Summersweet

Sun

Full sun to partial shade; tolerates deeper shade but flowers less heavily. Afternoon shade helps in hot climates.

Water

Keep the root zone consistently moist, especially during establishment and hot weather. Tolerates wet soil but is poorly suited to prolonged drought.

Soil

Acidic, humus-rich soil that retains moisture; tolerates clay and sandy soil if moisture is adequate. Alkaline soil can cause yellowing leaves.

Height

5-8 ft (1.5-2.4 m)

Spread

4-6 ft (1.2-1.8 m), spreading wider over time by suckers

Flowers

Midsummer to late summer; fragrant, upright spikes of small white flowers. Some cultivars have pink flowers.

Foliage

Alternate, oval, toothed green leaves, turning yellow to golden brown in autumn. Leaves emerge relatively late in spring.

Growth

Slow to moderate

Care needed

Low

• Water deeply during dry spells; do not let newly planted shrubs dry out.
• Apply 2-3 in (5-8 cm) of leaf mould or composted bark each spring, keeping it clear of the stems.
• Feed lightly in spring only if growth is weak; avoid routine heavy feeding.
• Remove unwanted root suckers at their point of origin if you need to limit the shrub's spread.
• Check soil pH before planting in chalky or limestone areas; choose another shrub if the soil is strongly alkaline.

Pruning. Prune in late winter or early spring, removing dead wood and taking out a few of the oldest stems at ground level if crowded. Flowers form on the current season's growth, so avoid pruning once new shoots are developing.

Late winter

Remove dead or damaged stems and thin congested older growth.

Spring

Plant while soil is moist, water thoroughly and mulch around the root zone.

Late spring

Allow time for the late-emerging leaves before deciding that bare stems are dead.

Summer

Water during dry spells and check leaf undersides for spider mites in hot, dry conditions.

Late summer

Leave spent flower spikes for their brown seed capsules, or remove them for a tidier appearance.

Autumn

Plant or transplant after leaf fall where the soil remains workable; remove unwanted suckers.

• Plant beside a path or seating area where you can enjoy the summer fragrance.
• Group along a damp woodland edge with ferns and shade-tolerant perennials.
• Use in the moist portion of a rain garden, allowing room for suckering growth.
• Combine with winterberry and red-twig dogwood in an informal shrub border for interest across several seasons.

Garden styles it suits: Woodland, Wildlife garden, Pollinator garden, Sensory garden, Cottage garden and New England.

Plant it with: Winterberry, Red-twig dogwood, Cinnamon fern, Royal fern, Virginia sweetspire and Cardinal flower.

Wildlife: The flowers provide nectar and pollen for bees, butterflies and other insects. Dense, suckering growth offers shelter for birds and small animals, and the persistent seed capsules may attract seed-eating birds.

• Drought stress causes wilting, scorched leaf edges and poor flowering; water deeply and mulch, or move the shrub to a moister site.
• Spider mites may cause stippled leaves in hot, dry weather; rinse leaf undersides with water and use insecticidal soap labelled for the plant if needed.
• Yellow leaves with greener veins can indicate alkaline-soil chlorosis; test the soil and move the shrub to an acidic bed if the site is unsuitable.
• Leaf spots occasionally develop in humid conditions; collect fallen affected leaves, improve airflow and avoid wetting foliage when watering.

Not known to be toxic to cats, dogs, horses or people. No part is generally recognised as poisonous, but it is not an edible plant and eating plant material can still cause stomach upset.

• Virginia sweetspire (Itea virginica)

  Its white flower spikes usually arch or droop and appear earlier, in late spring to early summer. Autumn leaves commonly turn red or purple rather than summersweet's usual yellow.

• Japanese clethra (Clethra barbinervis)

  It becomes a much larger shrub or small tree, with conspicuous peeling bark and arching flower clusters rather than summersweet's mostly upright spikes.

Clethra comes from the Greek name for alder, and alnifolia means alder-leaved, referring to the resemblance of its foliage to alder leaves.

Propagation. Lift rooted suckers during dormancy, take softwood cuttings in early summer, or sow seed. Use cuttings or divisions to preserve a named cultivar's characteristics; seedlings may differ from the parent.

Accepted botanical name

Clethra alnifolia

In the US and Canada

Native in Canada and the lower 48 states.

Native range

Alabama, Connecticut, Delaware, Florida, Georgia, Louisiana, Maine, Maryland, Masachusettes, Mississippi, New Hampshire and New Jersey.

Measured

Soil pH 4.5 to 7. Average height 394 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.