Panicle hydrangea in tree form

Panicle hydrangeas pruned to maintain a tree-like shape. Photo: M. Talabac,  UME

Updated: February 7, 2024

Why prune hydrangeas?

Hydrangeas do not require extensive or regular pruning, and most pruning is done for aesthetic reasons to:

  • Remove dead growth. Hydrangea varieties vary in their cold hardiness. Winter and spring weather conditions may cause stem damage, such as when mild temperatures are followed by drastic or rapid chilling, or when spring frosts occur after plants begin growth. Freezes may kill only flower buds or entire stems.
  • Manage mature size. There are hundreds of hydrangea varieties with a range of mature sizes. Removing entire stems to force regrowth or shortening tall stems can change the shrub’s size for that season. Tall varieties of panicle hydrangeas are sometimes maintained as a “standard,” which uses pruning to give a shrub the appearance of a small tree.
  • Rejuvenate old plants. Even healthy plants can experience occasional dieback of older stems. Pruning stimulates regrowth, which can freshen a plant’s appearance, and may also stimulate better flowering if the shrub is receiving enough light. In some cases, pruning might increase the size of flower clusters, even if the number of flower clusters is reduced overall.
  • Reduce disease severity. Several leaf spot diseases can infect hydrangeas and cause unsightly symptoms by late summer. The risk of leaf infection is higher when plants are crowded or growth is very dense, such as growing close to neighboring plants or to a wall or solid fence. Reduced air circulation can slow the drying of leaves after rain, dew, or irrigation, creating vulnerability to infection.
  • Remove spent flowers. Aging and faded hydrangea flowers can develop appealing colors and provide winter interest. Some gardeners prefer to remove them before they turn fully brown and dry. Trimming off faded flowers, called “dead-heading,” is not necessary for plant health, though it might encourage faster reblooming for hydrangea varieties capable of repeat flowering.
Dormant smooth hydrangea with spent flower heads
Smooth hydrangea shrubs in a trial garden, illustrating the impact of pruning on flower cluster size. The rightmost shrub has fewer but larger clusters and was cut back and thinned in late winter. The shrubs to its left were not pruned. Photo: M. Talabac, UME

When to prune hydrangeas

Pruning timing depends on the type of Hydrangea you have. Hydrangea species fall into one of three categories based on how they develop their flower buds. Many hydrangeas cannot replace flower buds that were accidentally removed. If a loss of flowers is not a concern, then the timing of pruning is less critical, though still should be avoided close to winter dormancy.

The age of branch growth (wood) that produces the flower buds is the important trait:

  • Old wood is branch growth at least one year old. All of the branches present before hydrangeas break dormancy in spring is old wood. Hydrangeas blooming on old wood develop flower buds during summer and autumn the year prior to when those flowers open. The flower buds lie dormant on the stems during winter, and open the following spring or summer.

    Prune just after the flowers fade. Bigleaf and mountain hydrangeas can be trimmed to about 12 inches off the ground. Oakleaf hydrangea can be pruned to the same height or left taller, especially for large-maturing varieties.

  • New wood is branch growth produced in the current growing season. Hydrangeas blooming on new wood develop flower buds just prior to opening them, either in spring or summer. Overwintering stems do not have any dormant flower buds on them because they have not yet formed.

    Prune in late winter or early spring. Smooth hydrangea can be trimmed to about 12 inches off the ground. Panicle hydrangea can be pruned to the same height or left taller, especially for large-maturing varieties.

  • Remontant is the term used for shrubs capable of reblooming by producing flower buds on both old and new wood. The old wood buds open first, since they were already fully formed at the start of the season, followed by new wood flowers that keep forming well into the summer. Hydrangea varieties bred with this trait benefit gardeners whose shrubs frequently lose flower buds to cold damage, deer browsing, or mis-timed pruning.

    Prune either in early spring or after the first flush of flowers has faded. Early-season pruning will delay the start of flowering, and mid-season pruning might interrupt or shorten the overall reblooming window, so the timing is a personal preference. Pruning height can vary but should remove as little wood as possible to avoid delaying new blooms.

Hydrangea flowering groups and pruning

Old Wood: prune just after flowering New Wood: prune in late winter
Oakleaf Hydrangea
(Hydrangea quercifolia)
Smooth Hydrangea
(Hydrangea arborescens)
Bigleaf Hydrangea
(Hydrangea macrophylla)
Panicle Hydrangea
(Hydrangea paniculata)
Mountain Hydrangea
(Hydrangea serrata)
Bigleaf Hydrangea*
(Hydrangea macrophylla)
climbing hydrangeas**
(Hydrangea anomala petiolaris)
(Schizophragma hydrangeoides)
Mountain Hydrangea*
(Hydrangea serrata)

* remontant varieties only
** climbing hydrangeas are not routinely pruned, but fall into this category

Identifying hydrangea species by bloom type

If you don't know what kind of hydrangea you are growing, compare the flowers to examples below. The only commonly-grown species that can produce blue or purple flowers are bigleaf hydrangea (Hydrangea macrophylla) and mountain hydrangea (Hydrangea serrata).

