This is an easy one: Stop pruning. By pruning your oakleaf hydrangea (Hydrangea quercifolia) in spring, you're removing the flower buds before they get a chance to bloom. Prune oakleaf hydrangea only in summer right after the flowers fade. Although oakleaf hydrangea prefers a partially shaded spot, too much shade keeps it from blooming. Make sure it gets sun for about half a day.