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Wall Gardening (To the stability)

to the stability of the structure. Each successive layer of stones in the wall should be placed a little further back than those of the previous layer, so that the wall, when seen in profile, will appear to slant slightly backwards. It matters not whether the stones are of a uniform shape or not, it is of greater importance that the same kind of stone be used throughout and to so place them that their strata run in the same direction. The layers should be placed in such a way as to avoid two joints from occurring one directly above the other. Dry walls that are used as retaining walls and are built against a sloping bank have only one side for planting. This is usually the case, but sometimes it may be desirable to construct a dry wall for use as a garden enclosure or as a boundary between the different parts of the garden or place, often making it possible to plant both sides. In such cases it is necessary to make the wall sufficiently thick to prevent the soil from drying out too rapidly during hot dry weather. The exact thickness will vary with the height. Planting and constructing of both sides must be done simultaneously so that the layers of soil will extend solidly throughout the structure, thus avoiding the danger that might otherwise occur of not securing a continuous soil union between the two sides of the wall. Almost any soil that is reasonably fertile is [103] suitable for use provided it is sufficiently light in character. Its natural fertility can be increased by an admixture of leaf mold and very old, thoroughly welldecomposed manure. Soils not sufficiently porous in texture may be improved by the addition of coarse builder's sand.

The most desirable exposure for the rock garden in this climate is a north or northeastern one. A southeastern exposure is too hot for the majority of rock plants unless some shade is supplied. Veronicas, Sedums, Alyssum, Aquilegia, Campanulas and Daphne Cneorum might be used in hot southern exposures.

During warm, dry spells it will be well to water the garden two or three times a week; for this reason the wall should either be constructed near a water supply or a sub-irrigation system should be installed.

In the opinion of the writer, the spring is the best season for planting a rock wall; but this work can also be done in late August or September. Before any planting begins it is necessary to have a definite planting plan worked out: this need not be drawn to scale, any rough sketch showing the distribution of the desired planting will answer the purpose and be a great help while the work is in progress. The arrangement of the plants on a rock wall should receive even more careful thought than those in the flower garden for the [104] reason that any changes made after the building is completed are difficult at best; then, too, some plants are very vigorous growers and extremely hard to eradicate when once they are firmly entrenched in their quarters. Let the grouping of the plants be as natural as possible; do not attempt to crowd a great number of different kinds of plants into a small space, but rather limit the variety of material used sufficiently to permit of a generous grouping of each kind. While the structure of the dry wall should to a certain extent be uniform and regular in outline its planting must be natural and irregular in order to avoid a spotty effect that is ruinous to the artistic beauty which is the chief charm of rock walls. Large groups of each kind of plants, so placed in reference to their neighbors as to make a harmonious whole is much more beautiful than a great variety of different subjects crowded together without any particular thought as to desirable combinations. The habit of growth of the plants to be used must also be taken into consideration; a mistake often made is to place a small upright plant too close to hanging varieties which in time completely crowd out the slender growers. Close grouping of plants is not advisable in the rock wall; give each individual ample space in which to develop to the full extent of its beauty, discarding plants that crowd each other is [105] often not an easy task; weeds must be watched for and pulled out in their infancy before they have a chance to overrun the wall with their vigorous growth. The care of the wall garden is of the simplest and when once it is well established its addition to the garden is a neverending source of pleasure. Many a rock plant may be planted in the crevices and joints of stone steps. Arabis, aubretia, alyssum, iberis, sedum, campanula rotundifolia, and phlox subulata are among the best rock plants suitable for this purpose. As in the building of the wall the plantings around the steps is best done while construction is in progress. The roots of the plants are then better distributed and the ease with which the work may be accomplished is vastly increased. Set the stones firmly in the ground, laying them all upon their flattest surface. If two or three are to be used to form a step the cement necessary to bind them together should be used at their base and ample spaces left above and below, offering opportunities in odd places for the introduction of soil; in this way many a little pocket may be formed in which plants may be grown.