THE FLOWER GARDEN 149 



two inches to the foot. The thickness of retaining walls will de- 

 pend 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 struc- 

 ture 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 plant- 

 ing 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. 



GARDEN STEPS 



Garden steps (Fig. 123) built of stone or brick require a greater 

 breadth of treatment than is necessary for these features in connec- 

 tion 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 appear- 

 ance. This is more pleasing than the harsh lines of the cheek 

 blocks. 



PIERS 



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 con- 

 ditions it is more pleasing to have a ramp (Fig. 124) from the top of 



