How to Build a Rock Garden for Ferns

Building a Rock Garden for Ferns

When building a rock garden or rock wall, I usually leave a few vertical gaps an inch or so wide between the rocks, filling up the bottom few inches with well-fitting stones and mixture, pressed firm. Then a layer of mixture in which the fern roots are spread, covered, and then a few more tight-fitting stones, when perhaps another fern, and so on up to the top of the crevice. The Spleenworts remain green most of the year.

fern rock garden At the base of the rocks the dwarfer varieties of the Lady Fern look well on the flat, especially on the shadier sides of the rocks. Such varieties as Athyrium filix-femina minutissimum, which is a true miniature of the typical Lady Fern, four to five inches high, always attract comment. Other dwarf ‘Ladies’ are Athyrium filix-femina congestum in several forms, and Athyrium filix-femina crispum, all seldom exceeding six inches.

Athyrium filix-femina frizelliae, especially in its crested variety, looks fine spraying out from some vertical crevice, showing its remarkable fronds to better advantage than if it is planted on level ground. The Soft Shield Fern, Polystichum setiferum, has one or two varieties dwarf enough for the rock garden, and being evergreen is a great advantage. Polystichum setiferum Congestum and its crested form are excellent, while Polystichum setiferum Confluens is a finely cut, graceful variety seldom exceeding twelve inches.

Of the Male Ferns, Dryopteris filix-mas congesta cristata is excellent, with rather glossy, richly crested fronds, and Dryopteris filix-mas Linearis congesta is charming, finely cut, and does not exceed six inches.

In crevices or on the level nothing could be more cheerful than the green of the Harstongues, Phyllitis scolopendrium, in the dwarfer varieties P.s. Cristatum and P.s. Laceratum. These provide low mounds of glossy vivid green attractive foliage all the year round; their fresh greenery is doubly attractive on some dismal November day when all the rock plants have retired for the winter.

All the above-mentioned varieties are tolerant of lime, but in the lime-free garden there are additional species which can be tried. There is the Parsley Fern, Cryptogramma crispa, which, though deciduous, makes masses of finely cut foliage of a delightful shade of green, well worth the trouble of meeting its special needs. Although it is not easy to get established in ordinary garden soil, I have succeeded in persuading it to flourish by planting it in leafmould and peat, liberally mixed with lime-free grit and granite chippings, topdressing annually with the same mixture before the new fronds appear. Oak leafmould is the best to use for this fern.

The Hard Fern, Blechnum spicant, is perhaps a little large for most rock gardens, but the dwarfer B.s. Imbricatum sometimes is available and is a neat compact plant, also evergreen. It appreciates a perpetually moist position, and must have this if it is to attain its full stature, but it will stand a limited period of drought.

Of exotic ferns the New Zealand Blechnum penna marina makes a close bronzy-green evergreen carpet, some three to four inches high, spreading by runners just below the surface.

Then there are one or two Maidenhairs which can be used, particularly the dwarf montane forms of Adiantum pedatum and A. p. aleuticum, the latter seldom exceeding four inches. Their delicate-looking foliage is surprisingly tough, and they are very hardy. Adiantum venustum, too, seems to be quite hardy here, and I have seen it doing well in a cold Yorkshire garden. This has fronds more on the lines of the greenhouse Maidenhair, a lovely tender green in spring, sometimes with a glaucous sheen, and the foliage remains colourful until well into the new year if given some shelter. The dead fronds too are a warm russet shade, quite colourful in the late winter.

All the above ferns are the better for some shade and are therefore very useful in the shadier parts of the rock garden.

Cyclamen coum Associated with the ferns such beautiful things as the hardy cyclamens do very well; their corms are ripened during the summer more thoroughly by the fern roots drawing away excess moisture, and their flowers appear during the autumn and early spring. Such species as Cyclamen coum and its white and rose forms, C. cilicicum, C. atkinsii in white and rose, C. europaeum in autumn, sweetly fragrant, and C. neapolitanum and its pure white form all are thriving on my Polypody wall.

The hepaticas too are useful early spring-flowering plants which harmonize well with ferns. Ramondas and haberleas thrive in the shady vertical crevices; their evergreen foliage contrasts well with the more delicate fern fronds.

It is by no means a bad idea to construct a rock garden specially for ferns in some shady corner or near trees where conditions are too difficult for the sun-loving rock plants. To make such a rock garden the first requisite is to ensure good drainage, and usually this can be achieved by excavating the ground to a depth of a foot or so, putting the soil to one side. Fill up the hole with clinkers, old bricks, waste stone or other hard material right up to the original ground-level. Cover this drainage with a thick layer of old leaves, rough fibrous peat or other open material three to four inches thick, to prevent the upper finer soil from washing down and clogging the drainage material.

Now incorporate with the excavated soil, some good leafmould, fibrous peat, broken stone or crushed brick and coarse river sand in more or less equal parts to create a light spongy medium which contains plenty of humus, but which drains readily. Throw back this mixture over the filled-in areas, making irregular mounds ready to take the rocks.

When placing rock, it is just as well to make a good job of it and make something of a garden picture. Select a few of the boldest pieces and put them on one side for building up the dominant feature of the design. Starting with the smaller pieces, fit them together in an irregular outline, bedding them firmly, setting them so that they slope into the mounds at the same angle throughout, to give the impression that the tops of large rocks are just appearing above the surface, parts of one large outcrop. Break the irregular line here and there for soil to slope down to the ground-level.

Now build up a second series of shelving outcrops to form beds of varying size and leaving some joints open for vertical planting.

Use the larger rocks for the upper works, placing one dominant mass of the larger rocks previously selected in such a position that it forms a culminating point of the design, supported by the subsidiary outcrops, the latter complementing but not competing with the principal feature.

Outcrops need not be joined together right through the design; for valleys between the outcrops provide just the positions where some species thrive best.


09. May 2011 by Dave Pinkney
Categories: Ferns, Rockery Garden | Tags: , | Comments Off on How to Build a Rock Garden for Ferns


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