With beautiful clusters of white flower heads in summer and large oak-like leaves that blush burgundy in autumn, the oakleaf hydrangea (Hydrangea quercifolia) is a beloved shrub for woodland gardens. A southeastern American native shrub, confusion arises as to when to prune. Although little pruning maintenance is required annually, an occasional stem reduction in spring can cause lush new growth but causes one season of diminished flowering. You can also reduce stems no more than one-half their length for new stem rejuvenation immediately after the flowers fade in early summer.
Pruning in Early Spring (Before Flowering)
Make crisp, one-emotion cuts with a pruner into the stems of the hydrangea one-quarter inch above a bud on each stem. Reduce each stem to a height of 30 to 40 percent when the plant is dormant in early spring, before buds swell. You are removing stems that are destined to produce flowers later in the spring.
Allow the hydrangea to regrow new stems from the buds below where you made the pruning cuts in early spring. The growth of stems should be profound and lush across the summer, but lack flowers.
Refrain from further pruning stems on the plant, especially in mid to late summer when next year's flower buds are forming on the young stems.
Pruning in Early Summer (After Flowering)
Make cuts into stems one-quarter above a leaf attachment with a sharp pruners. You have two options, cut off just below the fading white flower heads on the stem tips, or reduce the length of the stem no more than one-half the original height. These prunes must be made immediately after flowers fade, no later than summer, such as in mid to late June.
Allow new growth to rise from the buds at the bases of leaves on the pruned stems for the remainder of the growing season.
Hold off on any stem pruning of the oakleaf hydrangea for the rest of the year. Removing stems in fall and winter also removes the dormant buds that will bear flowers the next spring.