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( Originally Published 1907 )
Although many of native ferns are eminently cosmopolitan, the successful cultivation of a goodly number depends largely upon simulation of natural environment.
Glancing over the list of species at our disposal we are surprised at the number which the mind instantly associates with rocks. Rocks not only by river and roadside, but in Nature's laboratory, where the choicest of fern treasures are scattered about on open or shaded ledges. This association of rock and fern is not accidental, but a simple device of Nature for inducing a lower temperature, moisture for the fern roots, and the needful supply of disintegrating limestone or other mineral matter.
The owners of large estates may be fortunate enough to possess a naturally shaded dell, or at least a ravine which can, with little expense and trouble, be converted into a charming glade, full of nooks and corners, where hardy ferns from all parts of the earth may be naturalised. The value of such a collection needs no comment.
Rockwork plays an important part in the landscape gardener's art. But great undertakings which require skilled artisans, an endless amount of stone and much expense are confined chiefly to public parks and gardens. Boulders artistically arranged about a fountain, with a leafy canopy overhead, are for the favoured few; but a few stones judiciously placed are within the reach of the majority and will afford more pleasure in proportion to the time consumed in the making and in space occupied than could be obtained in any other way.
A shady nook is of course the ideal location, but is not always available. Partial shade, however, is imperative. Pines and spruces make an artistic background and soften the abrupt transition from smooth lawn to ragged rocks. The colour effect of rock and fern against a screen of Virginia creeper (Ampelopsis quinque folia) is particularly fine, and within the reach of all.
THE BEST KIND OF ROCK
In the selection of rocks most people have to take what they can get; but, given a choice, sandstone and calcareous rocks are the most desirable. Much of the so-called artificial rockwork is composed of tufa, a soft, porous volcanic stone of light weight.
Nothing, however, can surpass the picturesque quality of a bit of old limestone in process of decay. Freshly quarried stones of any kind should never be used; the more rugged and weather-beaten they are the better for the place assigned.
Now and then one sees a giant pebble or cobblestone landed high and dry on a sunny lawn; just a bald, impenetrable, inorganic mass, without a depression, scam or furrow in which plant life of any kind could gain a foothold. Indeed, one might as well attempt to grow hair on an eggshell as to make even Boston ivy (Ampelopsis tricuspidata) cover the glaring surface. Obviously there are rocks and rocks. Those which are absolutely of no use and have no beauty are out of place on any lawn.
SOILS FOR ROCK PLANTS
Rock plants in general require light, sandy soil mixed with old mortar, if decomposed limestone is not at hand; brick rubbish also makes a satisfactory mixture. Certain species require a richer and lighter compost in which leaf-mould predominates.
BUILDING ON LAWNS
In building rockeries on our lawns we may follow general principles but may not imitate Nature in detail of construction, for too much confusion is out of place on a well-ordered lawn; therefore we have recourse to something "'twixt Art and Nature." Happily the stone-wall abominations, with dry, cramped pockets in which no respectable fern would attempt to grow, are things of the past.
The more exposed the position, however, the greater the need of something approaching regularity, in outline at least, for proper deference must be paid to the lawn mower. It is wise also to consider the feelings of the trimmer, else something besides grass will be cut off with the shears.
Whatever form of architecture is adopted, see to it that there is a soil connection through every pocket and crevice with the earth beneath, and that the top soil is firmed down to that which is underneath, otherwise capillary attraction will have no more chance of keeping the earth damp than in an imperfectly drained flower pot. This is the fundamental principle on which depends successful garden rockwork or rockeries.
Environments usually suggest the proper style, which should always be simple and unpretentious.
THE CIRCULAR ROCKERY A CONVENIENCE
As a matter of convenience, I have a circular rockery on my lawn. Careful selection of stone gives a varied outline; a curved slab of calcareous rock is highly valued, as it is so advanced in decay that layers are easily sprung and ferns inserted as fancy dictates. Regularity ceases with the marginal tier of stones. Four good-sized rocks artistically irregular in shape are placed at right angles slightly inclined toward the centre; the space between the big stones is walled up to a height of two or more feet, with a six-inch wall across the open front. This gives four large receptacles below the central pocket, with a twelve-inch border and no end of tiny nooks for tucking in petite members of the fern family.
