Rock Garden Substitutes for Naturals Stone
Some gardeners would advocate eliminating all from the garden layout unless the ideal stone can be obtained, but so many really lovely and artistic little rockeries are made by amateurs all over the country, that this seems an unnecessary restriction. Necessity is the mother of invention, and the really keen amateur rock gardener who cannot afford limestone or sandstone will make a very good attempt by using large flints taken out of the subsoil, old bricks left by the builders, lumps of cement foundation obtainable cheaply from house-breakers, and so on. Concrete, mixed in the proportion of one part cement and two parts sand, and run into containers of various shapes and sizes, makes efficient rockery stones, and if these are built in a careful manner, and set with small creeping plants which will quickly encroach over the rocks, a very natural-lookingis soon created.
How to Begin
The first step in making a rockery is to decide roughly on the contour; that is to say, to decide whether you will have a rockery mound, rising between paths, or at one end of a lawn, or a deep ravine with a path along the bottom and rocky slopes on each side, or whether theis to be built in the form of a steep slope tfith water trickling from the upper level in a series of cascades to a pool at the base, or with a rocky “mountain path” descending down the slope instead of water. Any of these ideas can be carried out quite simply, even in a small space. On a natural slope, the imitation mountain side will be easiest to construct, but on a flat site the style is not very material. Soil has to be excavated at the sides to form the central mould or in the centre to form a ravine.
The rock gardener must not forget that the top spit ofis always most fertile. Where the making of the rock garden necessitates much excavation and alteration in contours, the best plan is to strip off this top fertile soil, and to pile it in a heap at one side while the general outline of the rock garden is being built up. In the case of a very small rock garden the next step would be to trench the soil all over the site, and to fill in at least a 6 in. layer of rough material, such as gravel, or old bricks below the subsoil. This ensures good drainage over the whole of the rock garden. The subsoil is then roughly re-built to the desired form.
If a ravine is constructed, the sides should not be of an even slope, but should be wavy in outline. Where it can be so arranged, the steepest slopes should be on the sides facing the north, while the sunnier south slopes are not so steep. This not only means that the plants will suffer less from lack of moisture on the hot sunny slopes, but it also provides a larger surface area of rockery pockets in full sunshine, and the majority of rock plants are sun lovers.
It is because rock plants love sunshine that a rock garden should always be built in an open sunny part of the garden. The idea of putting a rockery where nothing else would grow, such as under the drip of trees, has fortunately disappeared in most gardens. Hardly any of Nature’s are made under such conditions. There are of course charming rocky dells, in deep crevices in the limestone hills, and other similar situations, but in such places the majority of the plants grown areand other , and not the brightly coloured flower masses which the amateur probably wants in his rock garden.
Setting the Rocks
It is in the placing of the rocks in the garden that the amateur gardener shows his artistic taste. The actual building is done from the bottom upwards. Each stone is selected with care and is so placed that it is both quite firm in the soil, and at the same time slightly tilted inwards into the slope of the ground. The reason for the tilt is that rain, as it falls, will travel naturally into the rockery, where the plant roots are waiting for it, and not be carried away down the outside. Stones so placed will form natural ledges to support the soil, that is to say, there will be “pockets” of soil, in which plants can be set. This method of building gives a natural appearance. Nature’s own are formed where stones have crashed down the mountain side and lodged in this position, and fine soil has been washed down after them and been caught by them in natural pockets.
If limestone is used, the weather-worn lichen covered portion, which is the most artistic in appearance, will naturally be put upwards. Very round and very Hat stones will both be avoided in the main part of the rockery. The round stones can be used in informal pools where water ripples, and flat stones can form part of the rockery paths.
If there is a natural strata to the rocks, that is to say, if they are lined with parallel lines, these should mostly be placed so that they are uniformly horizontal or sloping. This again gives a picturesque appearance to the garden, as if there were a natural outcrop of stone.
Making a Cascade
It is really far more simple than it seems to make a cascade of water in a little garden. It can be done in any garden when a tap can be arranged at the highest spot of the rock garden, and a lily pool or sump arranged to take the surplus water in the lower part of the rock garden. In some cases it may be possible to take the water back to the main drains. Many amateurs have made rock and water gardens in this way, using the water from the house and outbuilding, and the possibility of such a feature should be considered when a new rock garden is built.
There are in Nature two kinds of moraine, both the same except in the matter of age. As a glacier recedes (and all our European glaciers are gradually receding) it leaves in its wake a pell-mell drift of stones, often piled in one place by the meeting of two glacier streams. At first these are partly covered by icy water flowing from the glacier. In time these stones, and also the soil formed by the breaking up of the softer material, are left high and dry, with no icy water, but only the rains of heaven to sustain the plant life among them.
It is naturally impossible in British gardens to reproduce the conditions of the first described moraine, where icy water still trickles through the stones; but the rather older moraine, where most of the water has gone, and the surface stones are dry at all times, can be reproduced. If, at the same time, a subterranean trickle of water (such as the escape of a rockery cascade) can be allowed to pass under the artificial moraine, a fairly cool root run will be secured, and this will give the nearest possible resemblance to the natural moraine that the rock gardener can contrive.
One of the easiest ways to reproduce moraine conditions in an ordinary garden is to use a bank, preferably one facing south, with a gradient of not more than one in ten. A large number of small stones, weathered and water-worn, plenty of grit, and a little soil, are needed for building. (If water naturally oozes from the bank, so much the better.)
Put a layer of coarse sand at the bottom, add the stones and grit, and mix a little fibrous loam with the grit as you work. It is an advantage if this type of garden is above the ordinary level, as moraine plants are very liable to suffer from surface damp.