Japanese clethra is a dense, deciduous, oval-shaped flowering shrub in the Clethraceae family native Japan. It is typically found in open mountain forests and disturbed woodland areas. The genus comes from the Greek klethra for alder, which this plant's leaves resemble. The species means with veins barbed or bearded. The shrub matures to 9 feet high by 9 feet wide, although specimens can reach 20 feet. This plant prefers partial shade in moist, lime-free, organically rich, acidic, and well-drained soil but will tolerate full sun. Summer cuttings can be easily rooted and it will spread through suckering to form colonies. Protect new spring growth from later spring frosts. Japanese Clethra produces dropping, fragrant white flowers on the current season's growth in summer into early fall. Glossy, dark green leaves turn bright yellow to red in autumn for good fall color. Dark brown seed capsules persist into winter and the polished, grayish-brown bark exfoliates. Flower spikes are more horizontal and drooping and less fragrant than those of native s ummersweet. This plant has gained the Royal Horticultural Society's Award of Garden Merit This shrub will add 4 seasons of interest to the garden. Plant it along ponds or streams, in small groups or as a specimen. Diseases, Insect Pests, and Other Plant Problems: No significant problems. Spider mites can be a problem in hot, dry sites.
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
Dappled Sunlight (Shade through upper canopy all day) | Full sun (6 or more hours of direct sunlight a day) | Partial Shade (Direct sunlight only part of the day, 2-6 hours)
Soil texture
High Organic Matter; Loam (Silt)
Soil pH
Acid (<6.0); Neutral (6.0-8.0)
Soil drainage
Good Drainage | Moist
NC region
Coastal; Mountains; Piedmont
Mature size
Height: 10 ft. 0 in. - 20 ft. 0 in. | Width: 10 ft. 0 in. - 15 ft. 0 in.
Growth rate
Rapid
Maintenance
Medium
Canopy layer
2 - Understory (15-40 ft)
Form & Appearance
Habit / form
Dense; Erect; Oval; Rounded
Texture
Medium
Foliage
Deciduous
Leaf color
Gold/Yellow; Green
Leaf type
Simple
Leaf arrangement
Alternate
Leaf shape
Ovate
Leaf margin
Serrate
Leaf feel
Glossy
Leaf value
Showy
Leaf size
3-6 inches long
Hairs present
No
Leaf detail
This plant has simple, sharply serrated, lustrous, and dark green leaves which are 2 to 5 inches long and tend to be clustered at ends of branches. The leaves are bronze-red to maroon in the fall.
Fall color
Brown/Copper; Red/Burgundy
Flower color
White
Flower value
Fragrant; Showy
Flower form
Raceme
Flower size
1-3 inches
Flower detail
Flowers from July into late August. Horizontally drooping, terminal racemes (4 to 6 inches long) hold numerous, pleasantly fragrant flowers.
Bloom time
Fall; Summer
Fruit color
Brown/Copper
Fruit type
Capsule
Fruit detail
Flowers give way to dark brown seed capsules which persist into winter.
Bark color
Dark Brown; Light Brown; Red/Burgundy
Bark detail
Smooth, polished brown to cinnamon bark that exfoliates.
Wildlife & Ecology
Native status
Non-native
Origin
East Asia, China to Japan
Wildlife value
Flowers are very attractive to butterflies and bees.