What trees and shrubs are pruned in summer?
In general, prune all shrubs and ornamental trees to keep them shapely. Broken branches and cross-branching always need to be removed. Specifically, prune climbing and rambling roses after their first flush in spring and continue to deadhead all other roses throughout the summer growing season to increase flowering. Trees that produce sap in spring such as beech, birch, maple and sycamore are best pruned in summer. Early spring-flowering shrubs such as forsythia, spirea, rhododendron, etc. should be pruned in early summer, after flowering. Evergreens like yews, boxwood and arborvitae need touch-up pruning in early summer after their growth has slowed.
Courtesy of NYBG Plant Information Service