Summersweet Clethra, Clethra, Summersweet, or Sweet Pepper Bush

(Clethraceae - White Alder Family)

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• Form
  • medium-sized ornamental shrub
  • maturing at about 6' tall by 5' wide, forming tight colonies with age (however, the increasingly predominant cultivar 'Hummingbird' is half this size)
  • upright oval growth habit ('Hummingbird' has a spreading mound growth habit)
  • slow growth rate

• Culture
  • full sun to full shade
  • best performance occurs in partial sun to partial shade in moist to wet, acidic, fertile, organic soils, but it is rather adaptable to a wide range of conditions, including sunny sites, occasionally dry soils, soils of average fertility, soils of various pH, and Winter salt spray
  • cultivars are propagated by rooted cuttings, but the species form may also be propagated by seeds
  • White Alder Family, with no significant diseases or pests
  • often suckers with age to form tight colonies (which is good for naturalized situations)
  • heavy pruning, to remove Winter-killed wood, to promote compactness, or to rejuvenate, is easily accomplished without worry, as flowering occurs on the new growth of the current season

• Foliage
  • medium to dark green, alternate, obovate, serrated, and somewhat late to leaf out
  • fall color is usually a clear golden-yellow and persists for two to four weeks

• Flowers
  • white, shell pink, or light pink, blooming anytime from late July to early September (usually in mid-August), and lasting for about three weeks when in bloom
  • inflorescences are fragrant, fine-textured, upright, about 4" long by 0.75" wide, and bottlebrush-like in appearance, attracting many butterflies and bees and a moderate quantity of hummingbirds
  • inflorescences occur on the new growth of the current season

• Fruits
  • fruiting stalks, having many miniature oval capsules with persistent elongated styles, are noticeable, Winter-persistent, and a good identification feature, but are not considered ornamental

• Twigs
  • light brown to tan, ascending as several stems that are sparsely-branched at the base, but having numerous lateral shoots at the very apex of the new growth
  • shrubs become leggy with age, and often die back at the apical stem tips in Winter
  • shrubs may become stoloniferous (suckering from the roots near the base of the stems) with maturity, forming tight colonies

• Trunk
  • not applicable

• ID Summary
  • most forms consist of an upright oval shrub that becomes leggy with maturity (but mildly suckering with age), having alternate dark green leaves that emerge late, and mid-Summer bottle-brush-like inflorescences that are white to light pink and very fragrant, giving rise to upright peduncles whose fruits transition from chartreuse to brown and remain throughout Winter, having persistent styles

• Function
  • specimen, foundation, group planting, border, or naturalizing shrub

• Texture
  • medium texture in foliage and when bare
  • thick density in foliage and average density when bare

• Assets
  • fragrant, fine-textured inflorescences occur in mid-Summer and attract many butterflies
  • heavy pruning can be accomplished in Spring, as flowering occurs on new wood
  • tolerant of permanently moist to continuously wet sites
  • Winter salt-spray tolerant

• Liabilities
  • legginess occurs with age
  • root suckering with advanced age forms small colonies (this can be an asset if naturalization or moderate erosion control is desired)

• Habitat
  • zones 3 to 9
  • native to the Eastern United States

• Alternates
  • Summer-flowering shrubs (Buddleia davidii, Caryopteris x clandonensis, Itea virginica, Hydrangea species, Philadelphus species, etc.)
  • wet-site tolerant shrubs (Cornus [shrub forms], Hamamelis vernalis, Itea virginica, Myrica pensylvanica, Salix purpurea, etc.)
  • flowering shrubs for shady spots (Calycanthus floridus, Fothergilla gardenii, Hydrangea species, Itea virginica, Pieris japonica, Rhododendron [including Azaleas], etc.)

• Variants
  • Clethra alnifolia 'Hummingbird' - the introduction that has revolutionized this genus, being a truly compact and spreading form that is much less leggy, slowly maturing at 3' tall by 3' wide, with twice as many inflorescences as the species form, and with the inflorescences much more densely arranged in the smaller canopy
  • Clethra alnifolia 'Pink Spires' - inflorescences that are red-pink in bud, opening as a light pink color and not fading
  • Clethra alnifolia 'Rosea' - inflorescences that are pink in bud, opening as a shell pink color and fading quickly to off-white, becoming less common in commerce

• Translation
  • Clethra translates from the Greek as "Alder", which is a type of tree.
  • alnifolia translates as "Alder-foliaged", promoting the very faint resemblance of the slightly obovate leaves to those of the genus Alnus.

• Purpose
  • Summersweet Clethra is a mid-Summer-flowering shrub, preferring moist to wet soils and shady sites.

• Summary
  • Clethra alnifolia is known as a Summer-flowering shrub that readily naturalizes in the border or makes a good foundation shrub, and is excellent for wet sites in partial shade.