Wisteria

These vigorous climbers provide a reliable springtime show, says Miranda Kimberley.

Wisteria Frutescens - image: Flickr/Ezra Freelove
Wisteria Frutescens - image: Flickr/Ezra Freelove

Wisteria (or Wistaria) is one of the most-used climbers by gardeners and designers, but is none the worse for that. In spring or early summer its twining stems burst into bloom, giving off a heady fragrance. Certain varieties are being used to create half-standards, to serve as specimen plants for the patio or conservatory.

Wisteria are deciduous vines native to the eastern states of North America, China and Japan. There are 10 species and they all have pendent racemes of usually fragrant pea flowers, occasionally followed by green seed pods. The flower colour ranges from the pure white of Wisteria brachybotrys to lilac, mauve, pink and even dark purple, seen on W. floribunda 'Yae-kokuryu'.

The most commonly used species is the Chinese wisteria, W. sinensis Award of Garden Merit (AGM). It is a very vigorous climber that can extend for metres when grown up against a house. It produces deep lilac flowers in late spring that come before the leaves and hang down in columns. This species also repeat flowers in late summer, though the display is less spectacular.

W. floribunda, the Japanese wisteria, and its many cultivars are also very popular. The species has lilac flowers that open in early summer. It tends to have longer racemes than W. sinensis AGM so can look particularly striking when grown over an arbour or pergola. The flowers do not hang as well on walls and can get hidden by foliage.

Other species that are also used in the UK include W. brachybotrys, a shrubby type known as the silky wisteria because of its downy leaves, W. macrostachya and W. frutescens. All of these are fully hardy but still do best planted against a wall, ideally facing south or south-west. Wisteria like protection from early morning sun in frosty periods and shelter from cold winds. They should be grown in deep, quite fertile, well-drained but moisture-retentive soil.

Wisteria can be left to scramble through trees, to form fans or espaliers, as standard trees or over a wire framework. Formative pruning will be necessary for these growth forms and then twice-yearly thereafter. All shoots should be cut back to five to six buds around two months after flowering to divert energy from the long whips and into the remaining buds. The shoots should then be cut back again in late winter to two to three buds, aiming to form short flowering spurs.

Seed-grown Wisteria varieties take a long time to produce flowers - up to 20 years in some cases. For this reason, most commercially available specimens are grafted and will flower after as little as three years.

What the Specialists Say

- John Winterson, deputy buyer, RHS Plant Centres

"We sell a range of 27 Wisteria species and varieties, all of them grafted to give you earlier flowering in three-litre pots. The best seller is still the Chinese wisteria, W. sinensis AGM, followed by W. floribunda 'Multijuga' AGM, W. 'Lavender Lace' and W. floribunda 'Yae-kokuryu'.

"Among the larger flowering specimens the best seller is W. floribunda 'Issai' - this one is a good purple that flowers reliably. Our customers tend to prefer the stronger flower colours and whites rather than the pale colours or the pink ones and of course they want good scent. Other forms available include standards, which are very popular albeit rather pricey due to the time spent producing them.

"My personal favourite is W. floribunda 'Alba' AGM, with its stately-looking pure white flowers that can be up to 60cm long and are sweetly scented too, so ideal for near the door.

"Wisteria are rapid growers so pruning them twice a year is a must if you want to keep your plant in check and flowering regularly. Plants can take a while to get established and trained but it's well worth the effort."

- Nick Hourhan, owner, Spring Reach Nursery, Surrey

"There are lots of different varieties of Wisteria but I sometimes struggle to see the colour differences. "W. sinensis is still the tried and tested winner. It has a lovely fragrance and repeat flowers in late summer, although W. sinensis 'Alba' AGM doesn't repeat flower so much as the type.

"W. floribunda 'Rosea' AGM has rose-pink flower racemes up to a foot long that produce one of the best fragrances. For longer flowers you can use W. floribunda 'Multijuga' AGM, which has panicles over two feet (60cm) long. It takes a long time to flower well though, even when grafted.

