The term “old wood” refers to hydrangea stems that grew during the previous season. These stems form flower buds in late summer or early fall, which remain dormant through winter. Since the buds for the next year’s display are already present on this established growth, the timing of pruning is exceptionally important. This guide details the specific actions and timing required to maintain these shrubs without sacrificing the flowers.
Recognizing Old Wood Hydrangea Varieties
Identifying your hydrangea type is the initial step before pruning. The most common varieties that bloom exclusively on old wood include the Bigleaf Hydrangea (Hydrangea macrophylla), featuring mophead and lacecap forms, and the Oakleaf Hydrangea (Hydrangea quercifolia), known for its deeply lobed foliage and peeling bark. Mountain Hydrangeas (Hydrangea serrata) also fall into this category. These species contrast with “new wood” bloomers, which flower on the current season’s growth and allow for more flexible pruning.
Confirmation of an old wood bloomer often comes from the appearance of the stems. The canes are typically thicker, tougher, and have a woody texture, often turning gray or brown as they age. Knowing these physical characteristics helps confirm that the plant relies on last year’s structure to deliver the next season’s color.
The Critical Window for Pruning
The most appropriate time for pruning old wood hydrangeas is immediately after the current season’s flowers have faded. This period typically occurs in mid to late summer, spanning from July through early August. This narrow window ensures that necessary cuts are made before the plant begins setting new flower buds for the following year.
The strict timing is dictated by the plant’s natural cycle of bud development. Once the summer bloom is complete, the hydrangea rapidly shifts energy to forming the next year’s flower buds along the stems. Pruning after this new bud formation has begun will remove the structures that hold the next season’s color.
Pruning too late in the season, such as in the fall, winter, or early spring, will eliminate a significant portion of the developing flower buds. This mistake is the most common reason for a lack of blooms. Completing all shaping and thinning cuts before mid-August allows remaining stems sufficient time to mature and set buds before cold weather. This specificity makes summer pruning mandatory for consistent flowering.
Techniques for Pruning Old Wood
Pruning old wood hydrangeas is generally a light process focused on maintenance, not severe shaping. The first technique is deadheading, which involves removing the spent flower heads. Make these cuts just above the first set of large, healthy leaves or a visible, strong bud beneath the faded bloom.
For structural maintenance, focus on thinning the shrub to improve air circulation and encourage new, vigorous growth. Selectively remove the oldest, weakest, or most congested canes entirely at the base of the plant. Do not remove more than one-third of the total canes in any single year. This thinning helps manage the shrub’s size and promotes overall plant health. Stems that are clearly dead, damaged, or crossing and rubbing against others should also be removed completely.
Handling Damage and Rejuvenation
Pruning for damage or severe neglect represents an exception to the summer timing rule. Winter-killed wood, which appears brittle and brown, should not be removed until new growth begins in the spring. Waiting until new leaves emerge clearly defines the living tissue, allowing you to cut the dead portion of the cane back to a healthy, green bud or a point just above ground level.
If a hydrangea has become severely overgrown, tangled, or has stopped flowering due to age, a process called rejuvenation pruning can be implemented. This restorative technique involves removing one-third of the oldest, thickest canes each year over three consecutive years. By spacing the cuts over multiple seasons, the shrub is gradually renewed while allowing the remaining two-thirds of the canes to produce flowers. This methodical approach prevents the total loss of blooms that occurs from cutting the entire plant back at once.