In late winter before bloom, take out the oldest and weakest canes at or near the ground to reduce height, thin and improve flower quality. Some shrubs may need some shoots cut back if outside influences, such as shade, cause the plant to become out of balance. For most summer-flowering shoots, cut back all shoots in early spring to near the soil line. Pruning is an ancient practice that dates back thousands of years. Perhaps the most ancient reference to pruning pertains to grapes, on which severe pruning was and still is practiced to increase fruit production.
Most books describe pruning as an art.
Few, even in recent times, approach pruning as a science. As a result, references place emphasis on the shape and form and less on how a plant responds. Concentrating on shape and form with little or no emphasis on the plant's response too often leads to butchering. There is a big difference between pruning and shearing. Good pruning techniques always take the response of the plant into consideration by making cuts that improve the plant's health.