"The key selling point of Wisteria is the plant's flowering ability and fragrance. As a quick-growing, rampant climber, Wisteria is hard to beat. Customers sometimes ask for a compact type but they should be aware they all can reach 60 feet (18m), though there are one or two that are excellent grown as half standards.

"You can be inventive with Wisteria, training it through a tree or onto a wire frame, which can create a living parasol in the late spring. Later in the summer it will be a green canopy of leaves."

In Practice

- Dan Bowyer, director, Fisher Tomlin

"Wisteria, along with jasmine and Clematis, is one of the climbers that just keep being used again and again. They are fantastic over a pergola, as well as up a house wall. They produce incredible blooms with a lovely fragrance, providing a romantic element to designs. In a large country garden they also suit being used on walkways or arbours.

"If I am underplanting a Wisteria I tend to use plants that provide good evergreen structure because they will add interest when the climber is not in flower or leaf. I use W. sinensis and W. sinensis 'Alba' AGM a lot. I think the climate in the past few years has affected the flowering ability of Wisteria, but in a good sunny spot they should romp away. However, basal stems can root along the ground and spread quite a long way."

Species and cultivars

- W. brachybotrys, the silky wisteria, has a shrubby habit, downy, dark green foliage and large, highly fragrant white flowers on short racemes.

- W. brachybotrys 'Shiro-kapitan' (syn. W. venusta 'Alba') has short, rounded blooms of pure white, set against pale green leaves. Has a long flowering period and is one of the quickest to flower after planting.

- W. 'Caroline' has dense racemes of strongly scented mauve/violet flowers, fading to white, that appear before the leaves.

- W. floribunda, the Japanese wisteria, produces long racemes of scented lilac blue flowers in early summer followed by velvety seed pods. Stems grow up to 8m long.

- W. floribunda 'Alba' AGM has long pointed trusses of white flowers tinted lilac on the keel.

- W. floribunda 'Domino' has medium-length trusses of mauve-blue flowers, appearing from a young age.

- W. floribunda 'Harlequin' has contrasting darkish purple and pale mauve flowers. The leaf midribs and stems are also darkly coloured.

- W. floribunda 'Kuchi-beni' is also known as 'Peaches and Cream' for its very pale pink flowers tipped with purple, in racemes up to 45cm long.

- W. floribunda 'Multijuga' (syn. W. 'Macrobotrys') AGM has exceptionally long flowering racemes (up to a metre) of pale mauve flowers that have a delicious fragrance.

- W. floribunda 'Rosea' AGM is an early summer flowering variety with long strands of fragrant, pink flowers with yellow markings. Can also be grown as a standard.

- W. floribunda 'Yae-kokuryu' (syn. 'Black Dragon') also has long racemes of double flowers that are dark purple in bud, resembling bunches of grapes, opening to lavender blue with purple centres.

- W. x formosa is the result of crossing W. floribunda and W. sinensis. Has racemes of up to 25cm, with all the pale violet flowers blooming at once in early summer, unlike W. floribunda, whose blooms open gradually from the base of the raceme.

- W. frutescens is a hardy North American species, growing up to 10-12m. Produces short racemes of gently fragrant pale purple-lilac flowers from June to August. Less vigorous than other species, it can be grown as a standard.

- W. frutescens 'Amethyst Falls' PBR bears compact clusters of blue flowers from a young age in spring and again in summer. Less vigorous than most wisterias, it grows no more than 3m high.

- W. 'Showa-beni' is the most pink Wisteria, deeper in colour than W. floribunda 'Rosea', with shorter, more rounded flowers.

- W. sinensis AGM, the Chinese wisteria, is much more vigorous than W. floribunda, growing up to 30m in height. It produces hanging racemes of lightly fragrant, lilac flowers in spring that precede the leaves. Repeat flowers in summer and has velvety seed pods in autumn.

- W. sinensis 'Alba' AGM is a white form, producing mid-length racemes, and less vigorous than other sinensis varieties.

- W. sinensis 'Prolific' produces abundant, highly scented blue-violet flowers in spring. It has larger flowers than the type and can start blooming in the first or second year after planting.


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