Royal Azalea, a Fragrant Spring Beauty

By Corinne Kennedy

One of nine royal azaleas in the Seattle Japanese Garden, most planted on the east side of the Garden’s central pond. (photo: Aleks Monk)

The elegant simplicity of Rhododendron schlippenbachii, known as royal azalea, makes it especially appropriate for gardens influenced by Japanese aesthetics, including the Seattle Japanese Garden. This deciduous azalea received the British Award of Merit in 1896 and is considered by many experts to be one of the finest azalea species. Visitors to our Garden will find eight mature shrubs on both sides of the main path along the pond’s eastern side. One additional, much younger shrub was planted in 2011 in the Garden’s mountain area, near the teahouse garden (roji).

Royal azalea is native to Korea, the Korean archipelago, Manchuria, and the Russian Far East, but probably not Japan; authorities disagree on this point. It is very common in Korea, where it forms the dominant understory shrub in open woodlands on the lower slopes of mountains—and is celebrated in royal azalea festivals every spring.

In his book If I Were to Make a Garden, the English plant explorer Ernest Henry Wilson recalled a trip to Korea, where he viewed “the wonderful sight of mile upon mile of drifts of purest pink …. Through thin woods of oak with gray and rose-tinted unfolding leaves, I have walked for hours among myriad blossoms of this beautiful Azalea.”

Royal azalea is known in Japan as kurofune tsutsuji (“foreign ship”), having been transported there at an early date. In fact, it was known and cultivated by the Japanese before the writing of Japan’s first book about azaleas, Kinshu Makura (translated as A Brocade Pillow), published in 1692. The author, Itō Ihei, comments that royal azalea’s flowering branches were used in ikebana and considered “very elegant for this purpose.” It may have been introduced from China, rather than Korea, since it is also known in Japan as kara no tsutsuji, which means “Chinese azalea.”

The history of Rhododendron schlippenbachii in the West began in 1854 with its discovery on the shores of northeast Korea by a Russian naval officer, Baron A. von Schlippenbach—hence the unwieldy species name. It was introduced to the British Isles in 1893 from plant material collected in a Japanese garden. In 1905, it was introduced to the U.S. by the Arnold Arboretum, from seed collected in Korea. Finally, between 1930 and 1936, it was reintroduced here by the U.S.D.A. Plant Introduction Station, from seeds received from Japan and Wales.

In its native woodlands, royal azalea becomes a large shrub and develops an upright, open habit, to about 15 feet tall. In cultivation, particularly in areas with more morning sun, it usually grows to about four feet tall in 10 years, and six to eight feet tall at maturity, with a dense, more rounded habit. It is very hardy, to at least USDA Zone 5 (minimum temperature -20 degrees Fahrenheit), and is particularly suited to areas with cold winters, such as parts of eastern North America, but also does well in the Pacific Northwest. Plants grow best in dappled sun or high open shade, and in moist, well-drained, slightly acidic, humus-rich soil enriched with additional calcium.

The deciduous, egg-shaped leaves are relatively large and very distinctive, appearing in whorls of five at the stem tips. The thinly textured leaves will burn if not given protection from the afternoon sun. In open shade, autumn transforms them into fiery shades of yellow, orange and crimson.

Royal azalea flowers. (photo: Kathleen Smith) 

In April, royal azalea is graced with lightly fragrant, saucer-shaped flowers, 2 ¼ to 3 inches wide, opening as the leaves expand. Held in loose clusters of three to six, they are pale to rose pink (or sometimes white), often with reddish-brown flecks. They contain ten stamens instead of the five stamens characteristic of most azaleas. Plants grow slowly and may not flower until they are five or six years old. Their dry seed capsules are retained for several years. The species grows easily from seed but is reported not to hybridize with other azalea species. 

With their long history of breeding azaleas for diverse flower colors and patterns, the Japanese have developed several royal azalea cultivars—white-flowered as well as compact, dwarf forms. Although these forms are likely available only in Japan, Rhododendron schlippenbachii, and its deep pink cultivar ‘Sid’s Royal Pink’ are available from local or online nurseries here in the U.S.  

Rhododendron schlippenbachii is truly a four-season plant, with its purity of flower, leaf, and form. In the Seattle Japanese Garden, its pale spring flowers and brilliant fall foliage are very much at home. 

[This is a slightly expanded adaptation of my original blog article, posted on March 27, 2015.] 

Corinne Kennedy is a Garden Guide, a frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.