Culture
Easily grown in average, medium to wet soils in full sun to part shade. Prefers part shade and consistently moist, acidic, sandy soils. Soils should not be allowed to dry out. Tolerates clay soils. Tolerates full shade. Promptly remove root suckers unless naturalized look is desired. Propagate by cuttings. Prune if needed in late winter.
Noteworthy Characteristics
Clethra tomentosa, commonly called summer sweet, is a deciduous shrub that is native to damp woods, swamps, wet marshes and stream banks, often in sandy soils, in the southeastern U.S. from North Carolina to Florida west to Louisiana. It is a rounded, suckering, densely-branched shrub that typically grows to 3-6’ (less frequently to 8’) tall. Young shoots and young leaf surfaces are woolly-tomentose. It is noted for producing a mid to late summer (mid-July to September) bloom of sweetly fragrant white flowers which appear in drooping, narrow panicles (racemes to 2-6" long). Each inflorescence has 2-4 flowering racemes. Flowers give way to dark brown seed capsules (1/8" diameter) which may persist into winter. Mature stems have scaly, dark gray to brownish-black bark. Serrate, obovate to oblong, glossy dark green leaves (to 3-4” long) turn variable but generally attractive shades of yellow to golden brown in fall. Flowers are very attractive to butterflies and bees. Semi-evergreen in warm winter climates.
Clethra tomentosa was formerly listed as Clethra alnifolia var. tomentosum, but has somewhat recently been elevated to separate species status. On a comparative basis, the characteristics of Clethra alnifolia var. tomentosum which were primarily considered in changing its listing to Clethra tomentosum include: (1) flowers panicles are longer and more drooping, (2) petioles are consistently shorter, (3) new shoots are woolly, (4) styles are shorter and hairy, and (5) overall growth habit is more spreading.
Genus name comes from the Greek klethra the name for alder of which the leaves resemble.
Specific epithet from Latin means hairy in reference to the hairs found on the leaves and young shoots of this plant.
‘Cottondale’ leaves are more tomentose than the species, thus lending a blue-green cast to upper surfaces and a light green cast to leaf undersides. Flower racemes are longer than those of the species, typically extending to as much as 16” long”. This cultivar was discovered growing in the Florida panhandle and was subsequently introduced into cultivation by Woodlanders.
Problems
No serious insect or disease problems. Spider mites may be a concern in dry conditions.
Uses
Summer sweets are somewhat unique among flowering shrubs because of their ability to bloom in shady locations in late summer when few other shrubs are in bloom. Mass or group in lawns, foundations or shrub borders. Good flowering shrub for shade or woodland gardens. Effective as a hedge. Also appropriate for moist soils along stream banks or pond/water garden peripheries. Also may be naturalized in cottage gardens, wild gardens or naturalized areas. Plant near a patio to enjoy the fragrant late summer bloom. Compact size makes this an ideal flowering shrub for smaller gardens.