Chapter 135 Wisteria species

135.1 Wisterias

A Japanese wisteria in full summer foliage. While still impressive in summer, this specimen comes into its own in spring when the foot-long panicles of purple flowers are present. Link to original image.

Three species of Wisteria are commonly grown.

Species name	Common name	Native Region	Notes
Wisteria floribunda	Japanese wisteria	Japan, Korea	Largest, most spectacular blooming of the 3 species
Wisteria sinensis	Chinese wisteria	Eastern China	The most aggressive and invasive species; also most susceptible to frost of the 3 species
Wisteria frutescens	American wisteria	Virginia to Texas, Florida, Iowa	Smallest flower racemes; much less invasive

135.1.1 Soil: General Deciduous / Rich Conifer Mix

Ratio: 3 parts bark, 1 part grit

Add-ins: dolomitic limestone (~5 lbs/yd), Tree-Tone (15 lbs/yd)

pH: ~6.5 (slightly below neutral)

Moisture: Average

135.1.2 Light

Routine: full sun is needed for strongest flowering.

Summer: Mid-day shade only if showing signs of heat stress.

135.1.3 Cultivation Notes

A free-standing wisteria at Longwood Gardens. Wisterias grow larger and more rapidly when provided with supports on which to climb. Link to original image.

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 root pruning.

135.1.3.1 Potting & Root Pruning

Schedule: repot in spring.

Notes: be careful if you are root pruning wisteria vines in the ground in fall. This is standard preparation for lifting and potting up in spring, but it also can stimulate flowering and increase the risk of transplant shock. When root pruning in the ground, be sure to remove any flower buds; they only drain energy from the vine that should go into recovering from being transplanted.

In general, wisterias dislike being transplanted, so keep root manipulation to a minimum.

135.1.3.2 Top & Branch Management

Wisterias need regular pruning in order to control size and shape of the plant and to encourage flowering. They also only bloom on new wood, so pruning aims to maximize the new wood.

Heavy pruning: wisteria re-sprouts vigorously if cut back severely, but this should be avoided if possible, because new shoots may take years before they flower. It also resents repeated heavy pruning of older wood. Branches may die back after heavy pruning, so minimize the number of large cuts. Make large pruning cuts in winter.

Fine pruning: prune wisteria in late winter. Remove at least half of the prior year’s growth, leaving just a few buds per stem. After flowering, cut shoots to 2-3 leaves. Repeat 2-3x before fall.

Leaf pruning: does not like to be defoliated.

135.1.3.3 Feeding

Avoid high-nitrogen fertilizer. Wisterias are legumes, so fix their own nitrogen. Too much nitrogen will cause excessive foliage growth and poor flowering. A good choice would be a lower-N organic fertilizer like Espoma Tomato Tone (3-4-6) or Flower-Tone (3-4-5).

Additional phosphorus from superphosphate, rock phosphate, or bone meal at the start of the growing season can improve flowering.

135.1.4 Pests & Problems

Although susceptible to a number of foliage-chewing insects and fungal diseases, none are significant.

Failure of vines to produce flowers may be attributable to a number of causes including death of flower buds in winter, too much shade, plants too young (especially seed grown ones), improper pruning or overfertilization.

135.1.5 Winter Storage

Store outdoors. Mulch thoroughly to protect from sudden cold spells. Try to place in a shaded area so buds do not break in a mid-winter warm spell.

135.1.6 Propagation Notes

A white-flowered cultivar of wisteria. Link to original image.

Named cultivars are available at garden centers. Starter vines can be found growing wild; most landowners are happy to be rid of them. In my experience, the seeds do not always germinate reliably.

135.1.7 Artistic & Styling Notes

Wisterias do not conform to normal bonsai styling; they are styled to show off the long racemes of flowers in spring.

Wisteria planted in the ground flower prolifically but not until they reach maturity, at around 10 years old. As bonsai they can be more reluctant to flower, and can skip years.

135.1.8 Additional Information

135.1.8.1 Natural History

Wisterias are twining, woody, deciduous climbing vines found in moist woodland and on stream banks. Old vines may reach 40 feet high and have basal calipers of several inches. They have alternate, pinnate, dark green leaves up to 14 inches long. These are not a problem for bonsai because the leaflets are much smaller.

Flowers are a mix of blue, purple, and white. They appear in late spring in our area.

The two Asian species are used most often in bonsai. The way to differentiate between the Japanese and Chinese wisterias is to look at how the vines twist around each other; Chinese wisteria vines twist counter-clockwise while Japanese wisteria twists clockwise. American wisteria is uncommon. It twists counter-clockwise, but has smaller vines overall with shorter flowering bunches (6 inches or less) that are weakly fragrant if at all. American wisteria also flowers after leaf buds break; the Asian species bloom before the leaves appear.

135.1.8.2 In Cultivation

All wisterias need a sturdy support structure on which to grow. Without support they do not grow nearly as rapidly.