Wisteria is a genus of about 10 species of twining, woody, deciduous climbers found in moist woodland and on stream banks in China, Korea, Japan, and central and southern USA where they will commonly reach heights of 10metres or more. They have alternate, pinnate, dark green leaves to 35cm long. The long leaves are suitable for bonsai styling as they are made up of a number of smaller leaflets that are around 5cm long.
Wisterias do not conform to normal bonsai styling; they are styled to show off their highly scented racemes of flowers up to 30cm long. Flower colour changes according to variety but is normally a mixture of blue, purple or white. Flowers appear in late Spring or Summer and are followed by pendant bean-like green seed-pods.
The two species of Wisteria normally seen as bonsai are W. floribunda/ Japanese Wisteria and W.sinensis (syn.W.chinensis)/ Chinese Wisteria. Both species are twining climbers; a common way to differentiate between the Japanese and Chinese Wisterias in the wild or in the garden is to study the way that the plant has twinned. The Chinese Wisteria will grow anti-clockwise whilst the Japanese Wisteria twines clock-wise.
The Japanese Wisteria pictured here can be found at Kew Gardens in London. It can be dated back to 1820 when it was propagated from the first Wisteria cuttings imported into the UK in 1816. Originally housed inside, this Wisteria was moved and planted outside since 1860.
ENCOURAGING WISTERIA TO FLOWER
Wisteria planted in the ground flower prolifically but as bonsai they can be more reluctant. Nearly every Bonsai Book ever written suggests a different approach to encouraging flower production. Firstly, it should be noted that what ever techniques are applied, Wisteria will not flower until they reach a certain age; this seems to be around 10 years.
Wisteria have two stages of growth; the first is the juvenile stage where they will produce vegetative growth (foliage and new extending shoots) and a mature stage where they will produce flowering spurs at the expense of vegetative growth.
In terms of bonsai, the trunk and branches of the Wisteria bonsai are developed first by allowing the roots plenty of room to extend; either by using a large pot or by annual rootpruning.
Once the trunk has developed, the tree is allowed to become completely rootbound. This stops all vegetative growth in the tree; that is, though it will produce new leaves each year, it will produce very few new shoots (if at all). The Wisteria stops producing juvenile vegetative growth and is forced into a ‘mature’ phase in its life where it tries to reproduce (make flowering spurs and flowers).
Finally, feed correctly. As a member of the Leguminosae family, Wisteria are able to harness Nitrogen from the atmosphere. Feeding with fertilisers that have anything other than a low nitrogen content will encourage excessive vegetative leaf-growth at the expense of flower production.
BONSAI CULTIVATION NOTES
POSITION: Full sun or partial shade. Wisteria bonsai can become quite top-heavy and care should be taken that specimens are not blown over in strong winds. Wisteria are fully-hardy when grown in the ground but due to the high moisture content of the roots, should be given some protection when temperatures drop below -5°C.
FEEDING: Feed with a low-nitrogen fertiliser fortnightly after flowering has finished until Autumn.
WATERING: Wisteria require large quantities of water in comparison to most other bonsai species and need heavy watering to keep them continually moist. In periods of hot weather during the Summer they will happily tolerate their pots being stood in a shallow tray of water to keep up moisture levels. However, water trays, if used, should be allowed to dry out daily.
REPOTTING: Repot every 2 or 3 years after flowering has finished in a basic soil mix. Wisteria can be repotted in early Spring as with other bonsai species but flower production will be affected.
Repot annually to encourage vegetative groth (at the expense of flowering)
PROPAGATION: Basal cuttings from side shoots in early to mid-Summer and root with bottom heat. Ground layer in Autumn or air-layer after flowering.
PESTS AND DISEASES: Leafspot, brown scale and aphids might be a problem.
STYLING: Wisteria are styled into forms that allow their flowers to cascade to their full length. Style trees to show off their flowers rather than their foliage. Use informal upright, slanting or cascade forms in medium to extra-large sizes.
