It is one thing to study in advance the theory of placing the garden water features and rocks but further experience comes with the actual construction of a rock garden. A willing student can soon grasp the essential principles - mechanical, cultural, and aesthetic - to be followed in making the home for mountain plants. Another mental labor of more diverse nature is the study of the identity and habits of rock plants, for the greater quantity of these herbs makes this task far longer than for the usual garden plants.

But the operation of setting the plants actually into the pockets, of planning and producing the combinations, is yet another matter. You will undoubtedly have more failures than successes in planting rock herbs, both from poor cultural methods and unpleasant groupings, but there is no harm in that. After several failures in a soil pocket, there may come a pleasing planting which will endure and be a joy for years, for one success balances several failures.

In staging the plants on plan for this kind of garden, the considerations are quite different from those for a formal garden or hardy border. The things to be kept in mind may be stated first as general principles and then their application to a particular plan may be shown, with the proviso that details can be completed only on the ground at the time of actual planting. Scale is a measure you must apply in every placing, in relation of plant to size of whole area, to the nearer rocks, and the nearest plants, as to height, character of foliage, and mass of bloom.

Usually the plants of more than ordinary growth and of greatest quantity would be put into the larger pockets near the more bulky rocks, with tiny plants and those of lesser quantity taking the smaller areas. There is always the danger that too much of the rock surface will be covered with vigorous foliage growth. On the other hand, near many bold pieces of rock only very dwarf and slow-growing herbs should be placed.

This is done to bring out the grandeur of the ledge, to keep a variation in heights, and emphasize the irregularity of the scene. Along with the danger of covering the rocks there is also that of smothering all the details of the tiny landscape with overvigorous vegetation. There is also a chance that the plants will smother one another. Much of the care of rock plants consists in throwing out weedy and crowding sorts and protecting the weaker ones.

The robust creepers, as Cerastium, must be well penned in by the walls of the pocket and given plenty of room to hang down over the ledge face. Often it is best to keep the plants of the four groups - erect, tufted, creeping, and drooping - by themselves, yet for variety making this separation not too obvious, allowing some erect plants to grow among the drooping ones and bulbs among the creeping kinds. The tufted sorts prefer isolation, and these are usually on the highest spots.