Japanese wisteria

Japanese wisteria: how do you recognise it?

Habit

Vigorous, woody twining climber up to 8–10 m, with thick, twisting stems; can also be grown as a free-standing standard.

Leaf

Alternate, odd-pinnate with 13–19 leaflets, 20–35 cm long.

Stems

Grey, woody stems that twist around their support.

Flower

Hanging racemes of 30–50 cm, violet, pink or white and fragrant, May–June, at the same time as the leaves; they open from top to bottom.

Fruit

Velvety pods of 10–15 cm; the seeds are poisonous.

Difference from Chinese wisteria

Chinese wisteria has fewer leaflets (7–13) and shorter racemes whose flowers open almost all at once, before or with the leaves.

Flowering: May–June · Pruning: January–February and July–August

Identify by feature: Purple or blue flowers · Hanging flower clusters · Pods · Twining climbers

Looks like it, but isn’t

• Chinese wisteria Wisteria sinensis: fewer leaflets (7–13) and shorter racemes whose flowers open almost all at once, before or with the leaves. Difference from Chinese wisteria

Why grow it?

• Racemes of 30–50 cm, up to a metre in ‘Macrobotrys’: longer than those of Chinese wisteria.
• The racemes open gradually, so flowering lasts a long time.
• Fragrant flowers in May–June, busy with bumblebees and bees.
• Gives shade over a pergola or patio in summer.
• Can live to a great age and develops an impressive, gnarled trunk.

Japanese wisteria: where does it grow best?

• Full sun: in shade it hardly flowers.
• Any well-drained soil that is not too wet.
• It twines around its support and needs a very sturdy pergola, heavy wires or a wall trellis on spacers; light structures give way after a few years. The long racemes hang best from a pergola.
• Keep it away from downpipes, gutters, shutters and trees: the stems grow so strong they can strangle or twist them.

Light

Full sun

Legal basis

Any garden soil

Moisture

Normal

Size

10 m tall, 5 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Common laburnum: Flowers in May–June with yellow racemes: together, over a pergola or arch, a tunnel of yellow and violet racemes.
• Californian lilac: An evergreen shrub with blue flowers in spring, for the same sunny wall.
• Common sage: A grey, evergreen small shrub for the dry, sunny foot of the pergola, with violet flowers in June.

Good and bad companions

Best kept away from

• Twines around young trees and shrubs and can strangle them: hawthorn, goat willow, japanese cherry, judas tree, chusan palm, olive tree

Japanese wisteria: when and how to plant it?

1. Plant in autumn or spring, from a pot.
2. Buy a grafted plant or one grown from a cutting that is already flowering: a plant grown from seed may take ten years or more to flower.
3. Plant 30–50 cm from the wall or post and guide the shoots to the support.
4. From the start, choose one or a few main stems and tie the side branches in horizontally: that is where the racemes will come later.

Care

Watering

In dry spells during the first year, and in late summer, when it forms next year’s flower buds.

Feeding

Little: too much nitrogen gives lots of leaves and few flowers.

Tying in

Tie young stems in loosely and check every year that they are not growing into the wires or ties.

Runners

Long shoots creeping over the ground can root: cut them off in good time.

Tip: Let the racemes hang freely: they look their best from a horizontal pergola, whereas against a wall they are half hidden among the young leaves.

Japanese wisteria: when to prune it?

Pruning months: January–February and July–August.

When: Twice a year: in July–August and in January–February.

How:

• In summer, cut the long new shoots back to 5–6 leaves; in winter, shorten them further to 2–3 buds. This makes it form flower buds instead of long stems.
• In summer, also remove shoots growing towards gutters, windows or the roof.
• In winter, spare the fat, round buds: these are the flower buds; the narrow, pointed ones are leaf buds.

Caution: A plant grown from seed may take ten years or more to flower: buy a grafted plant instead.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Layering

In spring, lay a long, flexible shoot on the ground and cover a section with soil; after a year you can cut it free.

Sowing

Possible, but a plant grown from seed may take ten years or more to flower, often less well: buy a grafted plant instead.

Japanese wisteria: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Hardy; the flower buds can be damaged by night frost in April–May, though.
• In winter you can see its shape best: the ideal moment to check the structure and tie in stems.

Diseases and pests

• No flowers: Usually a seedling, too much shade, too much fertiliser or too little pruning. Prune twice a year and give no nitrogen.
• Bud drop: The flower buds fall before opening, because of drought or night frost in spring. Water in dry spells.
• Strangling: Stems in downpipes, gutters or around young trees. Cut them away in good time; a thick stem can no longer be removed without damage.

Through the year

• January: Winter pruning: shorten side shoots to 2–3 buds.
• February: Finish winter pruning; check the structure and wires.
• April: Buds swell: watch out for night frost.
• May: Flowering begins, together with the leaves: the racemes open from top to bottom.
• June: Last flowers; remove spent racemes and pods.
• July: Summer pruning: cut long shoots back to 5–6 leaves.
• August: Summer pruning; water in dry spells.
• October: Planting.

What can you use it for?

Garden and landscape

Spectacular flowering climber for a sturdy pergola or house wall; the long racemes look best hanging from a pergola.

For wildlife

Bumblebees and bees flock to the flowers.

Caution: Seeds and pods are poisonous. The stems grow so strong they can strangle gutters, downpipes and young trees.

Did you know?

• It twines around its support in the opposite direction to Chinese wisteria. In the cultivar ‘Macrobotrys’ the racemes reach a metre in length.
• In Japan it is called ‘fuji’; there are wisterias more than a hundred years old there whose pergolas cover entire gardens.
• The species name ‘floribunda’ means ‘flowering abundantly’.