RHS Pruning Group 4: Summer-Flowering Shrubs
RHS Pruning Group 4 covers deciduous summer-flowering shrubs that generally need only light, selective pruning in spring. The most familiar examples are mophead, lacecap and several other hydrangeas that flower predominantly on established stems.
The objective is not to cut the whole plant hard. Pruning should remove dead flower heads, damaged growth and a limited number of old or congested stems while retaining the healthy framework that will carry the coming season’s flowers.
Pruning these shrubs too severely can remove developing flower buds and leave the plant with healthy foliage but few flowers.
What Is RHS Pruning Group 4?
The Royal Horticultural Society uses pruning groups to organise plants according to how and when they should be pruned.
Group 4 is mainly associated with deciduous shrubs that flower in summer and require relatively light spring pruning. Many form their flower buds on growth produced during an earlier season.
This means they should not automatically be treated in the same way as shrubs that flower on entirely new growth.
The principal aims of Group 4 pruning are to:
Remove dead flower heads
Remove dead, damaged or diseased stems
Improve the shape of the plant
Reduce congestion
Encourage gradual renewal
Retain sufficient established wood for flowering
Avoid unnecessary hard pruning
The exact treatment depends on the species, cultivar, climate and condition of the individual plant.
Which Plants Belong to Pruning Group 4?
Group 4 primarily includes several deciduous hydrangeas, such as:
Mophead hydrangeas
Lacecap hydrangeas
Hydrangea macrophylla
Hydrangea serrata
Hydrangea aspera
Hydrangea involucrata
Hydrangea quercifolia
This is not a complete list, and pruning classifications can differ between species within the same genus.
Check the full botanical name of the plant before pruning. The word “hydrangea” alone does not tell you which pruning method to use.
Not Every Hydrangea Is Pruned as Group 4
One of the most common pruning mistakes is treating every hydrangea in the same way.
Mophead and lacecap hydrangeas generally require light Group 4 pruning because their flowers are associated with established stems.
By contrast, Hydrangea paniculata and Hydrangea arborescens flower on new growth produced during the current season. These are normally pruned more firmly in spring and are generally associated with RHS Pruning Group 6.
Climbing hydrangeas also have different pruning requirements and should not automatically receive the Group 4 treatment.
Always identify the type before making significant cuts.
When Should Group 4 Shrubs Be Pruned?
Group 4 shrubs are generally pruned in spring, as growth begins and the strongest healthy buds become easier to identify.
In many parts of North West England, this is often during March or April, but the weather and location of the garden should guide the final timing.
Gardens in exposed, elevated or frost-prone areas may be several weeks behind sheltered urban gardens.
Avoid relying entirely on a calendar date. Look for:
Swelling buds
Emerging leaves
Clear signs of healthy growth
Reduced risk of prolonged severe frost
A visible distinction between live and dead stems
Old flower heads can provide some protection to the developing buds below them during winter. In colder or exposed gardens, leave them in place until spring.
How to Prune Mophead Hydrangeas
Mophead hydrangeas produce large, rounded flower heads. They normally need only light pruning.
Step 1: Inspect the Plant
Before cutting, look over the whole shrub. Identify:
Dead flower heads
Healthy pairs of buds
Dead or damaged stems
Weak growth
Crossing branches
Older congested stems
Do not begin by reducing every stem to the same height.
Step 2: Remove the Old Flower Heads
Cut each faded flower head back to the first strong, healthy pair of buds beneath it.
Make a clean cut just above the buds without damaging them.
Avoid cutting much further down the stem unless the stem is dead, damaged or being deliberately removed for renewal.
Step 3: Remove Dead and Damaged Growth
Dead stems can be cut back to healthy wood or removed completely at the base.
If you are unsure whether a stem is alive, lightly scratch a small area of bark. Living tissue is normally green beneath the surface, while dead wood is dry and brown.
Do not damage numerous stems simply to test them. Emerging buds will often provide a clearer indication.
Step 4: Thin Older Stems Selectively
On an established or congested plant, remove one or two of the oldest stems near ground level.