Unless a rockery is in a sheltered nook the height should be limited to two and a half feet. No great expectations need be indulged in even at this low point, for none of our regal beauties that would answer for a centrepiece can endure the winds if thus elevated and isolated.
I had in my mind's eye an elegant vaselike ostrich fern (Matteuccia), which should crown my rockery with dignity and grace. My aspirations, however, were blown away, for no sooner did a frond unroll its curly tips than a wind promptly snapped the brittle stalk, and an inglorious and untidy "study in ferns" marred an otherwise successful creation. The plant was eventually removed, but stolons had penetrated in all directions and a fringe of young ostrich ferns appeared just below the summit; a beautiful wild aster volunteered inside the circle. Thus did Nature artistically adjust my failure.
THE BEST FERNS FOR ROCKERIES
Large clumps of osmundas and Dryopteris Goldieana were literally built into the four sections described. Lower down in the border are specimens of the maidenhair. The dark, glossy fronds of the Christmas fern (Polystichum acrostichoides) are largely in evidence, contrasting well with the reliable marginal shield fern (Dryopteris marginalis); both in turn foil the more delicately cut and coloured spinulose shield fern (D. spinulosa), with its varieties. The most distinguished member of the polystichum group is Braun's holly fern (P. Braunii).
Fine clumps of the purple cliff brake (Pelleea atropurpurea) are apparently as much at home as they are among the outcropping ledges at the base of scraggy cliffs, whence spores have doubtless been wafted from their inaccessible ancestry above. This fern is interesting and valuable; it is not only beautiful in design but unique in colour, a dark blue-green emphasising all the varying tints about it. It begins to unfold its fronds late in comparison with others, a desirable habit, as the oak fern (Phegopteris Dryopteris) is so intensely brilliant earlier in the season that nobody looks at anything else.
The beech fern (Phegopteris polypodioides), on the contrary, appears late in the season and keeps so fresh and looks so cool long after other deciduous ferns are fading that no rockery can afford to be without it. It is virtually a rejuvenator of its environment.
The common polypody is perhaps equally meritorious and should be lavishly used in rockwork. Of the smaller spleenworts, the ebony spleenwort (A. platyneuron) stands here as elsewhere like a small sentinel. Pretty rosettes of the maidenhair spleenwort (A. Trichomanes) are cropping out here and there, and tucked down in a shady corner is the green spleenwort (Asplenium viride). To the casual observer these two are much alike. Eaton (in Gray's Manual) limits the fronds of A. Trichomanes to from three to eight inches; those of A. viride to from two to six; the stipe and rachis of the former are black and shining, while those of A. viride are pale green; the former likes the sun, but the latter thrives only in the shade.
Very unlike any other of its genus is the wall rue (Asplenium ruta-muraria), the shy cliff dweller with sea-green fronds, which is as much at home in a rockery on the lawn as the walking leaf (Camptosorus rhizophyllus), which fastens its tapering points on every side. The pretty little rusty woodsia (W. Ilvensis) is excellent for rockwork, requiring little soil and thriving best in the sunniest corner. There is no mistaking this, for rusty indeed it is in dry weather, but it freshens up in a shower. The obtuse woodsia (Woodsia obtusa) requires more shade. Nearly all of the genus are cultivable.
Nature is over lavish with her favourite pattern of lacework, as seen in the bulbiferous bladder fern (Filix bulbi fera), graceful and fragile looking, yet the first to fling a mantle of green over rock and stone, and, as a natural sequence, the first to pass. The only remedy for this is to break away the old fronds in midsummer. This species reproduces itself in two ways: by spores and by bulblets located on the under side of the fronds; the latter start to grow so quickly after they fall that the species may become a nuisance, crowding out others equally desirable. The aftermath, however, is a compensation, for a second fragile mantle of green covers the trail of Jack Frost with fresh promise of the coming spring.
The hairy-lip fern (Cheilanthes lanosa), an attractive little Southerner which superficially resembles the rusty woodsia (X. Ilvensis), is one of the very best ferns for the lawn rockery. Growing naturally on the crest of rocks, it accepts trying situations with a better grace than many transplanted Northern species. In my own experience it is perfectly hardy, looking remarkably fresh after the severest Vermont winter on record. A light covering, however, is to be recommended for exposed situations.
