Shrubs are divided into three classes according to their height: a, low; b, medium, and c, high. Height is a primary consideration in all planting schemes, as it determines the scale of the entire planting problem.
Figure 31. PARK-LIKE PLANTING AT WARWICK, ENGLAND.
The scale which is to prevail in the planting scheme should in turn be fixed by the requirements of the problem in hand. If a screen were to be planted to hide a garage from the eyes of passers-by, a hedge of California privet would be of little value, as it would not perform the purpose for which it was placed there. It would be necessary to use higher shrubs or even Lombardy poplars, placed close together, if it were really necessary to conceal the building.
The scale of the planting may be determined on one hand by the economic aspects of the problem, and on the other by the esthetic. The height is decided upon first because of utilitarian features, and then for harmonization with existing conditions; also to furnish the amount of emphasis or accent required. High shrubs are called background; medium, filler; and low shrubs, facing. In large scale planting the trees may be used as background shrubs. In small scale planting herbaceous plants are often used as facers.
Figure 32. TREE FORMS.
Plant forms may be roughly divided into rectangular, curvilinear, and triangular divisions (Fig. 32), according to the natural shapes of the trees and shrubs. While the groups may embrace numbers of widely different species, some of the commonest varieties are named in the diagram in order to make it easily understood. A more complex scheme of classification may seem necessary to some, but the one that is shown has proved very satisfactory for general use.
The rectangular and curvilinear classes have four subdivisions; the triangular has two. The extremes in each class are used as accent, for the less exaggerated forms are of greatest usefulness, being employed to do the heavy work in most planting plans. These are the filler plants. The Sambucus canadensis aurea groups may also be divided according to the deciduous and the evergreen members; these are further subdivided into regular and irregular classes.
Figure 33. ROSE OF SHARON Hibiscus.
Figure 35. SNOW MERRY Symphoricarpus racemosus.
Figure 34. THE GOLDEN ELDER-CUT LEAF VARIETY.
Shrubs are often selected for their quality, by which is meant the degree of refinement of their appearance. According to their quality they are divided into three classes: the high class, or named varieties; the medium; and the coarse. An example of a high-class shrub would be the rhododendron. Bush-honeysuckle or mock-orange is a medium class, and the Hydrangea paniculata grandiflora is an example of the coarse species.
The quality of a shrub will often suggest its use. A marble building, such as a museum, a memorial, or a library demands the use of first-quality shrubs. They are decidedly fitting for use amid monumental surroundings. The second-quality shrubs can be used to advantage in most planting schemes, while the coarser varieties will not appear out of place in the meanest surroundings. Where coarse varieties predominate, shrubs of medium quality may be used for accent; and where medium-class shrubs predominate, the high-class shrubs may be used as accent.
For any planting scheme which has high-class varieties it is not best to use other varieties of shrubs. The designer will ordinarily use shrubs of the same class, depending for accent upon difference in shape and color.
Characteristics are the distinguishing features of a plant, that part of its form or development which recommends it particularly to the landscape-designer. Its major interest may be in leaf, blossom, or twig. The leaf may demand attention on account of its scale, for it may be large, as in the catalpa; medium, as in the lilac; or small, as in the spiraea. Or it may attract because of its shape or its regularity, as with the maples and the gingko or the rose of Sharon; or on account of irregular development, as in the mulberry-tree. Then, too, the distinguishing characteristic may be its value, or the amount of light or dark in the green.
Value is divided into three parts: as light, medium, and dark, and these values appear in both deciduous and evergreen plants. The leaves may appear in clusters, rows, or whorls, and demand attention on account of their arrangement; or the entire outline of the leaf masses and their positions on the tree may seem to be of greatest importance. The direction of the leaf, which will be horizontal, vertical, or oblique, will also affect the problem.
Leaves may be grouped in masses, as in the horse-chestnut, or may be scattered, as in the American elm. This will affect the texture of the entire tree or shrub; but the texture of the leaf itself is likewise of importance, as it affects the appearance of the entire leaf mass both near at hand and at a distance. It may be thick or thin, rough or smooth. Leaf texture may easily be understood by comparing the leaf of the California rubber-tree, thick, smooth, and regular, with the small, thin, and serrated leaves of the white birch. The leaves may be many or few in number, and this too will affect the appearance.
The first characteristic of the blossom is size, which means its general appearance as a single flower or a cluster, and may be large, as in the magnolia; medium, as in the Philadelphus; or small as in the spiraea. Blossom color will be discussed under the head of color, and it is of the utmost importance.