How to Prune Hydrangeas

Pictured: Let's Dance® Blue Jangles® Photo by: Proven Winners.

The first step of pruning hydrangeas is to identify the variety, as this determines how, when, and even if it needs pruning. There are 2 main groups of hydrangeas:

Group 1: Those that bloom on last year's growth, or old wood, and should be pruned in late summer:

• Oakleaf hydrangeas (H. quercifolia)
• Bigleaf hydrangeas (H. macrophylla)
• Mountain hydrangeas (H. serrata)
• Climbing hydrangeas (H. petiolaris)

Group 2: Those that bloom on new growth, or new wood, and should be pruned in late winter to early spring:

• Smooth hydrangeas (H. arborescens)
• Panicle hydrangeas (H. paniculata)

There are also new varieties called "reblooming" or "remontant" that bloom on both old and new wood. These types don't require pruning at all, just maintenance for plant health such as cutting out dead, diseased, damaged or crossing branches.

HOW TO PRUNE HYDRANGEAS

The timing and degree of pruning is determined by which group the plant belongs to:

Pruning Advice for Group 1:

• Buds for next year’s flowers form as days grow shorter and temperatures cooler during late summer and fall.
• Typically, only a trimming is needed to maintain shape, size, and a healthy plant by cutting out dead, diseased, or broken branches. Otherwise, harsh pruning should be avoided.
• Trimming should be done immediately after flowering stops in summer, but no later than August 1. Do not prune in fall, winter, or spring or you could be cutting off new buds.
• Tip-pruning the branches as leaves emerge in spring can encourage multiple, smaller flower heads rather than fewer larger flower heads.

Pruning Advice for Group 2:

• Flower buds form on current year’s growth.
• Prune in early spring, just as leaves are beginning to show.
• Cut branches back by one-half to one-third, cutting just above a node.
• Next, remove any weak or spindly branches.
• For H. arborescens, minimal pruning promotes large vigorous shrubs with numerous, smaller flower heads. Hard pruning 12 to 18 inches from the ground or even all the way to the ground, will produce fewer, but larger, flower heads that may flop without propping.
• For H. paniculata, in order to create a strong framework, prune out surrounding smaller wood, leaving the larger stems.

Flower head size can be related to pruning. With more aggressive pruning, shoots will be more vigorous and flower heads will be larger and fewer. Less aggressive or tip pruning can result in smaller but more numerous flower heads.

The best advice for hydrangeas is to consider their mature size. Locate them in an area they won't outgrow and require heavy pruning to keep them in bounds. Hydrangeas do not require strict reqular pruning; simply keep them healthy by removing dead wood and they will grow and flower well.

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