Evergreens need but little pruning. The pruning of evergreens is done to secure formal shapes, to thicken growth, or to preserve symmetry. Tips of branches should be sheared in the spring just before they start growing. Begin pruning a year after planting and continue each succeeding year. Evergreens dry out more rapidly than deciduous growth and as they make much growth in the early spring, wounds from spring cutting heal rapidly. April is a good month for this work in the northern states. Pinching back of buds at any time in order to thicken the growth is all the pruning that most evergreens require. Shearing for formal shapes must "be done carefully and a portion of the past season's growth allowed to remain on the plants. Many evergreens such as the plume-shaped cypress, Lawson's cypress, and the arborvitae will respond to severe pruning operations. These plants grow vigorously under ideal conditions and during the growing season it is not infrequent that they require pruning two or three times. Rarely are evergreens pruned for the purpose of removing branches which are crowding, and only under very abnormal conditions is it necessary to prune evergreens in order to remove dead or diseased branches.
The pruning of rhododendrons, as a rule, is unsatisfactory, particularly if the wood is old. If the plant is very thrifty, and in a damp, sheltered position, fair success may be had. Not more than one-half of a plant should be pruned in any one year and the other part in the succeeding year. It should be done early in the spring and the bark of the stumps well moistened at least twice daily to assist the development and breaking through of the dormant leaf buds. Cuts should be made just above a whorl of leaves because adventitious buds will appear there more promptly than elsewhere. If the plants are not thrifty it might be advisable to cut half of the stalks to the ground, using care not to decrease, more than is necessary, the beauty of the plants. New shoots will be developed from the ground, and when these reach a satisfactory height, repeat the process with the remaining stalks. The root system will also be benefited by such treatment.
Pruning is seldom resorted to with rhododendrons in order to produce increased size and quantity of flowers. As an added precaution for the successful development of rhododendrons all the seed pods should be removed from the finer and less vigorous growing plants immediately after the flowering period is complete and before any of the plant energy has been expended in the development and ripening of the seed pods, thus diverting this energy into the production of new flower buds instead of into the production of useless seed pods.
Vines are pruned only to remove dead wood and straggling growth. Prune vines after blooming, except vines with ornamental fruit; the latter should be cut back severely in the spring, because they fruit on the new wood.