Most deciduous shrubs such as forsythia, deutzia, kerria, lilac, rose-of-sharon, mockorange and weigela usually benefit from annual pruning after you have had them two or more years.
The best time to do most of the pruning is late winter or early spring. But they should not be pruned without a definite reason. Needless and careless pruning can decrease their beauty and value while sensible pruning can enhance their beauty.
The natural form of these flowering shrubs is the most beautiful form and it is best maintained by following a renewal system of pruning, which is more easily and adequately performed during the winter, when it is possible to see the framework and make a better decision what to remove.
The renewal system involves removal of a number of the oldest canes at the ground level. This permits new canes to develop from the base to take their place.
Some kinds - such as forsythia, mockorange and deutzia - often develop canes 6 to 8 feet tall in one season. The bark on these new canes is smooth and bright in color. As they age, the bark becames duller.
With more and more growth at the top, a dense top is created that shuts out light and air from the base. Consequently, new growth that starts from the base is likely to die. This causes the shrub to become leggy.
First remove all dead or damaged canes. Cut them off at the ground level. Then remove about one-fourth of the oldest canes. This way, you get a complete renewal in four years. The following plants can be pruned in this manner: Lilac, deutzia, kerria, blooming in two or three years.
[TEXT OMITTED FROM SOURCE] mockorange, weigela, forysthia, arrowwood viburnum, St. Johnswort, red twig dogwood and Van Houtte spirea.
If too many new canes develop, some should be removed. Usually the strongest should be left. Cutting some of these back one-third will encourage development of side branches.
Privet is often used for a clipped hedge. The plants grow rapidly and tolerate partial shade. Sometimes, after a few years, the privet becomes leggy, with few branches near the ground. Such a hedge can be rejuvenated by cutting it down to about six inches from the ground. Early spring, before new growth starts, is the time to do it. Fertilize the hedge at the same time.
Ligustrum, japonicum, the evergreen privet, will stand heavy pruning to achieve almost any desired shape and size. In case of winter injury, which frequently occurs, or scraggly growth, this plant can be cut back severely in early spring.
Azaleas that are too tall and leggy can be rejuvenated. Select about one-third of the plant, and cut them back to about eight inches from the ground.
Dormant buds below the cuts will start growth and new stems will soon fill the gap. The following spring do another third, and finish the job the next year.
SShearing azaleas immediately after they bloom is not a good idea. It makes the top too dense, shutting off light from the interior.
When the lilac becomes too tall and leggy, cut out a few of the tallest stems each year for a few years. A few of the new stems that appear can be retained to take their place. They should be large enough to start [TEXT OMITTED FROM SOURCE]