Bigleaf hydrangea (Hydrangea macrophylla) can have rounded, petal-dense “mophead” blooms (shown here) or flattened, petal-ringed “lacecap” blooms. Mountain hydrangea (Hydrangea serrata) looks nearly identical and has lacecap-style flowers.

Photo: M. Talabac, UME

Oakleaf hydrangea (Hydrangea quercifolia) has characteristic oak-shaped leaves.

Photo: M. Talabac, UME

Smooth hydrangea (Hydrangea arborescens) can have mophead or lacecap flowers. Popular mophead variety ‘Annabelle’ is shown here, though varieties closer to the wild type will have lacecap style flowers with very few petals.

Photo: M. Talabac, UME

Climbing hydrangea (Hydrangea anomala petiolaris) clings to a wooden, bark, or stone support, or sprawls along the ground. Flowers have relatively few petals in a lacecap style.

Photo: M. Talabac, UME

Japanese Hydrangea-vine (Schizophragma hydrangeoides) clings to a wooden, bark, or stone support, or sprawls along the ground. Flowers have few petals in a lacecap style, but often more petals than those of climbing hydrangea.

Photo: J.C. Raulston Arboretum

Panicle hydrangea (Hydrangea paniculata) is the final species to flower and includes an old variety commonly called “peegee” or P.G. hydrangea, which some gardeners use as a common name to refer to the entire panicle group.

Photo: M. Talabac, UME

How to prune hydrangeas

Visit Pruning Shrubs and Hedges for information on these different techniques.

  • Thinning dense plants can improve air circulation through the foliage, which lowers the risk of a disease outbreak like leaf spot. Since this approach removes entire stems, the timing of flowering is less important. Hydrangeas benefiting most from this technique would be the bigleaf and mountain types.
  • Heading back stems to reduce their length will restrain the size of an overgrown plant. When shrubs break dormancy in spring, you will be able to see if any stems have dead tips from winter damage. After their removal, you can then determine how far back to trim the remaining growth. Any hydrangea species can be pruned with this technique.
  • Renewal pruning can refresh a hydrangea that has become too sparse from weather damage or which developed an irregular shape over time. Regrowth should produce a more even growth habit if the plant is not too heavily shaded or crowded on one side. Since this process removes most of the old wood, the plant might not flower well (if at all) for a year or longer while it recovers. Any hydrangea species can be pruned with this technique. Tree-form panicle hydrangeas can be renewal-pruned only if you want to convert them back into a shrubby shape with lower branches; otherwise, their trunks should not be cut down.
  • Dead-heading removes only spent flowers at the branch tips (no further down the branch) and can be performed any time after flowers fade for any hydrangea type. It is not necessary to remove spent flowers to maintain plant health.

Examples of hydrangea pruning and stages of growth

Panicle hydrangea in late winter before pruning.

Photo: M. Talabac, UME

Panicle hydrangea in late winter after pruning, where heading-back cuts reduced stem height. Dense growth and crossing branches can also be corrected with pruning at the same time.

Photo: M. Talabac, UME

Panicle hydrangea in late winter after pruning, with heading-back cuts made just above a bud.

Photo: M. Talabac, UME

Bigleaf hydrangea buds in late winter. The pointed buds on the branch tips as well as the rounded buds below them hold flowers that will open later that season.

Photo: M. Talabac, UME

Lacecap style bigleaf hydrangea with fading flowers. Depending on variety, fading blooms can turn paler and green or blush ruby before drying to brown. Although they do not need removal, if you prefer to dead-head, spent flowers can be clipped off once they lose color.

Photo: M. Talabac, UME

Alternatives to pruning

Rather than regularly pruning an overgrown hydrangea too large for its space, a simpler solution is to either transplant it to another location or replace it with a variety that naturally stays more compact. Breeding efforts in recent years have resulted in a plethora of hydrangea varieties in every major species group, so there are multiple options for customizing the desired mature size of the plant with little or no pruning adjustments.

Dwarf panicle hydrangea shrubs
A very dwarf variety of panicle hydrangea that will not need pruning to maintain size. Photo: M. Talabac, UME
Compact panicle hydrangea shrub
A mid-size, compact variety of panicle hydrangea can more easily fit into a perennial planting or alongside other shrubs without drastic pruning. Photo: M. Talabac, UME

Author: Miri Talabac, Certified Professional Horticulturist & Coordinator, HGIC. 2024

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