The question of the necessary pruning required by various trees and shrubs is a natural one. Many persons are under the impression that every tree and shrub requires a certain amount of pruning each year. Many are under the further impression that all of this pruning should be done in the winter and spring, while others are under the impression that it should be done during the summer or fall.
The most important fact to be known in connection with the operation of pruning is that one should be thoroughly familiar with the flowering characteristics of the plants to be pruned. Our lawn shrubs especially, which are often subject to the most indiscriminate kinds of pruning, comprise a group of plants with which this chapter is concerned. Pruning is done for various purposes, as outlined and discussed in the chapter on Pruning. The question under discussion in this chapter is whether or not all shrubs shall be pruned at a definite season of the year, and if not, what are the special reasons why this standard method of procedure should not be adopted.
As referred to in the foregoing paragraph, before any pruning of shrubs is attempted it is essential to recognize their flowering habits. The operation of pruning necessarily involves the removal not only of dead wood but of much wood which is alive and growing; wood which produces flowers and, subsequently, fruit. The spring and early summer-blooming trees and shrubs produce flowers from buds which are formed upon the wood during the previous growing season. These embryo flowers contained within the buds have existed in the bud form since the wood of the previous season had begun to ripen, and they are protected by the scales or outer covering of the bud until such time as the temperature has been sufficient to encourage their growth. It is therefore clear that any pruning which is done upon such plants during the late winter or early spring months, prior to the time when these plants have produced their flowers, is an operation whereby a greater or less quantity of flowers is deliberately removed from the plant.
Plate XLVI. Many of our common garden perennials possess the possibilities to produce very interesting colour effects through the colour combination of the flowers. (A) Italian alkanet; (B) hardy marguerite. (See page 231)
An ornamental plant is rarely over-supplied with flowers. It therefore behooves us to preserve, so far as possible, all of the buds which produce flowers. Practically all of the growth of new wood on these plants, which adds to the increasing size of the plant, develops after the plant has completed its flowering period. Buds containing the flowers for the succeeding year are often developed on wood which is formed after the plant has matured its flowers. Therefore, pruning on plants of this kind, such as the mock orange, high-bush cranberry, snowball, and Van Houtte's spirea, should be done immediately after the flowers have matured, to stimulate a correct kind of new growth on which may be developed flower buds for the next season. One of the most common faults in connection with the pruning of trees and shrubs is that of applying the same principles of pruning to all kinds of shrubs regardless of whether they are early spring-flowering or late summer-flowering, and in so doing to deprive the plant of much of its beauty and attractiveness exhibited through its mass of flowers. In such shrubs, of the spring and early summer-flowering types, which produce flowers from buds on the growth of the previous year, pruning, to produce the maximum of new growth for increasing the quantity of flowers during the succeeding year, should never be delayed more than two weeks beyond the time when the plant has matured its flowers.
On the other hand, there is a group of shrubs of which the best examples are the rose of Sharon, butterfly bush, hydrangea, and snow-berry, which are of the late summer and fall-blooming types, and on which the flower-producing buds are formed on the same season's growth. To produce the maximum of flowers on such shrubs it is necessary that they should be pruned during the late winter and early spring months before growth for that season has commenced. In this way much of the old wood is removed, and a greater quantity of new wood, with its accompanying flower buds, is encouraged. If a general rule is to be applied to all trees and shrubs it would be much preferable to give them a so-called summer pruning, which means that the operation of pruning should be delayed until shortly after the shrubs have completed their flowering.
In connection with this discussion it should be borne in mind that there are also some trees and shrubs such as the flowering dogwood, Judas tree, and lilac, which are not so much benefited by annual pruning, and which should be pruned only by the most capable of experts.
There is a group of plants which practically require only the removal of dead wood and superfluous growth. These trees and shrubs are apt to be more or less injured by the operation of pruning. They normally are comparatively slow growing. They have a tendency to grow informally and to maintain the normal shape of the plant as they continue to increase in size. The operation of pruning does not encourage a sufficient new growth and oftentimes so changes the physiological condition of the plant that the flowering ability is impaired to a marked degree during the succeeding one or two years.
From the foregoing discussions it is evident that the operation of pruning, as applied to the questions of just what shrubs to prune in spring and what shrubs to prune in summer, and what shrubs should never or rarely be pruned, is an important one. It is not an operation the decision for doing which should be placed in the hands of any but those who are skilled in the art and those who are thoroughly familiar with the reasons pro and con.