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Rock Garden Construction



The actual construction of the rock garden demands a lot of thought and care.

The wildness of Alpine plants, their freedom of growth, and the natural way in which they spring from the rock fissures, unfits them for association with plants of calmer habit.

The proximity of well graveled paths, of mown turf and trim borders, robs the rock garden of all its significance and charm, making it appear but an untidy heap of stones overgrown with straggling vegetation. Isolation, then, should be the first thought when planning an ideal home for rock plants and Alpines.


The worst positions would be found near walls, buildings and fences, which are as far as possible removed from the wild spirit of the mountain solitudes. Trees should not be found near the rock garden, not merely for aesthetic considerations, but because their roots, far reaching and greedy, will impoverish the soil.


Alpines, and indeed most rock plants, demand the fullest exposure to sun and air. The damp, still atmosphere which pre­vails in tree sheltered spots, is not conducive to their welfare.


When a pathway is cut through a high bank, as is often necessary in hill gardens, the steep sides may be prepared for planting by the use of stones to form rough walling.Rock Garden Plants


Many Alpines succeed better on these almost perpendicular faces than on level ground, and the walls are so constructed that they show no trace of mason's work, but resemble rather the sheer drop of a miniature cliff. Raised banks between two sections of the garden, natural knolls and wild craggy ground covered with furze and heather, suggest themselves as other spots offering inducements for conversion into rock gardens.


Where natural rock stratum exists a few inches below the soil, it will always be better to make the rock garden by excavation rather than by the addition of fresh stone work. In such cases the practice of employing artificial stone substitutes, when there is already a natural outcropping of rock in the ground is bound to be strongly marked.


If natural stone is unobtainable use the artificial substitute.


When starting the actual work of rock garden con­struction, one thought must be kept prominently in view - the requirements of plant life take precedence over considerations of the picturesque.


For this reason, it is the gardener, not the builder, who should arrange the disposition of the rocks. The rock garden is a home for plants, and the beauty afforded by the stones themselves, though not inconsiderable, is quite secondary.


Elevation in rock gardens should always be obtained by masses of earth, and not by stones piled one above the other, with soil in the crevices. The foundation of large banks may consist of brick ends, builders' rubbish, and any convenient material, but above this should be soil to the depth of at least two feet.


Too often we see flat rocks laid so as to form a series of ledges, or pinnacles in which each stone is carefully balanced on its predecessor. Handfuls of soil are crammed into any convenient crevice, and in such unpromising quarters plants are expected to grow. Naturally, as soon as the roots have pushed their way through the ball of soil, they are in a barren air­chamber, and during a dry summer half of them perish.

 Rock Garden

In the well built rock garden the soil is rammed firmly home, and no vacuum exists between adjacent stones. Rocks which are hollowed out on the under side must be sunk into loose soil, so that the cavity is completely filled. Unless the work is made firm in all its stages, the effect of frost and heavy rain will be to cause soil subsidence, leaving innumerable air spaces.


At this stage it is helpful to study rocks in their natural positions. An area of English moorland offers a striking object lesson in this respect. On level ground, smooth rocks, usually of fair size and round in shape, rise a few inches above the ling and heather. Occasion­ally we come upon a slight knoll or ridge, from which a cluster of lichen stained rocks thrust themselves boldly. The higher the ground, the more rocks, and vice versa. The fact is one which should be remembered in garden­ making of this description.


Always use the smooth flat stones for the lower levels, and be content with quite a few. Higher up the bank the plants will be smaller and the boulders more conspicuous, whilst at the top tufts of diminutive Saxifraga and Androsace will cling to the sides of the roughest and most weathered rocks. This is not an attempt to imitate Nature's methods, but it is adopted because in no other way do the various families of Alpine plants appear to so great advantage.


Stones should be laid in the earth with their broadest sides downwards, the bases should also be sunk in the soil. Lines of natural stratification should be simulated where possible, as this produces a more restful and coherent effect.


