Languid summer evenings are a time when the garden becomes a luxurious retreat. The heat of the day slowly fades with the light and the outlines of shrubs and trees take on a restful silhouette, punctuated here and there by the intensified glow of light colored blooms and foliage. The humid air tenderly drapes lush garden fragrances around gardeners who are out and about at the end of the day - an especially delicious reward for an evening stroll (or an extra enticement for that overdue sunset weeding session....). There are many plants that contribute to the sensuality of summer's landscape, among the most delightful of these are the species and cultivars of the genus Clethra .
Clethras are small shrubs to large trees with dark green, very beautiful foliage and the unique attraction of showy flowering in mid-late summer when few other shrubs or trees are in bloom. Some are very fragrant, others have exquisite bark character and all are relatively trouble free, excellent garden plants. They are a tremendously adaptable plants thriving in shade or full sun (which gives best flowering) with almost no pest or disease problems given adequate moisture. They are completely hardy throughout the southeast, from coast to mountains and one, C. alnifolia, is surprisingly salt tolerant - making it an excellent plant for coastal gardens. Propagation of Clethra is quite reliable either from summer cuttings or ripe, dry seed.
Perhaps the best known of the Clethras is Clethra alnifolia, Sweet Pepperbush. Sweet Pepperbush is an aptly named deciduous, native shrub whose small fruits are reminiscent of the dried black peppercorns that stock peppermills, and whose flowers have a deliciously sweet and spicy fragrance. Sweet Pepperbush can be found growing in wet areas up and down the eastern part of the US from Maine to Florida, and west to parts of Texas. It is the most cold hardy of the Clethras discussed here. It is a low to medium sized, rounded shrub reaching 3 - 8 feet in height, with distinctly upright branching whose branches are covered with handsome, glossy, dark green foliage of neat, oval outline. In nature, the plants tend to sucker and develop into quite large, well-defined and attractive colonies. In mid-summer, the ends of the branches are covered in upright clusters of small, white blooms. The shrub appears to develop a beautiful, frilly mantle of cream - and even more wonderful is the fragrance of these blooms that can be a great pleasure even from a distance. In the fall, the leaves turn a handsome, burnished gold and the flowers mature into the black, pepper-like capsules that are attractive in their own right.
There are several notable cultivars of Sweet Pepperbush that make excellent summer blooming garden plants for many uses, from mixed border to specimen to naturalizing. 'Creel's Calico' is among the most spectacular with large splashes and specklings of creamy white on the foliage (but quite new and therefore currently difficult to find in the trade), 'Hummingbird' is an exciting, relatively new form with compact, almost dwarf habit (reaching three feet) and very prolific flowering, 'Paniculata' is an especially vigorous selection with large flower spikes, 'Pink Spires' is a pink flowered form whose buds emerge soft pink and lighten to pale pink as the flowers open, and 'Rosea' develops pink flower buds that open into pinkish-white blooms.
In addition to the well known Clethra alnifolia, there are several other species with equally excellent garden character. Clethra acuminata, Cinnamon Clethra is another eastern North American native found primarily in drier, montain areas. It is slightly larger and more open than C. alnifolia with pendulous flower clusters that are not quite as showy en masse as those of C. alnifolia, but Cinnamon Clethra has the additional wonderful attribute of developing warm, reddish brown, peeling bark on older plants. Clethra barbinervis , Japanese Clethra, is a large shrub or small tree from Japan that gets significantly taller than other forms, reaching upwards of 15-18 feet with age. It has larger, more leathery leaves than its North American relatives and flower clusters are longer and semi-pendulous. The foliage develops striking fall color in rusty red and gold shades and the bark of Japanese Clethra has been compared with that of the magnificent Stewartias with its polished, warm tones and peeling character. Clethra tomentosa, Wooly Summersweet, appears nearly identical to C. alnifolia but it has 'woolly' stems that are covered with a fine down and and a silvery cast to the foliage. It is found only in the southeastern US. Clethra macrophylla and C. pringlei are very rare species from Mexico likely encountered only in arboreta and botanic gardens with hardiness still in the testing stage. They can be found at The NCSU Arboretum (now the JC Raulston Arboretum) where they grow with somewhat larger leaves than other forms and very beautiful lacy flowers.
The different forms of Clethra are all excellent garden plants that bring sparkle and interest to the height of summer, both with fresh flower and spicy scent. Their foliage and bark add exceptional dimension to the garden as well in unexpected ways. At The NCSU Arboretum (now the JC Raulston Arboretum), many different Clethras are important elements in a number of the plantings. Come out to the Arboretum for a mid-summer's evening walk - and wander the paths to find the dreamy flowers and fragrance of Clethra in the garden. br>