Wisteria frutescens var. macrostachya Clara Mack

Wisteria 'Clara Mack' is a beautiful variety of American wisteria with pure white flowers. It is renowned for its unparalleled cold resistance and appreciated for its moderate growth. Its dense clusters of flowers exude a sweet grape scent that is particularly pleasant. This climber first blooms in June, among foliage that is darker and shinier than that of Chinese and Japanese wisterias. They are produced again, more sporadically, throughout summer. Like most American wisterias, this species blooms from a young age. 

American wisteria is a woody and deciduous climbing plant belonging to the large Fabaceae family, just like clover, alfalfa, and lupins. Its subspecies macrostachya, which is more northern, is native to moist forests and stream banks in a geographical area ranging from the south of Missouri and Illinois to the east of Kentucky. Its long voluble stems, slightly less vigorous than those of Chinese wisteria, are hairy when young and quickly lignify. It is undemanding in terms of soil (although it fears active limestone), and can grow in periodically waterlogged or, conversely, poor and fairly dry soils in summer, if they are deep. This species is considered more cold-resistant than Asian wisterias because it produces flower buds on the current year's wood rather than in summer, which protects the flowering from heavy frosts.

The stems of 'Clara Mack' can easily reach 5 to 6m (16 to 20ft) in length, and they naturally wrap around supports in a counterclockwise direction. The growth of new shoots is very rapid, reaching 1 to 2m (3 to 7ft) in a single season if planted in moist soil. The main flowering of this variety occurs in May-June, depending on the climate, on young plants. It is less abundant than that of Chinese and Japanese wisterias, and it develops among the leafy foliage. It produces long clusters measuring 25 to 30cm (10 to 12in), in which up to 50 small white papilionaceous flowers are tightly packed. They emit a pleasant fragrance in calm weather. They open from the base to the tip of the cluster. The plant easily re-blooms during summer. The young bronze leaves then turn a slightly shiny dark green colour, before turning yellow in autumn and falling. They are 10 to 30cm (4 to 12in) long and divided into 9 to 15 ovate leaflets, giving the foliage a light appearance. Its flowering is nectar-rich and attractive to bees. 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. It can live well over 50 years.

'Clara Mack' is the perfect choice for gardens in areas with long, cold winters. This grand romantic plant can enhance any facade or structure, no matter how modest. It is particularly useful for covering a wall or unsightly fence, wrapping around any sufficiently sturdy support. Plant it in a solitary position, in full sun or partial shade in warm climates. Alternatively, plant it with vigorous climbers such as Clematis montana, a trumpet creeper, or even an aristolochia. With patient and regular pruning, this climber can become a magnificent small tree that can be prominently placed in the garden.

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