Trim flowering shrubs like lilac, rose of Sharon and forsythia in late winter or early spring to help promote growth and maintain the overall health and well-being of the bush. By trimming from early in the plant's life, potential problems are prevented and growth is promoted. Before starting, keep in mind the natural form of the shrub. For instance, forsythia has arching branches, so it should be pruned to maintain its cascading form. With a regular maintenance schedule, shrubs can prosper and flourish through a long and healthy life.
Trim flowering shrubs in late winter or early spring, before new foliage and blooms appear and while the bushes are dormant. Pruning during this time allows for easy access to the plant; the foliage and buds do not obscure the overall structure of the shrub.
Cut back the shrub to the first pair of outside buds so the new shoots do not grow or crisscross into the interior of the shrub. Use pruning shears to make a 1/4-inch cut above each set of buds.
Thin back leggy branches by cutting the branch at the point of origin from the main or "parent" stem, to a lateral side branch. This opens up the flowering shrub to ensure more light filters into the plant.
Cut off all broken or criss-crossed branches to keep a natural shape and form. Remove all disease- or insect-infested branches completely and discard away from the garden to prevent infecting other plants.
Sparingly trim back all young shrubs to keep the natural shape; don’t prune the main stem leader. Once the young shrub grows, remove the lowest branches that are clustered around the trunk.