Rhododendron ‘Unique’ Has Lovely Ivory White Spring Flowers
BY CORINNE KENNEDY
The elegant ivory white flowers of Rhododendron ‘Unique’, opening from pale salmon-pink buds. (photo: Alex Monk)
The Seattle Japanese Garden contains many “true” rhododendrons as well as azaleas (shrubs also in the genus Rhododendron). One of my favorites is Rhododendron ‘Unique’, which has long been popular in the Pacific Northwest. It has very attractive evergreen foliage and charming ivory white flowers that open from pale salmon-pink buds.
Unlike both evergreen and deciduous azaleas, the plants we recognize as “true” rhododendrons were not traditionally planted in the gardens of Japan. When the Seattle Japanese Garden was built, however, the broadleaf evergreens so important in Japanese gardens were not available in our region. Fortunately, Jūki Iida, the landscape designer who supervised the Garden’s 1960 creation, recognized that rhododendrons were popular here and decided that they could serve as substitutes. Those chosen included not only large-growing shrubs with showy flowers in large trusses but also much smaller shrubs, with smaller leaves and flowers, that are often mistaken for azaleas.
‘Unique’ is a relatively large-growing rhododendron cultivar with medium-sized flowers and foliage. Nine* are planted in the Seattle Japanese Garden, all located east of the Garden’s central pond and its eastside path. They were likely planted at least several decades after the Garden’s creation. [The Washington Park Arboretum has detailed records of the rhododendrons and azaleas planted in the Garden during the 1960s and early 1970s, but records do not exist for ‘Unique’ and most later plantings.]
Similarly, the history of this lovely plant’s creation isn’t fully known. It was developed by British hybridizer W. C. Slocock and received the English A.M. (Award of Merit) in 1934, but all we know is that it was hybridized sometime before 1934. Only one of its parents was recorded—Rhododendron campylocarpum, a species noted for its delicate, graceful flowers.
Two plants of Rhododendron ‘Unique’ are located near the Garden’s eastside path, in Area G. (photo: Aleks Monk)
Fortunately, ‘Unique’ remains readily available in the Pacific Northwest—and has been described as an “all-time favorite” in the U.S. as well as in the British Isles. I’m impressed that unlike many rhododendron hybrids developed in the early twentieth century, it has very attractive foliage as well as beautiful flowers. The oblong leaves are smooth, rounded, medium green, and about 3 inches long. Well-grown plants bloom profusely and have a compact, rounded, densely foliaged habit, to about 4 feet tall and wide in 10 years. Plants are hardy to USDA Zone 6b (minimum temperature -5 degrees Fahrenheit).
Dense, dome-shaped trusses consist of up to 14 funnel-shaped flowers, opening in April or early May from pale salmon-pink buds. Their color has been described as “ivory flushed with pink, yellower in the throat.” Because of the subtle contrast between the white flowers and pink buds, plants with both unopened buds and fully open flowers are particularly attractive. By peak bloom, though, the flowers have become almost completely white, having lost their pinkish blush.
It's important to recognize that plants continue growing, becoming much larger than their “10-year size.” Over time, some areas of the Seattle Japanese Garden have become very crowded and densely shaded. As a result, many of its ‘Unique’ rhododendrons have lost their typically dense, compact habit.
Rhododendron ‘Unique’ has one major drawback; it’s somewhat susceptible to rhododendron powdery mildew—a different, more serious, disease than the type of mildew most gardeners are familiar with:
“Powdery mildew on rhododendrons is a fungal infection of the leaves. On rhododendrons, the disease often fails to develop the distinctive powdery white growth normally associated with powdery mildews. Leaves may display yellowish-green or purplish-brown spots or blotches on the upper surface. Lower leaf surfaces may show brown or purple areas of various shapes and sizes. This disease may cause extensive leaf drop and even death of very susceptible plants. Powdery mildew is more severe on shaded plants and is favored by the high humidity found in crowded plantings and damp locations.” (from an article on WSU Extension’s online Hortsense website)
Well-grown, unstressed plants are much less susceptible. Plant ‘Unique’ in moist, well-drained, organic, acid soil—in a little shade but with adequate spacing, good air circulation, and regular irrigation during our dry summers. Avoid sites with reflected heat from structures or pavement. Remove fallen leaves throughout the year.
A note for plant geeks: It turns out that Rhododendron ‘Unique’ is not truly unique. The cultivar ‘Bruce Brechtbill’ appears identical to ‘Unique’ in flower size and shape, foliage, and habit—that is, until its flowers open pink, not white:
“The 'Bruce Brechtbill' rhododendron originated at Brechtbill’s Nursery in Eugene, Oregon. In about 1966, a single plant of 'Unique' at the nursery was discovered by Mark Bloom, now of Bloom River Gardens, to have pink, rather than the characteristic cream-white flowers. Bruce Brechtbill, the owner of the nursery, then propagated this sport. He died in 1973 and in the following year the new selection was submitted for registration under the name ‘Bruce Brechtbill’ in honor of the late nurseryman.” (Oregon State Landscape Plants, online database)
For gardeners able to maintain the excellent growing conditions that they require, both rhododendron cultivars, ‘Unique’ and ‘Bruce Brechtbill’, will prove to be lovely additions to the garden.
*Postscript—as is true of gardens everywhere, the Seattle Japanese Garden is always changing. Until very recently, it held ten ‘Unique’ rhododendrons, including three planted in a row and growing together, in Area G. In March, however, the southernmost plant failed from disease and was removed. Two others, prominent in the photo above, remain.
Corinne Kennedy is a Garden Guide, frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.