Hydrangeas make beautiful focal points in the garden, and they require minimal care other than pruning and fertilizing. Although many hydrangeas have interesting foliage and bark, most are grown for their large, showy blossoms. If hydrangeas don’t bloom for a season, it's usually due to one of three reasons: They didn't get enough sun, an early frost or cold spell killed the buds, or they were pruned at the wrong time.
How and when you prune hydrangeas varies according to the six different species of hydrangea commonly grown as garden plants. Thus, you'll need to know (or determine) what species you have in order to prune at the right time of year.
When to Prune Hydrangeas
Like most woody flowering shrubs, when you prune a hydrangea depends on whether it blooms on new wood (growth produced in the current season) or old wood (growth from the previous season). In the case of hydrangeas, this is complicated by the fact that some species of hydrangea bloom on old wood, while others bloom on new wood.
Shrubs that bloom on new growth should be pruned in the late winter or early spring just before the critical new growth has started. This will maximize the amount of new growth and the number of flowers your shrub produces. Shrubs that bloom on old growth, on the other hand, should be pruned immediately after their flowers have faded. This gives the plant plenty of time to develop wood that will be "old" by the time the next season's flower buds emerge.
If you don't immediately know the type of hydrangea you own, it's relatively easy to determine it based on simple observation of its leaves and flowering pattern.
- Bigleaf hydrangeas (Hydrangea macrophylla) have exceptionally large, long serrated dark green leaves (up to 8 inches) and they bloom for an extended period through mid to late summer. The flower color is affected by soil pH; acid soils cause flowers to be blue; alkaline soil causes pink flowers. Along with the large leaves, bigleaf hydrangeas are identified by the large, rounded flowers that bloom in summer. This is one of the species that bloom on old wood; you'll prune this just after the plant is finished flowering.
- Smooth (wild) hydrangeas (H. arborescens) have spring and early summer flowers are that are big and round, either white or shades of pink. The most common garden variety is 'Annabelle', easily identified by its huge snowball-shaped flowers. This plant flowers on new wood, so you'll prune it in late winter or early spring.
- Panicle (peegee) hydrangeas (H. paniculata) have large cone-shaped flower panicles. The flowers are white or green when they first bloom, gradually turning pink. This type is another of the hydrangeas that flower on new wood, requiring late winter or early spring pruning.
- Oakleaf hydrangeas (H. quercifolia), as the name suggests, have leaves that resemble those of oak trees. Their flowers, which bloom early in the season, are cone-shaped and start out cream or green in color, gradually becoming pink. This species flowers on old wood, which means you'll prune immediately after it flowers.
- Mountain hydrangeas (H. serrata) look like a smaller, more compact version of bigleaf hydrangea. Its lacecap-shaped flowers vary in color depending on soil pH. It blooms on old wood but its small size (2 to 4 feet) means that pruning is not needed very often. If you do prune, it will be done immediately after flowering.
- Climbing hydrangeas (H. anomala subsp. petiolaris) are very vigorous climbing vines (as much as 40 feet) with white flowers that appear in spring to early summer. The flowers form flattened clusters up to 8 inches wide. This is another of the varieties that flowers on old wood; when pruning is needed, it will be done after the flowers have faded.
|When to Prune Different Types of Hydrangeas|
|Category||Blooms on old or new wood||When to prune|
|Bigleaf hydrangea||Old||Immediately after flowers fade|
|Smooth (wild) hydrangea||New||Late winter or early spring before new growth starts|
|Panicle (peegee) hydrangea||New||Light pruning in late winter or early spring|
|Oakleaf hydrangea||Old||Summer after the flowers fade|
|Mountain hydrangea||Old||Immediately after flowering|
|Climbing hydrangea||Old||Winter or early spring, only when necessary to control size|
Before Getting Started
In general, flowering woody shrubs that bloom on new wood tolerate, or even thrive on, fairly aggressive pruning, while those that bloom on old wood require more careful restrained pruning. This is especially true of hydrangeas. The two species that bloom on new wood—panicle (peegee) hydrangeas and smooth (wild) hydrangeas—do well with an aggressive annual pruning that removes as much as one-third to one-half of the total mass of the shrub. The four species that flower on old wood—bigleaf, oakleaf, mountain, and climbing hydrangeas—may not need pruning at all, except when you are pruning to keep their size or shape in check.
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Equipment / Tools
- Bypass pruners
- Lawn waste bag(s)
How to Prune Bigleaf Hydrangea (H. macrophylla)
Bigleaf hydrangeas are one of the species that bloom on old wood, meaning they set their flower buds from late summer to early fall. Thus, if you mistakenly prune in the spring or even late fall, it will remove the flower buds and any chance of getting blooms for a year. Bigleaf hydrangeas actually do fairly well without any pruning at all, but if necessary to control its shape or size, do the pruning carefully just after the flowers have faded, never removing more than one-third of their total growth.
Deadhead Spent Flowers
Spent flowers can be trimmed away as they fade to keep the plant looking tidy. Simply clip away the blooms using bypass pruners.
Prune Away Dead and Weak Stems
When most of the flowers have faded, it's time for pruning. Begin by pruning away stems that are clearly dead or weak. But don’t prune all the old wood because this is what will keep flowering as the new growth matures.