This encourages replacement growth from lower down and gradually renews the shrub without removing its entire flowering framework.
Do not remove all the old stems in one season.
How to Prune Lacecap Hydrangeas
Lacecap hydrangeas have flatter flower heads, with small fertile flowers in the centre surrounded by larger decorative florets.
Their pruning requirements are broadly similar to mophead hydrangeas.
In spring:
Remove old flower heads
Cut back to a healthy pair of buds
Remove dead or damaged stems
Thin a small number of older stems if congested
Retain the main established framework
Lacecaps often have a lighter, more natural shape than mopheads. Avoid excessive shaping that turns the plant into a rigid mound.
How to Prune Hydrangea aspera
Hydrangea aspera develops large leaves and broad lacecap-style flowers. It can become a substantial shrub and usually needs minimal pruning.
In spring:
Remove dead flower heads
Cut out frost-damaged shoots
Remove dead or crossing stems
Thin selectively where the centre is congested
Avoid reducing the entire plant unnecessarily
A mature Hydrangea aspera needs sufficient space to develop its natural form. Repeatedly cutting it back to fit an unsuitable position can reduce flowering and spoil its shape.
How to Prune Oak-Leaved Hydrangea
Hydrangea quercifolia is grown for its oak-shaped foliage, summer flowers, autumn colour and attractive bark.
It generally needs little routine pruning.
In spring:
Remove dead flower heads where required
Cut out damaged or dead growth
Remove badly placed crossing stems
Thin only when the shrub becomes congested
Avoid hard annual pruning
Its branch structure and peeling bark contribute to its winter appearance, so indiscriminate pruning can remove some of its ornamental character.
Pruning Young Group 4 Shrubs
Recently planted shrubs need time to establish.
During the first few years, pruning should normally be limited to:
Removing dead material
Cutting out damaged stems
Removing badly crossing shoots
Lightly improving the shape
Deadheading where appropriate
Avoid hard pruning a young plant simply to encourage growth. Root establishment and consistent watering are usually more important during this stage.
Pruning Established Shrubs
An established Group 4 shrub can gradually become congested, particularly if no older stems have ever been removed.
Selective renewal helps maintain a balanced framework.
Each spring:
Remove the previous season’s flower heads.
Remove dead, diseased and damaged growth.
Identify the oldest or least productive stems.
Remove one or two of these near ground level.
Retain the healthy younger and middle-aged stems.
Step back and check the overall balance.
Gradual renewal is safer than removing most of the plant in one session.
Renovating an Overgrown Hydrangea
An old or badly overgrown hydrangea may need more substantial renovation.
Hard pruning may produce vigorous new growth, but it can substantially reduce or eliminate flowering for at least one season.
Where possible, renovate gradually over two or three years:
First Year
Remove approximately one-third of the oldest and least productive stems near ground level.
Second Year
Remove another portion of the remaining old growth, provided the plant responded well during the previous season.
Third Year
Complete the renewal by removing the remaining unproductive older stems while retaining the strongest replacements.
This staged method maintains some structure and gives the plant time to recover.
A weak, drought-stressed or poorly established shrub may not respond well to major renovation. Improve its growing conditions before carrying out extensive pruning.
Common Group 4 Pruning Mistakes
Cutting Every Stem Down Hard
This may remove much of the established flowering wood. The plant may produce vigorous leaves and stems but few flowers.
Pruning in Autumn
Autumn pruning removes the old flower heads that can provide some protection to the buds below. It also exposes new cut surfaces before winter.
Treating Every Hydrangea Alike
Hydrangea paniculata and Hydrangea arborescens are pruned differently from mophead and lacecap forms.
Removing All Older Wood
Some selective renewal is useful, but stripping out the whole established framework at once can drastically reduce flowering.
Leaving Dead Stems Indefinitely
Dead and damaged stems should be removed cleanly. They add congestion and can make it harder to assess the healthy structure.
Pruning Without Identifying the Plant
Different hydrangeas flower on different types of growth. Confirm the species or cultivar before carrying out hard pruning.
