Photo: KENPEI, CC BY-SA 3.0 · source

Shrub · Clethraceae

Sweet pepperbush

Clethra alnifolia

In other languages: Clethra (Nederlands) · Cléthra à feuilles d’aulne (Français)

Sweet pepperbush comes from eastern North America, where it grows in damp woods, swamps and along the coast. It is a deciduous shrub of about 2 m that slowly widens by suckers. From July into September it carries upright spikes full of small white flowers with a sweet, spicy scent that drifts through the whole garden on warm days. In autumn the leaves turn golden yellow. Gardeners value it because it flowers late in summer, tolerates shade and wet soil, and draws bees and butterflies. Well-known cultivars are the compact ‘Hummingbird’ and the pink ‘Ruby Spice’ and ‘Pink Spire’.

Caution: It slowly spreads by suckers: give it room or dig out the suckers regularly.

Updated on 9 October 2026

Light
Partial shade or shade
tolerates little sun
Moisture
Normal to wet
must not dry out
Legal basis
Sand, loam or peat
acid
Hardiness
Fully hardy
down to -30 °C
Size
2 m
tall, 1.5 m wide
Flowering
July–September

Key facts
Pruning months	March
Height	2 m
Native to Belgium	No, planted
Good for bees, butterflies and birds	Yes, for bees and butterflies
Poisonous to people and pets	Not known to be poisonous
Flowering	July–September

Identify

Sweet pepperbush: how do you recognise it?

Habit: Upright deciduous shrub, 1.5–2 m tall and about 1.5 m wide, slowly spreading by suckers.
Leaves: Obovate, 4–10 cm, with a toothed edge, fresh green. They appear late in spring and turn yellow to golden orange in autumn.
Flowers: Upright spikes of 8–15 cm at the tips of the new shoots, July to September; white, pink in some cultivars.
Scent: Sweet and spicy, strongest on warm days.
Fruit: Small round capsules that resemble peppercorns and stay on the shrub for a long time.
Roots: Fine and fairly shallow, with suckers: after a few years the shrub forms a wide clump.

Flowering: July–September · Plants: March–April and October–November · Pruning: March

In your garden

Why grow it?

Flowers from July to September, long after most shrubs have finished.
One of the few flowering shrubs for part shade and shade, and it copes with wet soil too.
The strong, sweet scent makes it ideal beside a patio, path or bench.
Bees, bumblebees and butterflies readily visit the nectar-rich flowers.
Golden-yellow autumn colour gives a second season of interest.
Fully hardy and rarely troubled by disease.

Sweet pepperbush: where does it grow best?

Part shade or shade; in sun only if the soil stays moist at all times.
Acid, humus-rich soil: sand, loam or peat. On chalky soil the leaves turn yellow.
Moist to wet: it even tolerates temporarily waterlogged roots, but dislikes drying out.
Ideal beside a pond, in a damp corner or at a woodland edge.
Allow 1.2–1.5 m per plant; in a group, plant 1 m apart.

Light: Partial shade and shade
Soil type: Sand, loam or peat
Acidity: Acid
Moisture: Normal or wet
Size: 2 m tall, 1.5 m wide
Hardiness: Hardy (to -30 °C)

Goes well with

Rhododendron: The same acid, moist soil; it flowers in spring, the sweet pepperbush in late summer.
Hosta: Large leaves at its feet in the same part shade.
Ferns: A fresh green underplanting for a damp, shady corner.
Astilbe: Pink and red plumes in June–August on the same moist soil.
Hydrangea: More summer flowers in part shade; it also likes acid, moist soil.

Maintenance

Sweet pepperbush: when and how to plant it?

Plant in March–April and October–November.

Plant in March–April or October–November, when the ground is not frozen.
Dig a hole twice as wide as the root ball and mix in leaf mould or ericaceous compost.
Set the plant at the same depth as it was in the pot and firm the soil well.
Leave 1–1.5 m between plants.
Water generously straight away and keep the soil moist throughout the first year.
Spread a thick mulch of leaf mould, bark or pine needles around the base.

Care

Watering: It must never dry out: in dry summers give plenty of water every week, especially in the first year.
Feeding: In April, a little leaf mould or organic fertiliser for acid-loving plants. Nothing more is needed.
Mulching: A layer of leaf mould or bark every spring keeps the soil cool, moist and acid.
Suckers: If you don’t want it to spread, dig out the suckers at the edge in spring.
Spent flowers: Leave them: the brown capsules are decorative in winter.

Tip: Plant it next to a patio or path you often use in August: that is where you will enjoy the scent most. Mulch every year with leaf mould to keep the soil acid and moist.

Sweet pepperbush: when to prune it?

Pruning months: March.

When: In March, before the leaves break. It flowers on new wood, so pruning costs no flowers.

How:

Each year, cut one or two of the oldest, thickest stems out at the base to rejuvenate the shrub.
Remove dead, weak and crossing stems.
An overgrown shrub can be cut back hard in March; it will still flower the same summer on the new shoots.
Dig out unwanted suckers at the edge.

Caution: It leafs out late, often not until May: wait to see what sprouts before cutting out ‘dead’ stems.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division: In March or October, dig up a rooted sucker at the edge of the shrub and replant it straight away.
Softwood cuttings: In June–July, take 8–10 cm cuttings from young shoots and root them in moist, acid cutting compost under plastic. They root within a few weeks.
Layering: In spring, peg a low branch into the soil; sever it after a year and replant it.

Sweet pepperbush: how does it get through the winter?

Hardy to −30 °C.

Fully hardy, to about −30 °C: no protection is needed in Belgium.
The small brown capsules stay on the bare shrub through the winter.
In a pot: choose a large pot of ericaceous compost and keep it sheltered; the root ball must not dry out or stay frozen for long.

Diseases and pests

Yellow leaves: Yellow leaves with green veins point to soil that is too chalky (chlorosis). Mulch with leaf mould or pine needles and water with soft water, such as rainwater.
Brown leaf edges: A sign of drought or too much sun. Water generously and mulch thickly.
Spider mite: Fine yellow speckling and webbing under the leaves, mainly in hot, dry summers. Hose the leaves down and keep the soil moist.
Late leafing: Bare branches in April are normal: it does not leaf out until May.

Through the year

January: Dormant. The capsules decorate the bare shrub.
March: Prune: cut the oldest stems out at the base. Plant.
April: Plant. Give leaf mould or organic fertiliser and mulch.
May: The leaves finally appear. Water in dry spells.
June: Take softwood cuttings. Water in dry spells.
July: Flowering begins. Water weekly in dry weather.
August: Full flower and scent. Bees and butterflies on the spikes.
September: Last flowers. Keep the soil moist.
October: Yellow to golden-orange autumn colour. Plant or divide off suckers.
November: Plant. Top up the mulch with fallen leaves.
December: Dormant. The capsules hang on.

Use

Good for wildlife

Bees: Nectar and pollen for honeybees and wild bees.
Butterflies: Nectar for butterflies.

You and this species

Did you know?

The name Clethra comes from the ancient Greek word for alder; alnifolia means ‘with alder-like leaves’.
The name ‘sweet pepperbush’ refers to the dry little fruits, which look like peppercorns.
In the wild its suckers form dense thickets in swampy woods and along the Atlantic coast.

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