Another defect in common ornamental planting, which is well illustrated in the use of poplars, is the desire for plants merely because they grow rapidly. A very rapid-growing tree nearly always produces cheap effects. This is well illustrated in the common planting of willows and poplars about summer places or lake shores. Their effect is almost wholly one of thinness and temporariness. There is little that suggests strength or durability in willows and poplars, and for this reason they should usually be employed as minor or secondary features in ornamental or home grounds. When quick results are desired, nothing is better to plant than these trees; but better trees, as maples, oaks, or elms, should be planted with them, and the poplars and willows should be removed as rapidly as the other species begin to afford protection. When the plantation finally assumes its permanent characters, a few of the remaining poplars and willows, judiciously left, may afford very excellent effects; but no one who has an artist’s feeling would be content to construct the framework of his place of these rapid-growing and soft-wooded trees.
I have said that the legitimate use of poplars in ornamental grounds is in the production of minor or secondary effects. As a rule, they are less adapted to isolated planting as specimen trees than to using in composition,—that is, as parts of general groups of trees, where their characters serve to break the monotony of heavier forms and heavier foliage. The poplars are gay trees, as a rule, especially those, like the aspens, that have a trembling foliage. Their leaves are bright and the tree-tops are thin. The common aspen or “popple,” Populus tremuloides, of our woods, is a meritorious little tree for certain effects. Its dangling catkins (Fig. 33), light, dancing foliage, and silver-gray limbs, are always cheering, and its autumn color is one of the purest golden-yellows of our landscape. It is good to see a tree of it standing out in front of a group of maples or evergreens.
Before one attains to great sensitiveness in the appreciation of gardens, he learns to distinguish plants by their forms. This is particularly true for trees and shrubs. Each species has its own “expression,” which is determined by the size that is natural to it, mode of branching, form of top, twig characters, bark characters, foliage characters, and to some extent its flower and fruit characters. It is a useful practice for one to train his eye by learning the difference in expression of the trees of different varieties of cherries or pears or apples or other fruits, if he has access to a plantation of them. The differences in cherries and pears are very marked (Figs. 34-36). He may also contrast and compare carefully the kinds of any tree or shrub of which there are two or three species in the neighborhood, learning to distinguish them without close examination; as the sugar maple, red maple, soft maple, and Norway maple (if it is planted); the white or American elm, the cork elm, the slippery elm, the planted European elms; the aspen, large-toothed poplar, cottonwood, balm of gilead, Carolina poplar, Lombardy poplar; the main species of oaks; the hickories; and the like.
It will not be long before the observer learns that many of the tree and shrub characters are most marked in winter; and he will begin unconsciously to add the winter to his year.