheimeri. We recommend favouring fairly sober tones: white, black, purple, chocolate… to achieve a chic, pared-back garden!