Family: Ericaceae

Genus: Rhododendron

Subgenus: Hymenanthes

Section: Ponticum

Subsection: Grandia or Falconera

The word “rhododendron” comes from the Greek for rhódon “rose” and déndron “tree.” Certainly, rhododendrons have earned their reputation for their magnificent floral display, and one can be forgiven for thinking of these plants simply as “rose trees.”

I believe that this simple categorization of this spectacular and diverse genus (more than 1200 species) as a floral phenom results in the impoverishment of many a garden. According to Cox’s Guide to Choosing Rhododendrons, Rhododendron falconeri in subsection Falconera deserves the credit for the longest lasting flowers of the genus — up to a month or more. Though impressive, this still leaves us with 11 months of the year looking at foliage alone. For a region in need of visual stimulation for much of the sun-starved year, gardens should be planned and planted more often with attractive and stimulating foliage in mind.

A quick disclaimer: before any rhododendron aficionados begin turning red in the face, I agree that relatively smaller-leafed species such as R. pachysanthum, R. bureavii, and R. mallotum are among the most handsome foliage plants available anywhere. However, it is some of the fine species from the subsection Grandia that I believe deserve more space in the garden as the foliage is not just handsome, but transporting. The sometimes shockingly large and lush leaves evoke other lands and latitudes.

Within the appropriately named subsection, Grandia, the species with the largest leaves are classified. The elephant in the garden is clearly Rhododendron sinogrande. With leaves that can reach 36 inches, no other Rhododendron can go toe to toe regarding awesome foliage. Spectacular new leaves unfurl grey and metallic, becoming a rich bottle-green with silver indumentum.

The leaves are thick and leathery. Rhododendron sinogrande is native to the northeast of the Chinese province of Yunnan, upper Myanmar and southeast Tibet. It was introduced to the west by George Forrest in 1912 after he encountered it in Yunnan.

The ding against this species for the Pacific Northwest is that the hardiness of R. sinogrande is right on the edge of damage. Plants do get more able to withstand drops in temperature as they age, but be prepared to wrap or otherwise protect your investment for years after planting during sudden cold snaps. R. sinogrande is listed as hardy to +10 degrees F, but that may with ideal siting, during an ideal winter. In the wild, plants may reach 40 feet in height, but in cultivation 10 feet is typical. A 3 foot tall specimen can be seen near the top of the creek in Rhododendron Glen (grid 13-7E).

Another species from subsection Grandia is Rhododendron macabeanum, native to NE India, which is also listed by some as hardy to only +10 degrees F, though it is considered by most to be significantly more successful than R. sinogrande in the PNW. The leaves of this species ‘only’ reach about 12 inches long, but this is balanced by being a larger grower, sometimes reaching 30 feet in cultivation. The foliage is shiny green above with white or fawn wooly indumentum below, the new growth emerging densely covered in white wool.

Rhododendron macabeanum was first collected by Sir George Watt on March 9, 1882 on Mount Japvo, Naga Hills, Manipur, Assam. A 15 foot tall specimen accessioned in 1969 lies along the upper trail at the north end of the Dan Hinkley Asian Maple Collection (grid 28-2E). A smaller specimen lies on the south side of the creek in Rhododendron Glen (grid 13-5E). Please be careful to not cross the creek as there are many emergent plants in the area.

A third species from Grandia that delivers beautiful foliage is Rhododendron kesangiae, named after the Queen Mother of Bhutan, Kesang Dorjii Wangchuck. The leaves of R. kesangiae reach 12 inches, are a very dark green with prominent lateral veins and silver-white indumentum underneath. Specimens of this species reach 50 feet tall in the wild. Reports of the hardiness of R. kesangiae vary from 0 to +5 degrees F. A young specimen can be found in Rhododendron Glen (grid 14-6E) along the path that follows the creek.

The species of Rhododendron in the subsection Grandia are all native to southeast Asia, though they blend into our PNW conifer and mixed forests magically. Now is an excellent time to come visit these amazing plants in the Washington Park Arboretum before the distraction of so much color enters the world. The Woodland Garden, The Sino-Himalayan Hillside, Loderi Valley and particularly Rhododendron Glen are all prime locations to enjoy texture, boldness, and grandeur from these fine species as well as many others, sans flowers.