Wisteria macrostachya

Wisteria macrostachya, the Kentucky wisteria, is a highly attractive ornamental climber, valued for its less vigorous growth than Asian species and its repeat flowering in long clusters. This climber develops its foliage before the first clusters of flowers appear, towards the end of May. Reaching 25 cm in length, or even more, they consist of dozens of flowers ranging from mauve-blue to violet, depending on the plant. It flowers again in September, or sometimes even during the summer, increasing the ornamental appeal of this species. Nectar-rich, the flowers are, however, only lightly fragrant. Well suited to moist or even wet soils, whether ordinary or poor, it dislikes chalky conditions. Growing in full sun, it is highly resistant to frost and will enhance a pergola or arbour.

Wisterias are members of the large Fabaceae family, formerly known as Leguminosae. With nearly 800 genera, this botanical family includes food crops such as broad beans, peas and French beans, as well as wild or ornamental plants, shrubs such as brooms, trees (Gleditsia, Albizia...) and climbers, such as sweet pea, or Lathyrus latifolius. The genus Wisteria comprises only 7 to 9 recognised species, originating from North America and the Far East. The species macrostachya is now considered a subspecies of species frutescens (and is therefore named Wisteria frutescens subsp. macrostachya), brought back from Carolina (present-day United States) in 1724 by an English naturalist. W. Frutescens grows wild across a large area stretching from Texas to Florida and northwards to Kentucky, hence its common name. It is found in moist or distinctly wet areas, such as woodland edges or stream banks. Although wet, these sites are generally well drained. It is a twining plant that climbs by wrapping itself around its support in an anti-clockwise direction. It can then reach 10 m in length and flowers on young wood, bearing clusters 15 to 25 cm long.
The subspecies macrostachya has similar characteristics, with clusters that are slightly longer than those of the type species. Its growth is relatively moderate compared with other species, making it easier to grow in the garden and reducing the risk of it becoming invasive. Capable of reaching 10 m in good conditions, it more commonly reaches 5 to 8 m in height, with a spread of 3 to 4 m. Its attractive foliage consists of alternate, compound, odd-pinnate leaves, usually bearing 8 to 14 opposite lateral leaflets along a rachis and one terminal leaflet. The leaves are 15 to 30 cm long and 8 to 15 cm wide, giving the plant considerable presence and a distinctly exotic appearance. Deciduous, they emerge in spring before flowering, which does not begin until towards the end of May. Long clusters of 25 cm or more then extend towards the ground, adding clear architectural interest to this climber. They consist of dozens of papilionaceous flowers typical of the family, lightly fragrant, with a mainly bluish colour often shaded with mauve or violet. Nectar-rich, they attract bumblebees and honey bees, which should therefore be taken into account when choosing the planting site. The main flowering period in May-June is generally followed by a second flush in September. However, by regularly pruning off faded inflorescences, it is possible to enjoy several further flushes during the summer, significantly extending the flowering season of this wisteria.

Wisteria frutescens subsp. macrostachya is an outstanding species in more than one respect, and can be planted alongside other earlier-flowering species, such as Wisteria venusta 'Okayama', with mauve-purple flowers in April-May and even more moderate growth. Choose plants of comparable vigour to prevent one or the other from taking over. Passiflora coerulea is a good candidate, with its bluish passion flowers followed by highly decorative orange fruit. Trumpet vines are also capable of holding their own and will provide remarkable vivid colours. If there is no trellis or pergola, you can also train your wisteria up a tree, choosing a mature specimen with sufficiently strong branches. A spectacular effect is guaranteed!