upright), the foliage seemed somewhat smaller,
and the bark was exfoliating, revealing interest-
ing patterns of brown and gray.
I’ve since encountered several other species
of Clethra around the Arboretum, including C.
alnifolia, C. fargesii and C. acuminata. And UW
Botanic Gardens curator Ray Larson says that
there have been recent additions of C. delavayi
and C. kaipoensis to the collection. (The genus
comprises about 80 species, native mainly to
East Asia and the Americas.) But C. barbinervis
is easily the most abundant of the bunch here,
making up over half the 30 or so specimens.
Specimens of Japanese sweet shrub
also comprise the oldest of the Clethra in the
Arboretum collection. A grouping of about 10
plants on the lower Lookout Trail—just north of
where it intersects with the path that connects
the new Centennial Garden to Rhododendron
Glen—dates to 1945. These were origi-
nally received as seed from the Royal Botanic
Gardens, Kew and were planted out in 1950.
They are upwards of 20 feet high now. At first,
the plants were misidentified as C. monstachya
(syn. C. delavayi); but in 1963, then-director
Brian Mulligan confirmed them as C. barbin-
ervis, based on their floral characteristics.
Another cluster of interest is located just to
the south of the Asiatic Maple Collection, along
the upper Lookout Trail on the west side of the
Magnolia Collection. This group of four speci-
mens—about 12 feet high—was received as seed
in 1953 and planted out in 1959. The records
indicate that the seeds were provided by noted
UW botany professor Charles Leo Hitchcock,
who collected them in Japan.
Clethra barbinervis is an upright, deciduous
shrub native to open mountain forests of south-
ern China, Japan and Korea. It typically grows
between 10 and 20 feet tall and about half as
wide. It produces two- to four-inch, somewhat
glossy, dark-green, pointed, oval-shaped leaves
with serrated edges. I haven’t gone to see its fall
foliage, but I’ve read it’s good. (The leaves turn
bright yellow, sometimes red.) The plant does
best in partial shade and consistently moist,
acidic soils.
If you’d like a mid-summer flower fix, be
sure to come to the Arboretum. Check out what’s
in bloom in the summer-themed Centennial
Garden, then on your way to see the hydrangeas
in Rhody Glen, stop by the Japanese sweet bush
for a very satisfying sniff. You’ll see other Clethra
flowering in that main cluster, too—and probably
lots of happy bees. m
N iall D unne is the editor of the “Arboretum
Bulletin” and the communications manager at
the Arboretum Foundation.
TOP LEFT: The fragrant flower spikes appear in late July. RIGHT: Colorful peeling bark on a mature specimen.
18 v Washington Park Arboretum Bulletin