A rockery is a part of the place in which plants are grown in pockets between rocks. It is a flower-garden conception rather than a landscape feature, and therefore should be at one side or in the rear of the premises. Primarily, the object of using the rocks is to provide better conditions in which certain plants may grow; sometimes the rocks are employed to hold a springy or sloughing bank and the plants are used to cover the rocks; now and then a person wants a rock or a pile of stones in his yard, as another person would want a piece of statuary or a sheared evergreen. Sometimes the rocks are natural to the place and cannot well be removed; in this case the planning and planting should be such as to make them part of the picture.
The real rock-garden, however, is a place in which to grow plants. The rocks are secondary. The rocks should not appear to be placed for display. If one is making a collection of rocks, he is pursuing geology rather than gardening.
Yet many of the so-called rock-gardens are mere heaps of stones, placed where it seems to be convenient to pile stones rather than where the stones may improve conditions for the growing of plants.
The plants that will naturally grow in rock pockets are those requiring a continuous supply of root moisture and a cool atmosphere. To place a rockery on a sand bank in the burning sun is therefore entirely out of character.
Rock-garden plants are those of cool woods, of bogs, and particularly of high mountains and alpine regions. It is generally understood that a rock-garden is an alpine-garden, although this is not necessarily so.
In this country alpine-gardening is little known, largely because of our hot dry summers and falls. But if one has a rather cool exposure and an unfailing water supply, he may succeed fairly well with many of the alpines, or at least with the semi-alpines.
Most of the alpines are low and often tufted plants, and bloom in a spring temperature. In our long hot seasons, the alpine-garden may be expected to be dormant during much of the summer, unless other rock-loving plants are colonized in it. Alpine plants are of many kinds. They are specially to be found in the genera arenaria, silene, diapensia, primula, saxifraga, arabis, aubrietia, veronica, campanula, gentiana. They comprise a good number of ferns and many little heaths.
A good rock-garden of any kind does not have the stones piled merely on the surface; they are sunken well into the ground and are so placed that there are deep chambers or channels that hold moisture and into which roots may penetrate. The pockets are filled with good fibrous moisture-holding earth, and often a little sphagnum or other moss is added. It must then be arranged so that the pockets never dry out.
Rock-gardens are usually failures, because they violate these very simple elementary principles; but even when the soil conditions and moisture conditions are good, the habits of the rock plants must be learned, and this requires thoughtful experience. Rock-gardens cannot be generally recommended.
(By Ernest Walker)
The beauty of the carpet-bed lies largely in its unity, sharp contrast and harmony of color, elegance--often simplicity--of design, nicety of execution, and the continued distinctness of outline due to scrupulous care. A generous allowance of green-sward on all sides contributes greatly to the general effect,--in fact it is indispensable.
Whatever place is chosen for the bed, it should be in a sunny exposure. This, nor any kind of bed, should not be planted near large trees, as their greedy roots will rob the soil not only of its food, but of moisture. The shade also will be a menace. As the plants stand so thick, the soil should be well enriched, and spaded at least a foot deep. In planting, a space of at least six inches must be left between the outer row of plants and the edge of the grass. The very style of the bed requires that lines be straight, the curves uniform, and that they be kept so by the frequent and careful use of the shears. During dry periods watering will be necessary. The beds, however, should not be watered in the hot sunshine. Foliage plants are most in use, and are the ones which will prove the most satisfactory in the hands of the inexperienced, as they submit to severe clipping and are thus more easily managed.
The following list will be helpful to the beginner. It embraces a number of the plants in common use for carpet-bedding, although not all of them. The usual heights are given in inches. This, of course, in different soils and under different treatment is more or less a variable quantity. The figures in parentheses suggest in inches suitable distances for planting in the row when immediate effects are expected. A verbena in rich soil will in time cover a circle three feet or more in diameter; other plants mentioned spread considerably; but when used in the carpet-bed, they must be planted close. One cannot wait for them to grow. The aim is to cover the ground at once. Although planted thick in the row, it will be desirable to leave more room between the rows in case of spreading plants like the verbena. Most of them, however, need little if any more space between the rows than is indicated by the figures given. In the list those plants that bear free clipping are marked with an asterisk (A):