Wisteria floribunda Macrobotrys De Belder

Wisteria floribunda Macrobotrys De Belder is a rare Japanese wisteria, which can be admired in Belgium at the magnificent Kalmthout Arboretum, which was taken over in 1952 by Georges, Robert, and Jelena De Belder. On the mother plant of this wisteria, sumptuous draperies of clusters of flowers in two shades of violet, sometimes reaching a length of 1.4m (5ft), bloom with a slight honey fragrance. Like all Japanese wisterias, 'De Belder' is an extremely vigorous climbing plant that requires space and a very sturdy support. The floribunda species is characterised by its twining stems that wrap clockwise around their support, unlike those of its Chinese cousin.

The Japanese wisteria, known as Wisteria floribunda in Latin, is a large and fast-growing climbing plant belonging to the Fabaceae family, just like clover, alfalfa, and lupins. It is native to Japanese forests and was introduced to Europe in the mid-19th century. Its long twining stems, which can reach a length of 10m (33ft), lignify with age. Sometimes a bit slow to establish, it is a robust plant, perfectly resistant to cold, not very demanding in terms of soil (although it does dislike excessive limestone), and capable of growing in poor and dry soils in summer if they are deep. Its roots are deep and trailing.

The 'De Belder' variety stands out for the length of its inflorescences and its more colourful flowers. Its stems, which can easily reach 8 to 9m in length, spontaneously twine around supports. The growth of new shoots is very rapid, covering several metres in a season in moist soil. Flowering occurs after that of Chinese wisterias, in May-June, on young grafted plants. It develops on already foliated branches located not far from the lignified main stems. It takes the form of pendulous clusters of butterfly-like flowers, 60cm (24in) to over 1m (3ft) long, each counting hundreds of flowers, less fragrant than those of the Chinese wisteria, but more numerous and remarkably arranged. Each flower, pale mauve in colour, is enhanced by wings and a more violet keel, as well as a small yellow-green spot. They open successively, from the base to the tip of the cluster. After the flowers, pendulous, flat, and green pods appear, swollen at the seed level, becoming brown when ripe. The young bronze-coloured leaves appear before flowering and then turn a light green colour. They are 20 to 30cm (8 to 12in) long and divided into 13 to 19 ovate leaflets, giving the foliage a light appearance. Before falling in autumn, the leaves take on a beautiful golden colour. Very long-lasting, the Macrobotrys Wisteria can live well over 50 years. Its flowers are rich in nectar. All parts of the plant are toxic to humans.

In spring, wisterias transform grids, fences, facades, arbours, and pergolas. They deserve to be planted for their extraordinary beauty, their impressive vigour, their very accommodating nature, and their excellent resistance to the coldest temperatures. The De Belder Japanese wisteria is a variety that is as spectacular as it is easy to grow. This lively plant is particularly useful for covering a wall, facade, or unsightly fence. It will twine around a trellis or lattice without restraint if allowed and may tend to smother surrounding plants. It prefers a solitary location, in full sun or partial shade in a warm climate. Alternatively, associate it with other vines as powerful as it, such as Lonicera x delavayi, evergreen, with its fragrant yellow summer flowers, or Banks' Rose 'Alba Plena', thornless and covered with small white pompons in May. The floribunda wisteria also gets along very well with Clematis montana and trumpet creepers, which take over in summer.

However, be patient: the first flowering of the Wisteria may not appear until 2 to 3 years, or even longer, depending on the growing conditions.