Gymnocarpium: Planting, Growing and Caring

Botany

Gymnocarpium comprises 9 species of charming small creeping ferns, with rootstocks, featuring delicate and finely divided, deciduous fronds. They grow in temperate and cold regions of the Northern Hemisphere: found in Northern and Central Europe, temperate Asia, North America, and as far as Greenland.

In France, we notably find Gymnocarpium dryopteris and Gymnocarpium robertianum. These are montane ferns, typically found in high-altitude forests, though they can also be encountered in lowlands (more rarely). They mainly grow above 500 metres in altitude, up to 2,300 metres. This explains why these ferns are very hardy: they can withstand temperatures as low as –25, even –30 °C. Gymnocarpium dryopteris grows on siliceous, acidic soils in forest floors, while Gymnocarpium robertianum is found on calcareous rubble, scree zones, cliffs and old walls.

Gymnocarpium belongs to the large group of ferns and horsetails, the Pteridophyta. These are primitive, very ancient plants that existed long before flowering plants appeared. Ferns, along with mosses, were among the first plants to emerge from water and colonise dry land. They retain a very primitive organisation in their tissues and mode of reproduction, remaining dependent on water for reproduction.

Gymnocarpium dryopteris: Botanical illustration

Among ferns, Gymnocarpium is related to the botanical family of Cystopteris (another charming small montane fern found in France), the Cystopteridaceae. This small family includes only three genera and 41 species of ferns.

The name Gymnocarpium comes from the Greek gymnos: “naked”, and karpos: “fruit”, referring to the absence of an indusium (a small membrane that usually covers the sori in ferns). The name dryopteris comes from the Greek drus: “oak”, and pteris: “fern”. In French, it is nicknamed the Oak Fern. However, it does not grow specifically near oaks but is rather found in beech and conifer undergrowth.

Gymnocarpium is a ground-covering fern, spreading gradually thanks to its creeping and ramified rootstock. Generally, it measures 20-30 cm tall (up to 40 cm maximum). Gymnocarpium dryopteris can form dense and extensive carpets.

The fronds are directly attached to the underground rootstock by their petiole. Thus, instead of forming a clump or crown like other ferns (for example Matteuccia or Dryopteris, where all fronds emerge from the same point), the fronds appear to emerge individually from the soil.

As with other ferns, the fronds first appear as spiralled croziers, then the lamina gradually unfurls.

The fronds are borne on a long, thin petiole, dark brown at the base, and longer than the lamina. The junction between the top of the petiole and the base of the lamina is jointed, allowing the fronds to orient themselves according to light. They are generally held horizontally.

Gymnocarpium is appreciated for its fronds of a beautiful soft green colour, finely divided, giving them a light and airy appearance, very delicate. With its fresh and luminous hue, this fern is perfect for bringing a bit of brightness under the canopy of large trees. The fronds have a very fine and light texture. They are two to three times divided (bi to tripinnatisect) and have a characteristic isosceles triangle shape. This is due to the two basal pinnae, which are almost as large as the rest of the frond. The fronds are glabrous, devoid of hairs. They measure between 10 and 20 cm long and wide.

The fronds of Gymnocarpium dryopteris and Gymnocarpium robertianum (photos: Radio Tonreg / Len Worthington)

The fronds of Gymnocarpium are deciduous. This fern unfurls its fronds in spring, produces spores in summer, then the fronds dry out in autumn… and reappear the following spring.

The two species Gymnocarpium robertianum and G. dryopteris are very similar, easily confused, but the former is distinguished by slightly pubescent petioles and rachises, a bit thicker, and more divided fronds, somewhat more tapered and elongated than those of G. dryopteris. The petioles and rachises of the latter are black and rather thin, very slender.

Like other ferns, Gymnocarpium does not produce flowers or seeds but multiplies by releasing spores, fine as dust. They are produced on the underside of the fronds in summer (between July and September). They are contained in small sacs (sporangia), grouped in rounded clusters (sori). Unlike other ferns, they are not covered by an indusium (protective membrane). These very light spores are released when they reach ripeness and dispersed by the wind. They will fall to the ground and germinate upon contact with water, giving rise to small intermediate organisms resembling moss: the prothalli. These bear the sexual organs. Water enables fertilisation, and they will then give rise to new young plants of Gymnocarpium in the form we know.

The spores of Gymnocarpium are contained in small sacs called sporangia, grouped in circular clusters on the underside of the fronds. Left photo shows those of Gymnocarpium robertianum, not yet ripe, and right photo shows those of Gymnocarpium dryopteris. Their black colour indicates they are ripe and ready to release spores. (photos: Krzysztof Ziarnek / Walter Siegmund)

The main varieties

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Planting

Where to plant?

Like most ferns, Gymnocarpium are woodland plants: they therefore thrive in shade (even deep shade). They need soil that remains moist, and appreciate a good humus-bearing and light soil, such as that found in woodland. Don’t hesitate to add well-rotted compost or manure to enrich the soil.

