You should always prune your shrubs several times through the growing season rather than letting them grow out of hand then pruning excessive amounts at one time. There are specific times to prune as well as specific plant material: Roses should be pruned around valentines day; Trees, specifically shade trees should be pruned during the winter months. Flowering vines and shrubs should be pruned after they have bloomed, the heaviest in spring, late blooming shrubs should be pruned during the winter months as well as vines, ground covers, fruit and nut trees.