Wisteria frutescens var. macrostachya Blue Moon

Wisteria 'Blue Moon' is a beautiful descendant of a wild American wisteria that is extremely cold-resistant. This variety charms with its long clusters of lavender-blue flowers that are dense and fragrant. They appear in abundance in late spring, along with its young leaves. The flowers bloom again, more sporadically, nestled in its beautiful dark green leaves. It flowers once or twice more during summer. Wisterias spontaneously and voluptuously wrap their long, twining stems around railings, fences, neighbouring plants, pergolas, and arbours, transforming them into flowering structures. 'Blue Moon' sometimes takes time to establish and bloom, but it is a beautiful garden plant that will make an even greater impact if trained as a tree.

The American wisteria is a woody, deciduous climbing plant belonging to the large Fabaceae family, just like clover, alfalfa, or lupins. Its subspecies macrostachya is native to humid forests and riverbanks in a geographic area ranging from southern Missouri and Illinois to eastern Kentucky. It has the peculiarity of producing its flower buds on the current year's wood rather than in summer, which protects the flowering from heavy frosts. Its long twining stems, slightly less vigorous than those of Chinese wisteria, lignify with age. It is a perfectly cold-resistant plant. It is undemanding in terms of soil (although it does not tolerate active limestone), and can grow in periodically waterlogged or, conversely, poor and fairly dry soils in summer if they are deep.

The compact and highly floriferous 'Blue Moon' was selected in Minnesota, USA for its resistance to long and harsh winters. Its stems easily reach 4m (13ft) in length and twine around supports spontaneously, in a counterclockwise direction. The growth of new shoots is rapid, with about 80cm (32in) in a single season if planted in moist soil. The main flowering of this variety takes place in May-June, on plants that are at least 3-4 years old. It develops on leafy branches located near the main lignified stems. It bears long clusters of small blue-mauve flowers speckled with yellow-green, measuring 20 to 35cm (8 to 14in). The tightly packed blooms emit a pleasant fragrance in calm weather. They open from the base towards the tip of the cluster. The plant reblooms during summer. Its flowering is nectar-rich and attractive to bees. The young bronze leaves appear at the end of flowering and then turn dark green, before turning yellow in autumn and falling off. They are 10 to 30cm (4 to 12in) long and divided into 9 to 15 rounded leaflets, giving the foliage a light appearance. The brown fruit is a flattened pod, 5 to 10cm (2 to 4in) long, which persists until winter. It contains numerous small brown kidney-shaped seeds. The 'Blue Moon' wisteria can live well over 50 years. 

'Blue Moon' is slightly less vigorous than its Asian counterparts, but is better suited for small gardens. It can enhance any facade or structure, no matter how modest. It is also particularly useful for covering a wall or an unsightly fence. It wraps itself around a fence or trellis without restraint if left to its own devices. It tends to smother surrounding plants. Plant it on its own in full sun (or partial shade in hot climates). Alternatively, plant it with equally powerful honeysuckles, such as the evergreen Lonicera x delavayi, with a fragrant yellow summer flowering, or the thornless Banksia rose 'Alba Plena', which is covered in small white pompoms in May. It also gets along very well with Clematis montana. With careful pruning, this variety can become a magnificent small tree, to be placed prominently in the garden.

However, be patient! Its first flowering only appears after 2 to 3 years, depending on growing conditions.