Dwarf Ferns for Limited SpaceBy Todd Boland (Todd_Boland)
November 15, 2008
At some point many gardeners have to deal with shade issues. Shade need not be a detriment as many lovely ornamental plants are ideally suited to shade; hosta, astilbe, pulmonaria and primroses are just a few examples. If you have a small shaded area, a shaded planter or a shaded rockery, you now have a host of miniature hosta to choose from. But what to plant with them for some contrast? Ferns would seem a logical choice, but many of the popular cultivars are relatively large. As it happens, there are several ferns that mature under 30 cm (12 inches) and some that rarely exceed a few centimetres. This article will introduce you to some of these exquisite and often, underutilized or unknown dwarf ferns. While there are plenty of tropical and subtropical dwarf ferns, this article will deal with the hardier ones, suitable for zone 6 or colder.
For simplicity, I'll describe these ferns alphabetically, starting with Asplenium, the spleenwort ferns. This genus is quite large and occurs worldwide from the tropics to the Arctic. For gardeners, the easiest to grow is the beautiful maidenhair spleenwort, A. trichomanes. This species occurs throughout the northern hemisphere, often growing in shaded cracks in limestone. They form small, tufted plants with fronds 8 to 20 cm long. The pinnae are quite rounded and arranged as a double-row on either side of a contrasting black stipe. They remain green all year. Ideally suited to a shady rockery, rock wall or alpine trough, this tough little fern will survive as cold as zone 3. Looking very similar, but slightly more challenging to cultivate, is the green spleenwort, A. viride and the ebony spleenwort, A. platyneuron. The former is rated for zone 3 while the latter, zone 5.
Asplenium viride and A. trichomanes, growing in cultivation
From the farthest reaches of the southern hemisphere comes a lovely evergreen fern called Blechnum penna-marina. This creeping fern can spread fairly quickly making it suitable as a groundcover in semi-shaded areas. The new fronds emerge pink-tinted then mature dark green. The fronds are narrow and may reach 20 cm. It is rated for zone 5.
Blechnum penna-marina makes a lovely groundcover
The genus Cheilanthes include the lip ferns and cloak ferns. There are many which are under 30 cm. This genus mostly hails from desert regions! The fronds are greyish-green, somewhat thick and often fuzzy, adaptations to life in dry areas. These ferns can be difficult to cultivate in areas outside their native haunts. In the garden, they can tolerate considerable sun but must be planted where there is sharp drainage. Most are rated for zones 7 to 8 but C. lanosa and C. tomentosa, two tufted species, are rated for zone 5 and 6 respectively. Despite being hardy, they should still be protected from excess winter-wet. They are semi-evergreen.
Cheilanthes tomentosa growing in a 4 inch pot
Cryptogramma or rock-brake ferns, are very hardy species (zones 2 to 3) from northern North America and Eurasia. They look superficially like parsley, forming tufted plants 10 to 30 cm high. These evergreen ferns can tolerate considerable sun if the soil stays reasonably moist but normally they grow in shaded rock crevices. They resent hot temperatures thus are difficult to cultivate in most parts of North America. The species most likely to be encountered are C. stelleri, C. acrostichoides and C. crispa.
Cryptogramma crispa growing in the wild
Fragile fern, Cystopteris fragilis, and the closely related bulblet fern, C. bulbifera, are tough little ferns (zone 3) which, I think, are underutilized. They have very finely divided, lance-shaped fronds that are among the earliest ferns to show in the garden. Full shade to considerable sun are tolerated but these ferns do have a tendency to go dormant by mid-late summer. They are tufted species. There are several other species worth cultivating including C. montana, C. alpina, C. dickieana and C. tennesseensis. All Cystopteris benefit from additional lime in the soil.
Cystopteris fragilis in the wild and in the garden
There is only one wood fern that is small enough to be included among the miniature ferns and that is the fragrant wood fern, Dryopteris fragrans. This very hardy fern (zone 3) is quite tufted in habit, with narrow, lance-shaped fronds reaching about 15 cm. The foliage is fragrant when rubbed. Ideal for a shaded alpine trough or rockery.
