The genus wisteria has one species in North America, Wisteria frutescens, the first to be introduced to the UK, commonly called the Carolina Kidney Bean as it seeds resemble Kidney Beans. Has not become really popular as it requires hot summers to perform well. It differs from the Asian species in producing flowers on the current seasons growth making it a late June-July flowering plant. Best grown on a south facing wall and trained as an espalier.

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Wisterias as gardeners know them hail from Asia, the first one to be introduced was W. sinensis in 1816 and is to be seen adorning house walls throughout the country, with it's lilac-blue flowers and wonderful scent it is rightly the most popular wisteria. Many different forms of W. floribunda (Noda-fuji in Japanese) have been introduced from Japan, with longer racemes than W. sinensis and in differing colours, white, pink, mauve, blue and purple, ideally grown on pergolas or arches. Another species from Japan which is gaining in poularity is W. brachybotrys (Jama-fuji in Japanese, commonly called the Silky wisteria here due to the soft hairs on the young foloiage). Has broader racemes and larger individual flowers than W. floribunda in similar colours and having good scent.

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They belong to the family Fabeaceae (Pea Family) the flowers are borne on a raceme of varying length depending on species/cultivar, opening in succession from base to tip. Each individual flower consists of a standard, two wings and keels, like sweet peas. The standard has a small pale yellow patch at the base which is a guide to bees, who see it in ultra violet. They climb by twining round whatever is available to them and need careful handling by the gardener.

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CULTIVATION

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They are adaptable to virtually all soil types but do not like being waterlogged. When planting it is best to mulch with organic matter rather than incorporate in the planting hole. Water during dry periods for the first couple of years to aid establishment after which they cope very well in dry conditions. They climb by twining and are vigorous so careful pruning is required whatever support system is used. On walls vertical and horizontal wires need to be fixed using vine eyes along which the shoots are trained. Allow one shoot to go up the wire, tying in with plastic tubing and not allowing it to twine, pinch the tip when horizontal wires are reached and train out shoots either side.

In subsequent years prune back all side shoots to form flowering spurs. Wisterias will not flower with abandon until they have nowhere left to climb.

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They can be trained on pergolas and arches, which is very good for the longer racemed Wisteria floribunda cultivars. The pergola/arch needs to be tall enough to allow the racemes to hang down and yet allow pedestrian access without having to bend down, three metres is probably minimum height. Another good way of growing them is to plant to a strong 2.3 metre post banged in so that 1.8 metres is above ground. In this way growth soon reaches the top and with nowhere left to go enter flowering quicker than any other method of training. Can be used as a lawn specimen or part of a mixed border. Pruning can be carried out without the aid of ladders making maintainence easier. Beautifully trained specimens on large walls and pergolas are a wonderful sight however as long as one is prepared for the extra work involved.

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The most important aspect of pruning which can be daunting to some is summer pruning, all whippy shoots arising from the framework of the plant should be kept cut back so they do not become a nuisance, at least a couple of times during the growing season. This can be done with shears to speed up the work as after leaf fall the shoots can then be cut back to 2-3 buds when they are easily visible.  Older plants can build up too many spurs so occaisonal thinning of spurs needs to be carried with the winter prune.

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The flowers can be subject to late spring frost damage some years and in rural areas wood pigeons will peck at flowers and young foliage. Having said that a warm spring day with a plant in full flower, the air heavy with scent and the buzzing of bees is a gardening experience difficult to better.