A frequently asked question is "should I prune my oakleaf hydrangeas coming out of winter"? My general response is no, because you will be reducing the flower count in June. However, if you missed making last summer's cutbacks (or cleanups), you may remove 20-25% of the dormant branches and only sacrifice a few flowers. Broken, diseased wood, plus bottom suckers may be removed to improve the appearance of the overall plant.
Oakleaf hydrangeas set their flower buds for next spring on both old or current season’s growth on the terminal bud. Do not practice pruning in the fall as it may stimulate new soft growth which dies over a cold winter. Make all cuts 1/4 inch above the last set of leaves or cutback flush to a main branch.
Summer pruning improves the health of oakleaf hydrangeas and stimulates new vegetative growth. On older 4-5 year old hydrangeas, remove larger, thicker canes and prune them at the base of the stem.
What about old neglected oakleaf hydrangeas? Remove one-quarter to one-third of these older branches. In 3-4 years the shrub will be completely rejuvenated.
Dead, dying, diseased stems, and old flower heads can be removed at any time of year.
