The Japanese clethra, Clethra barbinervis, is a good all-rounder, and we have five of these deciduous shrubs scattered around Lady Anne’s Garden and Bicentenary Arboretum. This plant has stunning flaky, patchy bark, fantastic long racemes of small, white, fragrant flowers in late summer, and wonderful red-orange-yellow foliage in the autumn. The seed heads may persist well into the winter, and then in the spring this shrub produces slightly up-curled, deep green leaves. This is a ‘value-for-money’ plant with interest in every season.
Clethra barbinervis originates from wooded hills and mountains, thriving on the side of sunny rides through woodlands as well as dappled shaded areas, all over Japan. This plant is at home in our climate, surviving temperatures down to -17°C one year here at Rosemoor, with no signs of ill effect.
It copes with neutral to acidic soil. It favours a sheltered spot though because it can suffer from wind damage. This shrub may reach 2.5m tall and wide (taller in the wild) within 15 to 20 years given the right conditions, but if size becomes a problem, it is relatively easy to control by light pruning, directly after flowering. Otherwise leave it alone and remove any odd wayward branches as necessary.
It is a great candidate for use in cottage, informal or woodland gardens. This plant seems to be relatively resistant to pests and diseases and the family are said to have some tolerance of honey fungus. The flowers are hermaphrodites (male and female reproductive organs within the same flower) and are pollinated by bees.
The image is of C. barbinervis in the bed behind Rosemoor house which has been pruned to show off its winter bark and to allow light into the under planting during the summer.