Japanese Wisteria Brings Late Spring Beauty to the Seattle Japanese Garden
By Corinne Kennedy
Japanese wisteria (Wisteria floribunda) is a late May highlight of our Seattle Japanese Garden. It flowers with long, showy clusters (known as racemes) of many small, lightly fragrant pinkish-violet flowers. This vigorous woody vine was planted over 50 years ago on a pergola near the port village area at the north end of the garden. Because it blooms in the weeks before spring transitions to summer, the Japanese sometimes refer to it as “the plant of two seasons.”
Wisteria is an ancient genus in the pea family (Leguminosae), dating from the Miocene Period (7 to 26 million years ago). Most species of Wisteria are native to eastern Asia, but two species originated in eastern North America. The Japanese species was introduced to the U.S. in 1862. Our garden’s wisteria, recorded as Wisteria floribunda and probably grown from seed, was planted here over a century later. Fuji, or Noda Fuji, is the Japanese name, and Wisteria the botanical name of the genus. It was given to honor a Professor of Anatomy at the University of Pennsylvania, Dr. Caspar Wistar (1761-1818), and in older references is sometimes spelled Wistaria.
Of the several Asian species, Japanese wisteria & Chinese wisteria became the most popular in the West -- because of their profuse bloom, their large flower clusters, and the reliable fragrance and colors available in the cultivated varieties (cultivars). According to Peter Valder (author of Wisterias: A Comprehensive Guide, 1995), Japanese wisteria is the more decorative plant:
“With its many-flowered racemes, it remains in bloom longer, its growth habit is more graceful, the disposition of its blossoms and foliage more elegant, and its autumn colour more effective.”
Wisteria floribunda is native to Japan in the mountains and hills of Honshu, Shikoku and Kyushu. It grows within and on the edges of woodlands, in areas with light shade, and has been cultivated in Japan for over 1200 years. Individual plants may reach 100 years of age -- or even older. It was mentioned in ancient Japanese literature and praised for its beauty, beginning with the Kojiki (translated as Records of Ancient Matters), compiled in 712 from oral traditions. Because of the purple coloration of the flowers, it was originally associated only with the nobility – notably, the powerful Fujiwara clan of the Heian era (794–1192).
With the passage of time, Japanese wisteria came to be associated with all classes of society, not just the nobility. Long-lived, it represented longevity, fertility and love -- and became a favorite decorative motif, represented in art, poetry and other aspects of Japanese culture. By the Edo period (1603-1868), many wisteria-viewing sites had been established, especially near Kyoto and Edo (now Tokyo). This tradition of wisteria viewing has endured to the present day. Like the ritual of cherry-blossom viewing, it is a form of hanami (flower viewing). Famous sites include the Ashikaga Flower Park, the Kawachi Fuji Garden and the Kameido Tenjin Shrine.
Wisteria floribunda is a deciduous woody vine that grows vigorously, climbing in a clockwise direction – unlike Chinese wisteria, which grows counterclockwise. With its strong twining branches, it will eventually reach the tops of trees. With time, the trunk becomes very stout, and the entire plant extremely heavy, causing damage to the plant or structure that supports it. To prevent this, training wisteria on a sturdy pergola or arbor capable of supporting its weight is highly recommended. In Japan, this treatment did not develop until the late 17th century.
Japanese wisteria is hardy to USDA Zone 5 (minimum temperature -20 to -10 degrees F), and grows best in full sun – in moist, deep, fertile soils of variable pH. Plants growing in the wild show considerable variation, but the following characteristics are typical. The compound foliage emerges pale green or bronze-green, maturing to a brighter mid-green. The silky leaves grow alternately on the stem, with each compound leaf consisting of 13-19 leaflets. The smooth gray bark becomes picturesque with age. Old trunks are often described as “fluted and muscle-like”. The showy flower racemes, in shades of violet, range in length from 8 to 20 inches – and occasionally much longer. Individual flowers open sequentially from the raceme’s base to its pendulous apex. Scientists in 1988 succeeded in isolating 120 volatile compounds from the flowers, but fragrance is variable in seedling plants. Leaves turn shades of yellow in autumn. Fruits are pendulous, velvety “pea-pods,” about 4-6 inches long. Changing to a brownish color in October, they persist through winter. Named cultivars have been known in Japan for hundreds of years, and new ones are still being introduced. W. floribunda ‘Macrobotrys’ is an ancient, well-known cultivar with very fragrant flowers and racemes that are exceptionally long (2 to 4 feet).
In addition to differences in fragrance, flower color and raceme length, seedling wisterias differ from cultivars in the length of time needed for plants to begin flowering. Cultivars vary, with some flowering when very young, but seedling plants generally take 10 to 15 years to initiate bloom. For this reason, gardeners interested in purchasing a wisteria are advised to choose a cultivar rather than an unnamed seedling plant. To encourage blooming, plant wisteria in well-drained soil in full sun, and use a low-nitrogen, high-phosphorous-and-potassium fertilizer. Root-pruning an established plant -- using a spade to sever the roots in a circle about 18 inches from the trunk – may also help.
Because wisteria is such a vigorous plant, it should be pruned at least three times annually. Peter Valder states that Japanese wisteria requires more careful pruning than the Chinese species:
“What seems to be most important with this species is that any major thinning and reshaping should be done at the end of flowering, and that thereafter all new shoots are shortened back to two or three leaves and not removed completely. This usually involves a major pruning in late spring after the first new growths have appeared, another much less arduous one about six weeks later, followed by a tidying up of the few long shoots produced subsequently so that the plants look neat for the autumn… They are then particularly attractive when their leaves begin to turn and the pods hang gracefully below. By then they should have a good strong framework with abundant short lateral shoots bearing dormant flower buds.”
Like Laburnum, another vine in the pea family, Wisteria has seeds that are poisonous, especially to children and pets. Other plant parts also contain the toxic saponin wisterin, but it’s not known whether the concentration is high enough to cause injury or death. Rather surprisingly, wisteria seeds and plant parts were eaten and used in traditional Chinese medicine. These practices were not traditional in Japan.
Before carpentry tools were invented, the tough shoots of Japanese wisteria were used to make the ropes used in house construction. The bark was woven into cloth. Flowering stems were cut for ikebana (the ancient Japanese art of flower arranging), a usage that continues to the current day. The heavy vines are grown on pergolas, trained in the form of trees (known as standards), and used for bonsai. Old houses surrounded by wisteria hedges in the shape of swimming dragons are still to be found in some areas of Japan.
Although the pergola that supports it needs periodic renovation, the Seattle Japanese Garden’s wisteria endures, its trunk growing thicker with each passing year. It’s fitting that the posts and other parts are replaced with wood salvaged from our garden or other Seattle parks, and that the SJG gardeners and carpentry crews tend skillfully to both vine and structure. They create and maintain an enduring beauty -- a gift to everyone who works in, supports and visits our garden.
Corinne Kennedy is a Garden Guide, frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.