If the stones are of small size, and the rock garden slopes abruptly, it will be necessary to build an occasional course of dry-walling, otherwise the earth will slip forward after heavy rain. The walling must be built very carefully, as it is important that all trace of builder's work shall be concealed.


Choosing the largest stones available, a single course should be laid somewhere about the ground level. The earth must be well rammed, and the spaces between adjacent stones filled with soil.


A thick layer of soil is now placed above the stones, in the same way that mortar is spread between lines of bricks. A second course of stones is now put into position, no idea of uniformity in size being entertained. The dry-walling is carried up as far as necessary. In the case of almost perpendicular slopes, it will be convenient to make a series of ledges, as these permit freer planting, and serve to break the monotony.


When setting the stones, it is desirable that each should be placed so that it tilts slightly backwards, in other words, the front faces are not perpendicular. Not only does this serve to strengthen the wall, but the rain collecting in tiny runnels, soaks into the earth crevices and refreshes the plants. This rule holds good as regards the disposition of all stones and rocks in the Alpine garden.


These sections of dry-walling, which are necessary in nearly all rock gardens formed on banks, require to be closely planted. The joints and seams between the stones should be completely hidden by Saxifrages, Ferns, Alpine Primulas and various Sedums.


Then if the stones have been laid so that they simulate the lines of natural strata, the idea of a wall will give place to a solid, unbroken rock face, in the fissures of which various small plants have established themselves.


When build­ing, it is convenient to lay a wooden spline vertically against the front face of the rock wall from time to time. It will then be easy to ascertain if the centre stones are in a line with the rest, or are too much advanced. The latter is a serious error in rock build­ing, as sooner or later it leads to the bursting outward of the whole structure and the loss of many valuable plants.


Apart from considerations of economy, local stone should always be used, as being most likely to harmon­ise with the character of the surrounding vegetation. Sandstone blocks are extremely useful, this material having the additional advantage of weathering to a picturesque shade.Mountain Plants


Limestone is also good, but slaty, crumbling material is of little value, as it soon succumbs to the disintegrating influence of the atmosphere. On no account should gnarled tree roots, broken stumps or woodwork of any description be included in the rock garden.


The paths in the rock garden should be of the simplest description. They need never be of greater width than two persons walking side by side, whilst the smaller back paths should be capable of admitting one. A good effect will be obtained by sinking irregular stone slabs at intervals, much in the way that the native rock appears along the foot-worn track on mountain side or cliff path.


Flat stones by the path edge, with an occasional rock jutting out from the garden slopes, will help to disperse any appearance of formality. Coarse gray gravel and small stones will form the best surface, and provide a dry, clean footway in all weathers.


There are many small plants which establish themselves readily among the edging stones and at the sides of the slabs in the pathway itself. Such are the Woodsias, Asplenium and other Alpine ferns, the creeping Sandwort (Arenaria) and the little violet flowered Wall Erinus (E.alpinus).


Herein lies the beauty of the rock garden, for even as we walk there are flowers crowding the pathway, space is never wasted, there is always some tiny plant willing to occupy the smallest crevice.


Rough steps connecting the different levels add much to the picturesque appearance of larger rock gardens. They should be quite informal, and if carefully made will look as though they had been roughly hewn out of the living rock.


A long narrow stone slab should be fitted to the front edge of each step, or if this cannot be managed, two or even three smaller pieces connected by sunken cement joints. The cement will afterwards be concealed by small plants and mosses, which may be naturalised by the scattering of a few seeds in a pinch of soil.


It is not necessary to pave the tread of the steps, but a few pieces of flat stone may be inserted here and there. For the rest, they may be made firm and level with earth and coarse gravel.


In a short time the plants bordering the steps will throw out creeping stolons, draping the sides, dwarf Campanulas will thrive in the joints, and in the corners, safe from the foot of the careless, Rockfoils and Stonecrops will thrust forth their tiny blossoms.




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