Be mindful of the pH as Gymnocarpium dryopteris prefers acidic soils, while Gymnocarpium robertianum has a preference for limestone! The former grows on the ground, on humus-bearing and moist terrain, while Gymnocarpium robertianum is found in the wild among rocks, in areas of rubble or scree, or on old walls. Thus, it will particularly enjoy a cool and shaded rockery.

As it is a small fern, we recommend planting Gymnocarpium in groups to achieve a beautiful effect more quickly. It will form a dense and spreading tapetum faster if you plant several young plants together.

When to plant?

Plant Gymnocarpium in spring, around April, or in autumn, in September-October.

How to plant?

1. Start by placing the pot in a basin filled with water to rehydrate the root ball.
2. Dig a planting hole, about three times the size of the root ball.
3. Place some soil mixed with well-rotted compost at the bottom.
4. Carefully remove the Gymnocarpium from its pot and place it in the centre.
5. Fill in around it with soil.
6. Gently firm with the palm of your hand to ensure good contact between the soil and the roots.
7. Water generously.
8. You can add a layer of mulch (dead leaves, dried fronds, wood chips…).

To learn more, feel free to consult our guide on planting ferns

Gymnocarpium dryopteris (photo Adobe Stock)

Maintenance

Like other ferns, Gymnocarpium requires little maintenance once established and is rarely affected by diseases or parasitic organisms. Especially in the first few years, ensure the soil remains moist by watering when necessary. For Gymnocarpium dryopteris, it’s best to use rainwater, as tap water might be too calcareous for it.

Don’t hesitate to apply a mulch of dead leaves, dried fronds or RCW (ramial chipped wood) around the base of the Gymnocarpium. As well as keeping the soil moist for longer, this mulch will suppress adventive growth and gradually enrich the soil as it decomposes. For more advice, see our dedicated mulching guide.

Similarly, as Gymnocarpium is deciduous, you can cut back the withered fronds in autumn.

Propagation

Sowing

It is possible to propagate Gymnocarpium by collecting the spores that detach from the underside of the fronds and sowing them. Gymnocarpium produce spores in summer, between July and September.

1. Start by mixing compost and sand, then sieve it to obtain a fine medium.
2. Place it in a transparent plastic or glass container.
3. Water to moisten the medium.
4. We recommend microwaving it (about 10 minutes) to sterilise it. This will prevent the appearance of mosses and fungi.
5. Wait for the medium to cool, then sow the spores by scattering them on the surface. Be careful, unlike traditional sowing, do not cover them with compost!
6. Then place a transparent lid on the container. This will keep the medium moist and sterile.
7. Place your sowing in a bright spot, out of direct sunlight, ideally at a temperature of 15 to 20 °C.

Division

As Gymnocarpium spreads via its creeping rootstocks, once well established it can be propagated by dividing its rootstocks in spring. This method is much easier and quicker than sowing spores.

1. Choose a well-developed clump of Gymnocarpium;
2. Dig it up carefully, making sure to dig wide enough to avoid damaging the rootstock and roots;
3. Remove excess soil to clearly expose the rootstock;
4. Cut it into several sections, each with a few fronds and roots;
5. Replant each section in the ground or in pots;
6. Water generously.

Association

With its very delicate fronds, the Gymnocarpium dryopteris will easily find its place in a naturalistic woodland garden. It will form large tapetums in the shade of trees, in companion with, for example, sweet woodruff. You can easily pair it with hostas, brunneras, Solomon’s seal, Geranium nodosum, masterworts… as well as with other ferns. Also consider the delicate flowering of Tricyrtis!

The Gymnocarpium dryopteris will beautifully accompany heather soil plants, which thrive like it in acidic soil. Consider, for example, rhododendrons and azaleas, Japanese maples, Andromeda polifolia, heathers, Skimmia japonica… Also integrate other ferns, such as Cyrtomiums or Blechnum spicant, which bears long dark green fronds.

Gymnocarpium integrates easily into a woodland garden with a very natural style! Geranium nodosum, Dodecatheon conjugens (photo C.T. Johansson), Hosta ‘June’, Gymnocarpium dryopteris (photo Len Worthington), Galium odoratum (photo Jack W.Pearce) and Blechnum spicant (photo brewbooks)

The Gymnocarpium robertianum, on the other hand, will be perfect in a cool, shady rockery. You can pair it with ferns such as Coniogramme emeiensis, Cyrtomium falcatum, polypody or hart’s tongue fern. Also consider Tiarella, coral bells, Ajuga reptans, dead-nettles, hostas and saxifrages. Discover our guide “10 plants for creating a shady rockery”

And for more pairing ideas with Gymnocarpium, feel free to consult our guide: “Ferns: 9 easy-to-achieve pairing ideas!”