Prune for Size
If your hydrangea has outgrown its space and you need to prune it, you can prune away select branches to curtail its size. Prune away select branches all the way to ground level or to a main stem, but make sure to retain some healthy branches to avoid losing all the flowers. A bigleaf hydrangea can be pruned back by one-third of its total mass, but harsher pruning will weaken the shrub and cause it to languish for a season or two.
How to Prune Smooth Hydrangea (H. arborescens)
Smooth hydrangea, including the popular cultivars H. arborescens 'Grandiflora,' 'Annabelle', and 'Incrediball', doesn't usually have any problems blooming, though its white flowers aren't as showy as we normally expect from hydrangeas. It's a round shrub with leaves that are somewhat rounded with a pointed end, paler on the underside than on the top. Blooming on new wood, smooth hydrangea does well with fairly aggressive pruning.
Remove Dead or Injured Branches
This shrub blooms on new wood, so pruning should be done in early spring to ensure plenty of growth for flowers. Begin by removing any branches that have been injured or killed over the winter. These branches should be removed back to the main stem or even to ground level.
Trim for Shape
Additional branches can be lightly trimmed to shape the plant and retain its rounded shape. This kind of light pruning produces a large shrub with many small flower heads. "Light trimming" in this case means removing as much as one-third of each stem's length.
Prune Hard for Large Flowers
Hard pruning of a smooth hydrangea ( 12 to 18 inches from the ground) often creates a shrub that produces fewer, but much larger flower heads. These flowers may be so large that they require propping.
How to Prune Panicle (Peegee) Hydrangea (H. Paniculata)
Also known as peegee hydrangea, panicle hydrangeas produce football or cone-shaped flower clusters in mid-to-late summer. The flowers start out white, cream, or green and slowly turn pink, drying and remaining on the plant long after the leaves have fallen. Panicle hydrangea blooms on new wood; it accepts—and even prefers—fairly heavy pruning.
Deadhead Spent Flowers
During the growing season, you can deadhead the flowers (remove spent flowers) as they fade. This often helps prolong the bloom season as the plant puts more energy into continued blooming.
Prune Lightly to Maintain Shape
As soon as the flowers become unattractive, clean up the overall shape of the plant with selected pruning of branches that spoil the shrub's aesthetics. Panicle hydrangea makes for an attractive shrub even after flowering is complete.
Do Hard Pruning in Late Winter or Early Spring
Flower buds occur on new spring growth with this shrub. Some hard pruning of individual stems in late winter or early spring not only will keep the plant from becoming overgrown but also will encourage healthy growth and flowers. Panicle hydrangeas can be pruned by 1/3 of their total mass without damage to the plant. This is best done by pruning out smaller wood all the way to ground level, leaving only the larger stems—which can also be partly trimmed back if needed to maintain size.
How to Prune Mountain Hydrangeas
Mountain hydrangeas are small flowering shrubs with narrow, pointed leaves and flattened flower heads. This plant is sometimes confused with Hydrangea macrophylla because of their similar flowers. However, this type doesn't have the big leaves of Hydrangea macrophylla. Pruning should be done cautiously—or not at all, if not required to control the shrub's shape. Blooming occurs on old wood, and the plant's pruning needs are minimal.
Remove Dead or Dying Stems in Early Spring
Any dead or winter-damaged stems can be removed all the way to ground level with pruners in early spring, before new growth has started
Prune for Shape
If major pruning is necessary, wait until the shrub has finished flowering to trim back stems to a pair of healthy buds, using bypass pruners. This is not a shrub that always requires annual pruning.
How to Prune Climbing Hydrangeas
The stunning climbing hydrangea is the type you see slowly making its way up a tree or other support. Rather than a classic shrub, it is a woody vine and it normally requires little to no pruning except to control its size. This plant flowers on old wood grown during the previous season, so any major pruning you do should be done immediately after the plant flowers.
Prune to Control Size
Once climbing hydrangeas become established, they can grow quite vigorously and might need occasional hard pruning to set boundaries for the coming season. Do this pruning immediately after the plant flowers. Most flowers occur at the top of these plants, so side trimming will have less impact on the plant's appearance.
Special Pruning to Rejuvenate a Neglected Plant
Neglected, overgrown vines can be cut back to ground level in early spring to rejuvenate the plant. However, you can expect this to reduce flowering fairly dramatically for one or two seasons.
How to Prune Oakleaf Hydrangeas (H. quercifolia)
Oakleaf hydrangea is easily recognized by its oak leaf-shaped foliage. Because its major attraction is the foliage, any loss of blooms is less disappointing than in most other hydrangea varieties. Oakleaf hydrangea flowers on old wood and major pruning should occur immediately after it has finished flowering. Be somewhat cautious when pruning an oakleaf hydrangea—prune is done to control size or shape, not to stimulate new growth.
Prune Out Winter Dieback
Inspect your shrub in the early spring before growth has begun. If your shrub has experienced winter dieback, prune the stems back to below the point of injury. Further pruning should wait until the plant has finished flowering.
Prune for Shape
Oakleaf hydrangea blooms on old growth, so any hard pruning that's required should be done immediately after it has finished flowering. Use sharp bypass pruners to remove branches that interfere with the desired shape of the shrub. This variety is not fond of heavy pruning, so never remove more than one-third of the plant's total mass, and don't feel obliged to prune at all unless it is essential to maintain the plant's size or shape. Cut selected stems back to just above the point where they meet the main stems.
Guide to Pruning Hydrangeas. University of Maryland Extension