An alternative garden which can be built with similar materials, but where theis dry and water cannot be introduced artificially, is the scree garden. Where a steep mountain is crumbling, showers of small and large stones rush down to lower levels, and form fan-like heaps against the rock sides. It is hard to imagine a more uncongenial spot for plants than this, but such is the adaptability of vegetation that some plants have developed a fondness for this situation, and thrive best when showers of small stones are frequently washed down on to them from higher levels. Campanula allionii, Peirocallis pyrenaica, and certain of the Kabschia Saxifrages are frequently found in heaps of stones piled against tall cliffs.
A scree garden is built on much the same lines as the moraine, but leaf-mould is used with the bottom layer of sand. Deep-rooting subjects need this for moisture and food.
As already mentioned, a rockery sometimes takes the form of a wall garden. This may be either a retaining wall between two levels on a sloping site, or it may be a division wall, built on the same principle as a retaining wall, but with wall stones on both sides and soil filled into the hollow between the rocks. It is desirable to make a slope of about I| ins., in each foot from front to back, so that the face of the wall is not quite vertical. Special rock stone is sold for building walls, usually in small pieces a few inches thick. Any kind of stone, however, can be used if necessary, the secret being to pack between the stones sufficient rich but sandy soil to sustain the plant roots. Stones must be set very firmly and here and there larger or longer stones must penetrate from the front well back into the bank or soil, or in the case of a double-faced wall, a long stone must here and there lie across the whole width of the wall, in order to give it security.
Plant Wall Gardens as you Build
It is much better and much easier to set the plants in a wall garden as building is being done. Some of the plants succeed better in the vertical crevices than in the others, and also planting is often extremely difficult when the wall is finished.
Should it be impossible to plant during building, the best thing to do later is to mix suitable seeds with a little soil and sufficient water to make it moist, and to press this well into the crevices between the stones. The seeds soon germinate, and establish themselves more quickly than do small plants set into the wall crevices.