Overview: Wisteria is a genus of about 10 species of twining, woody, deciduous climbers found in moist woodland and on streambanks 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 upto 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.

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 in my experience. My personal opinion is that Wisteria bonsai should be pruned to encourage flowering as you would any garden Wisteria. It is a very long-established gardening technique to prune back all shoots (that are not needed to form the structure of the tree) to within 5 or 6 inches of the main trunk or branch; leave 4-6 leaves on each shoot. This should be carried out after flowering and can be repeated as necessary 2 or 3 times until Autumn. In mid-Winter (December/January) reduce these spurs again to 3-4 inches, leaving only 2 or 3 buds.

These repeated prunings followed by a hard pruning in mid-Winter not only control the vigour of Wisteria but encourages flower production at the expense of leaf production. This repeated pruning also encourages dense, compact foliage and flowering. The second technique that must be applied to encourage prolific flowering in Wisteria is to repot at the correct time. Repotting in early -Spring, as is the norm with most Bonsai species, will interrupt and reduce flowering; repot immediately after flowering has finished when the tree can be allowed to put out vegetative growth.

Finally, feed correctly. As a member of the Leguminosae family, Wisteria are able to harness Nitrogen from the atmosphere. Feeding with fertilisers that have 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. Wisteria can (and do) suffer from rootrot if kept continually waterlogged or are planted in poor-draining compost.

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.

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.

Pots: Normally deep, glazed in a colour that compliments flowers.

Copyright © Written by Harry Harrington, of Bonsai4me.com.