Pruning can rejuvenate an old bush, change the growing direction, or rid your bush of diseased foliage. Pruning is also the key to creating a better shaped, bushier shrub. When to prune depends on the shrub type. Spring flowering shrubs, such as lilac, weigela, and viburnums bloom on old growth, or last year's growth. Prune these shrubs just after flowering is completed, or you risk cutting off the bloom buds for the next season. Summer flowering shrubs, including hydrangea, rose of Sharon, and potentilla, bloom on new wood or the current season's growth. Prune these in late fall or early spring before new growth begins.
Use your fingers to pinch the top few inches of new tip growth, up to several times through the growing season, to increase the bushiness of smaller, younger shrubs. This method, known as pinching off, is highly effective with evergreen shrubs as well.
Prune using heading cuts to achieve a fuller canopy in larger shrubs while still allowing light and air into the center of the shrub. Heading cuts are made by selecting branches of varying heights to reduce by about 1/3 of their length. Cut 1/4 inch above the bud at a 45-degree angle. The bud is now stimulated to produce new growth, in the direction of the cut.
Use thinning cuts to change the overall shape of a shrub that has become too thick at the base. Thin by cutting up to 1/3 of the old canes or branches back to their origin point. Some branches will be cut back to the main stem, and some to the ground. New growth is directed up and out from the middle rather than spreading or becoming dense in the center.
Keep tools clean by disinfecting them with rubbing alcohol after cutting off branches or foliage that appear to be infected. Diseased or dead material should be disposed of promptly, as infection can grow on dead foliage to spread further the following season.
Water well and keep the soil moist, especially if the pruned shrub appears to be stressed afterward.
Fertilize on schedule, but avoid fertilizing a spring flowering shrub when pruning in the fall. New growth may be stimulated that could interfere with the shrub's dormancy for the winter.
Keep vigilant against pests, as they may find the cut areas of the shrub attractive. Strong sprays of water from a garden hose will dislodge some undesirable insects, such as aphids. Insecticidal soap, available at garden centers, may be a simple solution to a pest problem.