How much more effective is a treatment of retaining walls (Fig. 121) than the slope, so generally adopted for each succeeding level! Such slopes are difficult to mow and, in a dry Summer, the turf burns out badly.
The use of stone as retaining walls between garden levels is not so generally adopted as it should be. The dry stone wall is especially worthy of greater use. The foundations of garden walls should always extend at least two feet six inches below grade and batter two inches to the foot. The thickness of retaining walls will depend on the height it is necessary to make them. As a general rule, a thickness at the base of one-half the height will be found satisfactory. A great deal depends, however, on the physical structure of the soil: a sandy, slippery soil will require a stronger wall than a hard, clayey soil, the latter being more self-retaining. Given a retaining wall with a northwest exposure, a scheme of wall planting is possible; pockets may be left in the wall and filled with soil for plants. Alyssum saxatile, Heuchera sanguineum, Sedums, Arabis albida, Aquilegias, Gypsophila, Valeriana, Santolina, and many other plants, are suitable for such a purpose.
Fig. 122. - The Hemlock forms an ideal hedge for the garden enclosure. The dark green color makes a pleasing background for the flowers. - See page 146.
Fig. 123. - Plan for stone garden steps and cheek blocks. When there are a small number of risers it is possible to make the cheek blocks square. - See page 149.
Garden steps (Fig. 123) built of stone or brick require a greater breadth of treatment than is necessary for these features in connection with buildings. The risers should be close to six inches, and the tread at least fourteen inches in width.
Steps either approaching the garden, or within the enclosure, may be built with cheek blocks at the ends or with the ends built into the slope and planted with Ivy or Euonymus to cover the raw appearance. This is more pleasing than the harsh lines of the cheek blocks.
All retaining boundary walls should terminate in piers and the corners and entrances (Fig. 118) of walls and hedges should be defined by similar features.
When the piers are built in a garden where a hedge is to be the enclosure, the piers should be from twenty-four to thirty inches wide; the hedge should be kept the same width and not allowed to become wider than the piers.
Piers at corners or entrances should be built the same height as the wall and the coping (Fig. 118) returned around the pier as a mark of accentuation. An additional stone placed on top of the coping, and set back six or seven inches from the edge, is very effective.
Where the entrance is to be featured by a gate or arch it is necessary to have the piers higher than the wall. Under such conditions it is more pleasing to have a ramp (Fig. 124) from the top of the wall to a point near the top of the pier. This is more pleasing than to have the pier standing high above the wall.
The same treatment should be applied at the intersection of two walls when, for reasons of grade, it is necessary to keep one below the other.
If the garden is on several levels and it is necessary to keep the cross walls flush with the grade a ramp (Fig. 125) should be used to tie the side and cross walls together gracefully.