No rockery is complete without the hart's tongue (Phyllitis Scolopendrium), the long, glossy, undulating fronds of which are sufficiently unique to distinguish any collection. The species is easily cultivated, but also needs light protection through the winter in northern New England.
FLOWERS ON THE ROCKS
Hepaticas, violets white and blue, may bloom among the ferns; even the rock-loving columbine loses none of its loveliness in its adopted home; but the ideal accessory of ferns in the rock garden are the harebells. Such strength and delicacy are not elsewhere found in the floral world. Like a rare trait in a rough character, they grace the rugged rocks on which they grow. Just a foothold and a chance to swing and sway as the breezes come and go are all that this flower of the air demands.
A clover-leaf design may be outlined in stone and a more artistic rockery constructed than the circular affair described. The letter S is also effective in rockwork. All of these designs are especially suited for exposed situations on the lawn. Location should always be considered, for the most picturesque of rocks may be piled the wrong, way for the place assigned, and detract from rather than add beauty to otherwise harmonious surroundings.
MAKING AND SHADING THE ROCKERY
In building rockwork it matters little what sort of earth is used for the foundation; but if taken from a rubbish heap it must be freed from vegetable matter, which may decompose and eventually cause the earth to settle away from the stonework.
In the construction of small rockeries of the style described, part of the ground tier of stones may be laid and the filling piled high in the centre, and either tamped or thoroughly wet down with the hose before the inside stones are placed.
A shady corner allures the fern grower, and affords scope for bewildering confusion of rocks and ferns or an artistical sectional arrangement, as fancy dictates. The latter is much more satisfactory in every way and may be as picturesque and informal as the material will admit or the ingenuity of the builder suggest.
MAKING SHADE WITH VINES
In the absence of shrubbery or trees, a shaded retreat could be affected with the vine alone. An odd lot of calcareous sand, rock and pudding stone compose the larger part of the rockwork. These stones look as if they might wash away, but, having withstood the elements for some fifteen years, they are not likely to vanish in the near future.
They are, however, sufficiently disintegrated to make the limestone with which they are impregnated available for the cliff dwellers to be grown thereon. A few other conglomerates, chiefly limestone and quartz, are in the foreground.
INSURING PLENTY OF MOISTURE
This was an especially dry corner, as the trees and shrubbery absorbed the natural moisture from the soil. For this reason, after the ground was cleared the hose was turned on and the water allowed to play for many hours before any filling was piled on. This in turn was wet down in instalments. Evaporation was thus checked and the soil thoroughly settled.
To insure a good slope of the side slabs, which diverge from a beautiful central upright, the earth was piled much higher in the rear and sloped toward the open front.
Some foundation stones were laid beneath the main divisions and cement used in a few of the points. Wherever this was used it was immediately dusted over with coarse sand and pebbles inserted to match the conglomerates.
Experienced handling is imperative, as the stones, so replete in tufts and turrets, are easily injured by small breakages, which lessen their artistic value. Careful selection and grouping of material are also necessary, for there is great difference in colour and wave of sandstone; an equally beautiful stone may look like a new patch on an old garment and spoil an otherwise harmonious whole.
Nature is so lavish of material that it is not difficult to blend one neutral tint into another, thus avoiding abrupt transitions which are so detrimental to any colour scheme. Space is left for massing tall ferns outside the walls. The large pockets are of course designed for vigorous growers. This wonderful formation is full of tiny grottoes, snug retreats and alluring nooks for the long list of dainty ferns which Nature tucks away in sheltered niches amid the ruins of the foreworld.
Although it is designed to make this rock garden a repository for a botanical collection, no attempt will be made toward grouping genera and species, since artistic value is not a secondary consideration. Only single specimens of the larger ferns will be admitted, but the lesser growths will be largely in evidence.
Space is left outside the walls for massing the common bracken or brake (Pteridium aquilinum), ostrich fern (Matteuccia Struthiopteris) and the interrupted fern (Osmunda Claytoniana). The tall fronds arching over the fawn-coloured stones will exquisitely frame the picture in the near future.
The royal fern (Osmunda spectabilis) is an admirable queen for the central pocket; maids of honour will be selected for contrasting beauty, and placed with reference to colour and design of foliage.
These rocks are so unique and beautiful in themselves that special care will be taken not to overload in stocking and to prevent the ultimate growth from hiding the formation of the rockwork.