Cutting Into Buds
Make each cut just above a healthy pair of buds. Leaving an excessively long section of stem above the buds creates a dead stub, while cutting too close can damage the new growth.
What Tools Should You Use?
For most Group 4 pruning, you will need:
Clean, sharp secateurs
Loppers for thicker older stems
A pruning saw for substantial woody stems
Gloves
Eye protection where branches are dense
Clean tools make more precise cuts and reduce the risk of transferring disease between plants.
Check that cutting blades are sharp before starting. Crushing or tearing stems creates a larger damaged area than a clean cut.
What to Do After Pruning
After pruning:
Remove the cut material from around the plant
Check the soil for compaction
Apply an appropriate general-purpose feed if needed
Mulch the root area with organic matter
Keep mulch away from direct contact with the stems
Water during prolonged dry conditions
Monitor new growth for late frost damage
Pruning stimulates growth, but the plant still needs suitable soil, water and light to develop properly.
Hydrangeas prefer soil that retains moisture while allowing excess water to drain. They can suffer where the roots are allowed to dry repeatedly.
Pruning in North West Gardens
North West England often experiences high rainfall, but this does not remove the need to check soil moisture.
Shrubs planted close to walls, beneath roof overhangs or under mature trees may remain surprisingly dry. Wind can also increase moisture loss from exposed plants.
Spring growth may start later in elevated or exposed areas than in sheltered gardens around Manchester, Liverpool or lower parts of Lancashire and Cheshire.
Use the plant’s growth and the local weather as your guide rather than pruning every garden on the same date.
Group 4 Compared With Other Pruning Groups
Group 4 is easily confused with several other groups.
Group 2
RHS Pruning Group 2 includes early-flowering shrubs that are generally pruned after flowering.
Group 5
RHS Pruning Group 5 covers certain deciduous shrubs that flower in winter or spring and require a different pruning approach.
Group 6
RHS Pruning Group 6 includes shrubs that flower on new growth produced during the current season. These can often be pruned more firmly in spring.
Group 10
RHS Pruning Group 10 covers pruning methods for many evergreen shrubs.
The flowering season alone is not enough to determine the pruning group. You must also know whether the flowers are carried on old or new growth.
Frequently Asked Questions
When should I prune Group 4 shrubs?
Prune them lightly in spring, when healthy buds and new growth are becoming visible. In exposed or frost-prone gardens, wait until the risk of severe frost has reduced.
Should I deadhead hydrangeas in autumn?
In colder or exposed gardens, leave the old flower heads in place over winter. They can provide some protection to the developing buds below. Remove them during spring pruning.
How far should I cut back a mophead hydrangea?
Cut each old flower head back to the first strong pair of healthy buds. Do not shorten every stem severely unless renovation is genuinely required.
Why has my hydrangea stopped flowering?
Possible causes include hard or badly timed pruning, frost damage, drought, excessive shade, an unsuitable position or removing the developing flower buds.
Can an overgrown hydrangea be cut to the ground?
Some hydrangeas may recover, but hard pruning is likely to sacrifice flowering and can place the plant under considerable stress. Gradual renovation over two or three years is normally safer.
Should Hydrangea paniculata be pruned like a mophead?
No. Hydrangea paniculata flowers on new growth and can generally be pruned more firmly in spring. It is normally treated under Group 6 rather than Group 4.
Do young hydrangeas need pruning?
Newly planted hydrangeas normally need little pruning beyond removing dead or damaged material. Concentrate on establishment, watering and maintaining suitable soil conditions.
Should I remove weak shoots?
Weak, damaged or badly positioned shoots can be removed. However, avoid thinning a young or sparse shrub excessively.
Before You Start Pruning
Confirm the complete name of the shrub before cutting it. If you cannot identify the plant, wait until its leaves and flowers make identification easier.
The safest Group 4 approach is generally light spring pruning: remove old flower heads, dead material and a limited number of congested older stems while retaining the healthy flowering framework.
You can find additional general guidance through the Royal Horticultural Society’s shrub resources.
For help planning, planting or maintaining a garden in North West England, contact Landscaping Emporium.