New Companion Plants: Clethra Comeback
L. Clarence Towe
Walhalla, South Carolina
Rhododendron enthusiasts are usually interested in a variety of companion plants to contrast with and compliment their favorite shrubs. With their late flowering, fragrance and ease of culture, clethras are a good choice and are gaining in popularity as new selections become available.
Of the 30 or so species referenced in Hortus Third, the most familiar is Clethra alnifolia, sweet pepperbush or summersweet, which behaves much like a deciduous azalea. Small white or light pink flowers on upright or nodding racemes always attract the birds and the bees, and especially the butterflies. Clethra tomentosa, woolly summer-sweet, a similar species with stems and leaves covered with matted hairs, is classified by some taxonomists as a variant of C. alnifolia.
A New Color
A branch sport first spotted on a plant of 'Pink Spires' by nurseryman Andy Brand can best be described as a color break in the species. 'Pink Spires', which some feel is a re-name of 'Rosea', has light pink flowers. The sport has ruby red buds that open to wine flowers and dark green leaves that turn bright gold in the fall. Tentatively named 'Ruby Spice', it is being propagated at Broken Arrow Nursery by Andy and nursery owner and laurel breeder Dick Jaynes.
| Clethra 'Pink Spires', left; Clethra 'Ruby Spice', right.
Photo by L. Clarence Towe
New White Selections
'Hummingbird', found in Georgia by noted azalea and holly expert Fred Galle, is a choice cultivar in all respects. Fred selected the plant for its compactness, heavy flowering and unusually glossy, dark green leaves. It is highly stoloniferous (suckers have been known to escape through drain holes of container grown plants) and forms a low mound that can get to 3 feet tall by 8 feet wide. Though found in USDA Zone 8, it has proven hardy to Zone 5.
'Fern Valley Late Sweet' is a 5 feet tall by 2 feet wide columnar selection found in North Carolina by plantsman Tom Clark. It has small leaves, long, upright racemes and a branching pattern not usually seen in clethras. Blooming in late September and into October, it extends the flowering season of the species by several weeks.
'Ann Bidwell' is a new panicled selection from a seed lot grown by Mrs. John Bidwell of Cotuit, Mass. The plant is somewhat upright and compact, with elongated leaves and short racemes in clusters of five to eight.
'Creel's Calico' appears to be the first selection with variegated foliage. Found near Columbia by Mike Creel, a journalist/botanist with the South Carolina Wildlife Department, the plant has highly variable leaves streaked, dotted and sectored with cream, pastel green and dark green areas. It is being grown by several nurseries but seems to be sensitive to excessive moisture and fertilizer associated with container culture. Good foliage color can be found on unfertilized plants grown in ground in light shade.
New Pink Selections
As a group, pink clethras have pink buds that fade to light pink or white when fully open. Occasionally, probably depending on several factors, a selection may have bright pink flowers some years.
'Hokie Pink' originated as a sport on a plant of 'Rosea' found growing on the campus of Virginia Polytechnic Institute. It has pink flowers similar to 'Rosea' but with a more dense and compact growth habit.
'Fern Valley Pink', again found by Tom Clark in North Carolina, is notable for its long, pendulous pink racemes and heavy fragrance.
Several other species of clethras have ornamental value, both for their flowers and flaky bark. Clethra acuminata, cinnamon clethra, a native of the Appalachian Mountains in several states, has cinnamon colored twigs and bark that occasionally rolls into tight cylinders like stick cinnamon. It and somewhat similar C. barbinervis, Japanese clethra, make interesting specimen plants if grown with the lower limbs removed to expose their attractive bark. Evergreen C. prinqlei, native to the Southwest and Mexico, seems adaptable to the milder areas of USDA Zone 7.
Phil Waldman, owner of Roslyn Nursery, is growing C. barbinervis x C. fargesii 'Summer Sweet', which may be the first hybrid clethra available commercially. It has heavy wood, leathery, dark green leaves resembling those of buckeyes (Aesculus ssp.), and white flowers. It is a well behaved 5-foot shrub with attractive seed pods that give added contrast after the flowers drop.
| Clethra 'Summer Sweet' with seed pods after flowering.
Photo by L. Clarence Towe
Compared to more showy rhododendron and azaleas, clethras probably view themselves as "blue collar" common plants, but they are very easy to propagate and grow and not prone to disease. They prefer damp soil and light shade but will grow in most garden situations. Soft cuttings root quickly under mist and propagation by seeds is the same as for rhododendrons. They respond well to pruning and can be kept to a desired size or shape with little difficulty.
With this widening gene pool, breeding within the C. alnifolia selections or hybridizing between compatible species could lead to interesting new selections. (A "Ruby-spiced Hummingbird" would be nice.) Locating parent plants together in a clethra-free area will provide seeds without the need for tedious hand pollination and, if treated with care, some species will flower the second summer following seed germination in the fall.
The older selections of 'Rosea', 'Pink Spires', 'Compacta' and 'Paniculata' are widely available. The new selections are, or will soon be available from Broken Arrow Nursery, Roslyn Nursery, The Cummins Garden, Transplant Nursery and other nurseries advertising in this Journal.
Mr. Towe, a member of the Azalea Chapter, has also authored companion plant articles on conifers (Fall 1994) and laurels (Spring 1995).