RHS Pruning Group 6: Summer and Autumn-Flowering Shrubs

RHS Pruning Group 6 covers deciduous shrubs that flower from midsummer into autumn on growth produced during the current year.

These plants generate new shoots during spring and develop flowers towards the ends of those shoots later in the same growing season. They can therefore be pruned firmly during spring without removing that year’s flowers.

The basic Group 6 principle is:

Flowers on this year’s growth mean pruning during spring.

Which Plants Belong to RHS Pruning Group 6?

Typical Group 6 plants include:

• Buddleja davidii – butterfly bush

• Caryopteris – bluebeard

• Hardy Fuchsia

• Salvia yangii, formerly known as Perovskia – Russian sage

• Spiraea japonica – Japanese spiraea

These plants produce their flowers towards the ends of fresh shoots that emerge during the current growing season.

Annual spring pruning encourages:

• Strong new flowering shoots

• A more compact plant

• Larger or more abundant flowers

• Removal of winter-damaged growth

• Better light and air movement

• A balanced framework

• Control of excessive size

Not every plant within the same genus necessarily belongs to Group 6. For example, different Buddleja and Spiraea species can have very different flowering and pruning requirements.

Always confirm the complete botanical name before pruning substantially.

When Should Group 6 Shrubs Be Pruned?

Group 6 shrubs should generally be pruned during early to midspring, once the risk of severe winter weather has largely passed and growth buds are beginning to swell.

In North West England, this will commonly mean March or April, although the actual condition of the plant and the prevailing weather are more important than a fixed date.

Waiting until spring has several advantages:

• Winter-damaged stems become easier to identify.

• Old growth provides some protection during colder weather.

• Developing buds show which parts of the plant remain alive.

• New shoots have the full growing season to mature and flower.

• Fresh pruning cuts are less exposed to prolonged winter conditions.

Avoid completing the main pruning during autumn. This offers little benefit and can leave the remaining framework more exposed to wet and cold weather.

How to Prune RHS Group 6 Shrubs

Begin by examining the plant carefully.

Remove Dead, Damaged and Diseased Growth

Remove stems that are dead, broken, damaged or showing signs of disease.

Cut back to healthy living wood or remove the stem completely where appropriate.

Clean pruning tools before moving between plants, particularly where disease may be present.

Remove Weak and Congested Stems

Remove:

• Thin and weak shoots

• Crossing or rubbing branches

• Badly positioned stems

• Growth congesting the centre

• Stems growing in an unwanted direction

This creates an open framework with sufficient space for healthy replacement shoots.

Cut Back the Previous Year’s Growth

Cut the previous season’s flowering stems back to one or two pairs of healthy buds above the established woody framework.

Healthy Group 6 plants should then produce vigorous shoots from these buds as temperatures rise.

The precise height and severity of pruning will depend on the species, age, condition and intended size of the plant.

Avoid simply cutting everything to an arbitrary height without inspecting the position of healthy buds.

How to Prune Buddleja davidii

Buddleja davidii is one of the most familiar Group 6 shrubs.

If left unpruned, it can quickly become large, woody and top-heavy, with flowers increasingly carried at the ends of long stems.

During spring:

1. Remove dead, damaged and weak stems.

2. Identify the established low framework.

3. Cut the previous year’s growth back to healthy buds.

4. Remove badly crossing or congested stems.

5. Retain a balanced framework capable of supporting new growth.

Established plants can generally be pruned firmly. Strong replacement stems should emerge and produce flowers later that summer.

Young or recently planted Buddlejas should initially be treated more cautiously while their root systems establish.

Not every Buddleja is pruned in this way. Confirm that the plant is Buddleja davidii or another current-season flowering type before cutting it back hard.

How to Prune Caryopteris

Caryopteris flowers during late summer on fresh shoots produced during spring.

Wait until healthy buds become visible and the risk of severe frost has reduced.

Then:

• Remove dead or frost-damaged stems.

• Cut the previous year’s growth back to low healthy buds.

• Remove weak and badly positioned shoots.

• Retain a compact, open framework.

Caryopteris can look late to begin growing in colder gardens, so do not assume that apparently bare stems are dead until the plant has had sufficient time to break dormancy.

How to Prune Hardy Fuchsia

Hardy Fuchsias can experience considerable winter dieback, particularly in cold or exposed gardens.