Oak ferns, Gymnocarpium dryopteris and G. robertianum, are both delicate ferns which produce individual, triangular-shaped fronds from a running rhizome. Over time, they can make an admirable groundcover. Dappled to full shade and reasonable moisture will suit these hardy ferns (zone 3). While the former prefers slightly acidic soil, the latter prefers a limey soil. Both are deciduous species.
Gymnocarpium dryopteris growing in the wild
Cliff brake ferns, Pellaea, are closely related to and have similar growing requirements as Cheilanthes. Like Cheilanthes, many Pellaea hail from semi-desert regions and are difficult to cultivate outside their native range. The fronds are somewhat coarse, many being blue-green with contrasting black stipes. One of my favourite ferns, but difficult to grow if you cannot protect the crowns from winter-wet. The easiest and hardiest member is P. atropurpurea. Rated for zone 3, this semi-evergreen fern is a confirmed lime-lover. Part shade best but they have considerable tolerance to sun.
Pellaea atropurpurea, growing in the wild
Beech fern, Phegopteris connectilis, sits on the fence in regards to size. Some populations stay consistently small with somewhat triangular fronds 15-20 cm. Others are larger with fronds reaching to 45 cm. Plants produce a creeping rhizome but are relatively slow to spread.. Ideal on banks located in shade to semi-shade. They prefer moist, acidic soil and are super hardy, to zone 2. This species is winter deciduous.
Phegopteris connectilis in the wild and in the garden
While there are many rock polypody or Polypodium ferns, the two smallest ones are P. vulgare and P. virginianum. These two species look very similar but the former hails from Eurasia while the latter from North America. Both are rated for zone 3. These evergreen ferns have leathery, lance-shaped fronds and in the wild, often grow atop moss-covered rocks. They will tolerate full sun to shade but need a moist yet well-drained, acidic site. They send up individual fronds from a creeping rhizome but overall, the plants are relatively tufted in appearance. In milder zones you can try P. hesperium or P. interjectum. All of these perform best if planted in rocky crevices.
A collection of Polypodiums including P. virginiana, P. hesperium and P. interjectum
Among the evergreen holly ferns, the two smallest are Polystichum lonchitus (zone 3) and P. scopulinum (zone 5). These evergreen ferns have stiff, leathery fronds that are narrow and lance-shaped with overlapping pinnae. They are among the most beautiful of ferns. Part-shade with moist yet well-drained limey soil seems to suit them best. They dislike hot summers thus are most at home along coastal regions of the Pacific northwest or Atlantic Canada.
Polystichum lonchitus in the wild and in the garden
The New York fern, Thelypteris noveboracensis also sits on the fence in regards to size. But since they are relatively small and such a great fern for using as a groundcover, I thought I would include it. This deciduous fern has bright apple-green, feather-shaped fronds that arise individually from a narrow, creeping rhizome. Plants are relatively quick to spread, making this small fern one of the best ones to use as a groundcover in shady sites. Moist, acidic soil in dappled shade is their preference. This fern is hardy to zone 3.
New York ferns photographed in the wild
Finally we come to the genus Woodsia. There are many to choose from (if available!) and all stay under 30 cm. Some are evergreen while others are deciduous, but all are tufted in habit. Superficially, they look like fragile ferns, Cystopteris. They prefer semi-shade to full sun but need a moist site. They are not fussy about soil pH. The easiest to grow is W. obtusa (zone 3) but others worth trying include W. alpina (zone 2), W. glabella (zone 4), W. ilvensis (zone 3), W. scopulina (zone 3), W. polystichoides (zone 5) and W. intermedia (zone 5).
A collection of Woodsia including W. alpina, W. obtusa, W. glabella and W. ilvensis
These are but a few of the many miniature ferns that the ‘limited-space' gardener can cultivate. Whether in a rockery, an alpine trough, planted in a rock wall or grown as a groundcover, these small-sized ferns are a wonderful addition to our gardens.
I would like to thank the following people for the use of their pictures: kennedyh for Polystichum lonchitus, Polypodium hesperium and P. interjectum; cretaceous for Pellaea atropurpurea and growin for Blechnum penna-maria.