Japanese wisteria

Family

Fabaceae

Habit

Climber

Height

8.5 m

Spread

9 m

Growth

fast

Lifespan

70 years

First yield

after 12 years

Hardiness

zone 5–9

Shade tolerance

full sun

Soil

Sand, Silt, Loam

Soil moisture

semi-dry – very wet

pH

6 – 7

Synonyms

Blauregen, Wisterie

Times apply to the northern hemisphere in a temperate climate and shift with altitude and cultivar.

Edible: Samen – gekocht. Im Feuer gebacken schmecken sie ähnlich wie Kastanien. Vorsicht ist geboten, siehe Hinweise zur Toxizität oben auf der Seite. Junge Blätter – gekocht. Die zarten jungen Blätter werden manchmal gegessen und auch als Tee-Ersatz verwendet. Blüten – gekocht. In Teilen Chinas als Nahrungsmittel verwendet.

Medicinal: Traditional Applications (mainly in Japan/China) External Use: Root Bark: For joint pain (as a compress or paste). Antimicrobial properties (against skin infections). Flower Extract: Diluted form for skin cleansing (antibacterial). Internal Use (rare and strictly dosed!): Seeds: In minimal amounts as an emetic (now obsolete!). Caution: Contains Wistarin (toxic lectin) - leads to nausea, vomiting, diarrhea. Modern Research Active Ingredients: Flavonoids (in flowers): Antioxidant. Triterpenoids (in bark): Anti-inflammatory. Potential Applications: Study on Wisteria extracts against certain cancer cells (preclinical, not confirmed). Warnings All parts of the plant are toxic (especially seeds). Symptoms when ingested: Abdominal pain, vomiting, dizziness. No self-medication! Traditional applications require expertise.

Other uses: The bark is used for making ropes and sandals. The branches can be used as cables and for bridge construction, known for their durability. Ropes and sandals are made from the bark, and the wood is also processed. In the Japanese Iya Valley (Tokushima Prefecture), bridges were constructed using the plant's vines to cross rivers. The vines were intertwined once they reached a sufficient length, and wooden planks were added.

Site: What matters is not the soil but the structure. An old wisteria develops woody stems as thick as an arm with considerable crushing force; timber trellises, gutters, downpipes, cladding and awnings get deformed or torn off. Plan from the outset for a free-standing steel or concrete frame at least 40 centimetres clear of the wall. It does not belong on living trees, which it strangles. It needs sun to flower at all, and free-draining, not overly calcareous soil. Important for planning: seeds and bark are poisonous, and the conspicuous pods hang within reach into winter — do not train it over play areas, sandpits or small-animal runs. The flowers are strongly scented and pull in large numbers of bumblebees in May, which can be a nuisance directly above a seating area. Care: Wisteria lives on pruning, and on two cuts a year. In July or August the long, whip-like new shoots are shortened to about five or six leaves; in January or February the same shoots are cut back again to two or three buds. The flower racemes come from these short spurs — prune at random, or not at all, and you get an enormous mass of foliage and hardly any flower. Do not feed nitrogen, which likewise only drives leaf; potassium in spring helps flowering. On limy soils chlorosis appears as pale leaves with green veins, countered by an acid mulch. Young plants need even watering in the first years and a firmly trained leader; late frosts can cost buds already formed.

Cultivars are propagated vegetatively, and for a solid reason: seedlings go through a long juvenile phase and often do not flower for ten to twenty years, some never properly. Plants bought in should therefore be grafted or cutting-grown — these flower from their third to fifth year. Grafting is done in winter by whip grafting onto seedling rootstocks; when planting, the graft union must stay above soil level or the stock takes over. Semi-ripe cuttings in June or July root under cover with bottom heat, and spring layering is equally reliable and takes a year. Sowing is worthwhile only for rootstocks: soak the seed for 24 hours and it germinates in warmth within a few weeks.

Japanese wisteria is one of the richest nectar sources in the May garden. The racemes, 30 to 60 centimetres long, open from the base over a good fortnight and are worked mainly by bumblebees, strong enough to force the pea flowers open; honeybees use them as well. The dense, interwoven framework of an older plant gives blackbirds, warblers and robins a well-covered nest site and shelter from wind in winter, much like an old ivy wall. As an East Asian species, though, it has no caterpillar following in Central Europe — native moths and butterflies do not feed on it — and the poisonous seeds are of no use to birds. Through the rhizobia on its roots it does at least enrich the soil with nitrogen.

Special: Twines clockwise, W. sinensis anticlockwise - the surest identification feature; flowers after the leaves emerge (sinensis before), racemes 30-60cm, over 1m in 'Multijuga', opening from the base; seedlings flower only after 10-20years -> buy grafted plants only; stems thicken to arm width+enormous crushing force -> steel frame only; seeds+bark poisonous;

East Asia: Japan. Japanese wisteria is native to the main islands of Honshu, Shikoku and Kyushu and is absent north of Hokkaido. It has been cultivated in Japan for centuries, trained over wide pergolas that people walk beneath in May; individual plants are more than three hundred years old. It reached Europe in 1830 through Philipp Franz von Siebold and the United States a few years later. In Central Europe it stays a garden plant and does not escape. The southeastern United States are a different matter: there it has spread from gardens into woodland, overwhelms the canopy and is classed as invasive.

In Japan wisteria grows in moist valleys, along stream banks, in thickets and open woodland of the hills and mountains. It is a liana: from the ground it seeks support on shrubs and trees and climbs them into the canopy, where it flowers. Its home climate is warm and summer-moist with cold but snowy winters — hence its good hardiness to around minus 20 degrees combined with a need for a long, warm growing season. As a legume it lives in symbiosis with rhizobia and fixes atmospheric nitrogen, which explains its independence from rich soil. Waterlogging and strongly calcareous ground, by contrast, suit it badly.