Wait until new growth begins to appear during spring. This makes it easier to identify which stems have survived.

Remove dead stems and cut living growth back to healthy buds. Where the complete top has died, the plant may still produce vigorous replacement shoots from the base.

Retaining the old stems through winter can provide some protection for the crown.

How to Prune Russian Sage

Russian sage, now generally classified as Salvia yangii, flowers on new shoots during late summer.

During spring:

• Remove weak and damaged growth.

• Cut the old flowering stems back to a low framework.

• Make cuts above healthy buds.

• Avoid damaging emerging basal shoots.

• Remove congested or badly positioned stems.

The remaining framework will support the fresh silvery stems and flowering growth.

How to Prune Spiraea japonica

Spiraea japonica flowers on new growth and can be pruned during spring.

Remove dead and weak stems before shortening the previous season’s growth to healthy buds.

Established plants can normally tolerate relatively firm pruning, which encourages colourful young foliage, compact growth and summer flowers.

Do not apply the same method automatically to spring-flowering Spiraeas. Those flower on older wood and are normally pruned after flowering.

Group 6 Compared With Group 4

RHS Pruning Group 4 is principally concerned with Hydrangeas.

Many Group 4 Hydrangeas, including mopheads and lacecaps, flower mainly on growth produced during the previous year. Hard spring pruning can therefore remove the forthcoming flowers.

Group 6 shrubs flower on new stems produced during the current season. Spring pruning encourages rather than removes their flowering growth.

This distinction is particularly important:

• Mophead Hydrangea: preserve much of the older flowering wood.

• Buddleja davidii: cut the previous year’s stems back firmly in spring.

Looking After Shrubs Following Pruning

Firm spring pruning stimulates vigorous new growth. After pruning:

• Remove cut material from around the plant.

• Apply an appropriate general-purpose feed where required.

• Mulch over moist, weed-free soil.

• Keep mulch away from direct contact with stems.

• Water during prolonged dry weather.

• Monitor fresh growth for late frost damage.

• Provide support where vigorous new stems become top-heavy.

Recently planted shrubs should normally be treated more cautiously. Read our guide to looking after newly planted trees and hedging for general establishment advice.

Check for Nesting Birds

Before pruning a large or dense shrub, inspect it carefully for active bird nests.

If a nest is being built or is currently in use, delay pruning until it is no longer active. This is especially important with mature Buddlejas and other densely branched shrubs.

Common Group 6 Pruning Mistakes

Pruning During Autumn

Autumn pruning exposes the remaining framework to winter weather and removes stems that can help protect the plant’s crown.

Pruning Too Late

If pruning is delayed too far into the growing season, replacement shoots have less time to develop and flower.

Applying Group 6 Pruning to Every Buddleja or Spiraea

Species within these genera have different flowering habits. Correct identification is essential.

Assuming a Frost-Damaged Fuchsia Is Dead

Hardy Fuchsias can regrow from low buds or below ground even where the upper stems have died.

Leaving Too Much Weak Old Growth

Retaining large amounts of weak growth can produce a crowded plant with smaller and less impressive flowering stems.

Frequently Asked Questions

How hard can I prune Buddleja davidii?

An established, healthy Buddleja davidii can generally be cut back firmly to a low framework carrying healthy buds. Young, weak or recently planted specimens should be treated more cautiously.

Can I prune Group 6 shrubs during winter?

It is generally better to wait until early or midspring. The old stems provide some protection, while emerging buds make it easier to identify living wood.

Will hard spring pruning stop the flowers?

Group 6 shrubs flower on new growth produced after pruning. Correct spring pruning should therefore encourage flowering rather than prevent it.

Why has my Buddleja not flowered?

Possible causes include pruning too late, insufficient sunlight, drought stress, poor establishment, excessive feeding or incorrect identification of the species.

Is Hydrangea paniculata in Group 6?

The RHS places Hydrangeas within Group 4, although panicle and smooth Hydrangeas flower on current-season growth and are pruned during spring. They should be covered by the species-specific methods in the Group 4 Hydrangea guide.

The Simple Rule for RHS Pruning Group 6

The easiest way to remember Group 6 is:

Prune during spring to produce fresh shoots that will flower later that same year.

For related pruning advice, read our guides to RHS Pruning Group 3, RHS Pruning Group 4 and RHS Pruning Group 5.