Garden steps of field stone (Fig. 175) in fashion with the retaining walls may be so constructed as to leave pockets for the planting of Alpines. Following a first principle of wall construction, such steps should be as regular as possible, not in absolutely straight lines, but the structure in general should be regular and uniform. This regularity should not be followed in the planting;
Fig. 176. - Stone steps making an interesting approach to the rock garden. Large field stones form the treads with earth risers. Sedum acre (Wall Pepper) is planted between the stones. - See page 229.
Fig. 177. - Small, compact growing shrubs are introduced into a rock garden not only for their floral beauty, but to add stability. - See page 230.
on the contrary, it may be very much varied. An important consideration in the building of such steps is stability. Large, heavy stones should be selected for the base and placed on a firm foundation. As the other stones are placed they should all lie firmly and the soil between be well rammed to prevent too much settling. The planting may usually be done as the work is in progress; the plants will then be better placed, the roots spread more easily. The pockets for plants should be so made as to prevent the crushing of the roots as the work progresses. Plants that show to best advantage on a flat surface should be given the preference, but in not too great a variety. Plants suitable are Rock Cress (Arabis albida), Wall Pepper (Sedum acre. - Fig. 176), Bugle (Ajuga repens), Harebell (Campanula rotundifolia), Soapwort (Saponaria ocymoides) and Speedwell (Veronica rupestris).
Great care should be taken in planting Alpines or many failures will result. Late Spring is the very best season for planting and if it is possible to secure small potted plants they are more easily-handled. Planting and building may often be done at the same time and this is advisable where possible.
The introduction of small, compact growing shrubs will give an appearance of stability to the rockery and deter the eye from taking in too much at a time. Many of the hardy heaths are suitable for this purpose, as are also the Andromedas, Azaleas (Fig. 177), Daphnes, Dwarf Rhododendrons and Cotoneasters.
Coniferous evergreens should be used sparingly in the rock garden. The tall, upright types are not in keeping, and all those with golden or silvery foliage should be omitted. Some of the dwarf Junipers, such as J. tamariscifolia and J. sabina prostrata, are useful, as are the dwarf Spruces such as Picea Remonti, and the dwarf Retinisporas as Retinispora obtusa nana.
The hardy heaths bloom from April until July. The first to bloom is Erica mediterranea. This variety makes its flower buds in the Summer and blooms the following April and May. Other hardy kinds are E. Tetralix, E. cinerea, E. vagans, E. ciliaris and Calluna vulgaris.
Used in the rock garden the heaths should be planted in clumps rather than as individual plants. A rather peaty soil should be provided and the plants placed close together, protecting the roots from wind and undue exposure.