JARS v51n3 - Watts With the Species: R. williamsianum

Watts With the Species: R. williamsianum
Lynn Watts
Bellevue, Washington

One of the most outstanding and most admired of the Rhododendron species, R. williamsianum , grows as a compact mound of bright green. Rhododendron williamsianum needs plenty of sunlight if it is to flower profusely; indeed it should be grown in full sun to maintain its delightful compact nature and to delay its flowering period until danger of frost is past.

Rhododendron williamsianum was first discovered by E.H. Wilson in 1908 at Wa-shan in western Sichuan Province, China. Wilson's original reports indicate the plant as being limited in quantity and distribution in this region. Wilson found these plants at an elevation of 9,180 feet growing on the face of a cliff. Because of the very mild climate from which R. williamsianum was originally collected these plants are of limited hardiness (-5°F), perfectly suited for Pacific Northwest gardens but somewhat more marginally hardy in gardens in the Eastern United States.

Although there are several other round leafed rhododendrons, R. williamsianum is unlikely to be confused with any of these because of its other distinctive characteristics. As stated earlier, if grown in the sun R. williamsianum will assume a dense, compact growth habit. The bronze leaves of its new growth have been described as bright new copper pennies. These copper-colored new leaves gradually turn green as the chloroplasts do their thing. The soft pink bell-shaped flowers which are born in pairs or groups of three on moderately long pedicels hang loosely over this bright green compact mound. Closer inspection reveals the setose hairs on the leaf petioles and on the style of the flowers.

Rhododendron williamsianum Rhododendron williamsianum
R. williamsianum
Photo by Art Dome
R. williamsianum
Photo by Art Dome

As mentioned earlier, this species does tend to be susceptible to frost damage, as it occasionally flowers before the last frost is past. This is more likely to occur if the plant is grown in a shady location.

Rhododendron williamsianum has been used extensively in hybridizing and rightfully so because it passes on its charming characteristics to its progeny.

Here in the Pacific Northwest, R. williamsianum will eventually reach a height of 5 to 8 feet with an even greater spread. Some forms seem to be more free flowering than others, and the so-called Feng form which we obtained from Albert DeMezey of Victoria several years ago appears to flower at the earliest age.

Rhododendron williamsianum leaf White flowered Rhododendron
Close-up of leaf of R. williamsianum
Photo by Art Dome
White flowered R. williamsianum
Photo by Art Dome

H.H. Davidian in Volume III of The Rhododendron Species identifies three distinct forms of R. williamsianum : Form 1,  a small or large rounded shrub; Form 2,  a dome shaped shrub 3 to 4 feet in height; Form 3, a dwarf spreading shrub. Because R. williamsianum responds so readily to the influence of differing sites and climatic variations it is conceivable that these three forms represent single form variability within the species.

If you have R. williamsianum in your collection you already know what a delightful gem it is. If, however, you are one of the few collectors who are not so blessed then don't put off the pleasure any longer. Hurry out tomorrow and find the largest and best looking R. williamsianum and add it to your species collection. You will have added a real treasure to your garden - one that you will enjoy for years to come.

Lynn Watts, a member of the Seattle Chapter, is ARS Western Vice President.