JARS v47n1 - Plant Portrait: Rhododendron quinquefolium

Plant Portrait: Rhododendron quinquefolium
Nickolas Nickou
Branford, Connecticut

One of the more graceful deciduous rhododendrons is the cork azalea from Japan - Rhododendron quinquefolium . There it grows wild in thickets of small 15- to 20-foot trees, but in cultivation it is usually a medium sized shrub taking 10 or more years to develop the corky bark and to bloom regularly. Many losses occur in the seedling stage which probably explains its scarcity. Once established there are few troubles encountered.
As I don't know of any flowering plants except for mine, all observations are based on the study of my two plants. The largest is about 35 years old and is 8 feet high and 9 feet wide. The smaller, younger plant is about 6 feet high and is more vigorous and upright as it's in a richer, moister soil. Both are on slopes in high oak shade. They bloom regularly each year, but as it rarely goes below 0°F it is difficult to assign a hardiness rating for colder areas. The soil here freezes in winter two or more feet deep. The hardiness zone is 6B, although I have some zone 7 plants in selected sites.

R. quinquefolium
R. quinquefolium in the Nickou garden.
Photo by Nickolas Nickou

Rhododendron quinquefolium is in the Schlippenbachii subseries, and its closest relative is R. pentaphyllum - in many ways a look-alike with bright pink flowers. It occupies similar areas of Japan. R. pentaphyllum is brighter from a distance and usually has similar leaf markings on emerging. A white form does exist. Late in the season it can be easily distinguished from the cork azalea by the smooth trunk and persistence of prominent cilia on the margins of the leaves and petioles.
The cork azalea bears white, campanulate flowers with green flecks in the throat. They are partly hidden by the emerging leaves which are themselves quite attractive. The leaves are in whorls of five and each leaf has a purplish-red margin which disappears in a short time. On the whole it's best to view this plant up close to appreciate its beauty. It's not an eye-catcher from afar as is R. albrechtii .
Plant R. quinquefolium on a slope above a path to appreciate all its attributes: bark, graceful form, leaves and flowers. As R. quinquefolium is so slow to get going I would urge young members to get started now from seed or purchase plants if available.

Nickolas Nickou, MD, is a member of the Connecticut Chapter and spoke on Rhododendron quinquefolium at the Northeast Regional Conference in 1991.