Rhododendron macrophyllum (Pacific Rhododendron, Coast Rhododendron or Big Leaf Rhododendron) is a broadleaf evergreen rhododendron species native to western North America. The northern limit of the range of the Pacific Rhododendron is somewhat north of the border between Canada and the US in British Columbia. It is found as far south as Monterey Bay in California. It is mostly coastal in distribution but extends its range eastward to locations in the Cascade Mountains in Oregon, Washington and British Columbia.
It is a shrub growing 2-9 m tall. The leaves, retained for 2-3 years, are 7-23 cm long and 3-7 cm broad. The flowers are 2.8-4 cm long, with five lobes on the corolla; color is usually pink, although variants exist.
This species, like many rhododendrons, thrives in disturbed habitats such as roadside embankments and recently deforested wildlands. The photo at the top of this page was taken in a forest in Oregon that was burnt over just three years before the time of the photo (2005). The rhododendrons in that area, both Pacific Rhododendrons and Western Azaleas, are already regrowing and blooming from the unburnt roots.
The Pacific Rhododendron has been overshadowed horticulturally by the many other rhododendron species that are easier to grow and that have a more pleasing appearance. The shrubs can be scraggly and the flowers are often much less impressive than those of its relatives. Also, it is easy to kill this plant with an excess of summer watering - while not watering it can leave it looking pathetic. In its native range and once established it can be a trouble free attractive plant requiring a minimum of attention.
In recent years it has been the main focus of a study group at the Rhododendron Species Foundation in Federal Way, Washington, the Western North American Rhododendron Species Project (WNARSP). The WNARSP is documenting the detailed range and forms of all of the western North American rhododendron species.