Nature on Trail: Pacific Rhododendron
By Sylvia Feder
Rhododendrons, affectionately called “rhodies” by their many admirers, are so ubiquitous in our yards and gardens that many people may be surprised to learn that they are also Northwest natives. Admittedly, the number of varieties we see cultivated are not represented in our woods, but our own Pacific rhododendron is every bit as striking as the cultivars, particularly when seen in its native habitat. At no time is it more spectacular than late spring, when it bursts into bloom, lending splashes of vibrant pink and red to dark green woods.
Rhododendrons as a group consist of over 1,000 species with a worldwide distribution including China, North America, Australia, and Europe. The tallest can be up to 100 feet in height, while the smallest, found in the arctic, hug the ground at just an inch or so tall.
Our own rhododendron is an understory plant, a leggy, sprawling shrub measuring ten to twenty feet in height, reaching upward as it searches for sunlight under its companion coniferous trees. Its scientific name— Rhododendron macrophyllum, was well chosen—the genus name means “rose tree,” and the species name means “large leaves.” These leaves, as any gardener knows, are thick and leathery as adaptations to climate stress. They have the ability to roll inward during dry or cold periods. Hairs on the underside of the leaves protect them from dessication and help insulate them from freezing.
The Pacific rhododendron is found along the coast of Washington and Oregon (giving rise to its other name of “coast rhododendron”), north into coastal British Columbia and south into California. It tolerates dry, but prefers damp soil, and in Washington is found in association with Western red cedar, Western hemlock, and Douglas fir. It co-habitates with salal, Oregon grape, and other understory plants. It typically begins to bloom in late April or May, with the bloom moving up in elevation as the spring progresses. In western Washington, the best place to see native rhododendrons is along Hood Canal and on the Olympic peninsula, where their large bright blooms cheer up the highways and forest trails.
Rhododendron shrubs of both types provide year-round shelter for wildlife, but have relatively little nutritional value due to toxins in the leaves and flowers, which presumably help protect it from mammalian foragers. There are reports that the mountain beaver occasionally snacks on the twigs and flowers, but deer leave it alone. There are reported cases of domestic livestock poisoned by rhododendron leaves.
In 1892, the Pacific rhododendron was chosen as the Washington state flower—over six other contenders—by a group of Washington women who were asked to pick a flower to represent Washington at the 1893 World’s Fair in Chicago. Their selection was formalized in 1959 by the Washington state legislature—a decision applauded by generations of Northwest gardeners, hikers, and other outdoor enthusiasts.There are even cases of humans being sickened by ingesting honey from areas where bees have foraged extensively on wild or cultivated rhododendrons. Called “mad honey,” the symptoms of rhody poisoning include gastro-intestinal upset as well as alterations in heart rate and blood pressure.
Learn more about Pacific Rhododendron at the Burke Museum's Herbarium website.