Wisterias belong to the Pea family, Leguminosae, and are most valued for their pendulous racemes of beautiful blue, purple, rose, mauve or white flowers in late spring and early summer, which are followed by long, flat seedpods. They usually bloom again later in the year. Their compound pinnate leaves are also very pretty. These plants are great for growing on walls, pergolas, and trellises. They can even be trained into bushes and small standards. There are primarily two types of Wisterias – those that twine from left to right and those that twin from right to left. W. floribunda (Japanese Wisteria) can climb up to 30 feet high and have leaves consisting of 13-19 leaflets. The fragrant flowers appear as the leaves unfurl and are produced in racemes up to 18 inches long. The bluish-purple or violet blue flowers open from the base of the raceme upward. The stems of this variety twine in a clockwise direction. W. floribunda from macrobotrys Multijuga has 1 to 3 foot long racemes of aromatic, lilac flowers shaded with bluish-purple. It is wise to grow this form on a pergola or arch to allow room for the long flower clusters. W. sinensis (Chinese Wisteria) can grow from 60 to 100 feet high with suitable support. The leaves consist of 9 to 13 elliptic to elliptic-oblong leaflets. In late spring, before the foliage appears, 8 to 12 inch long racemes are produced. The pretty, 1 inch long, mauve or deep lilac flowers open all at once and are followed by velvety seedpods. This variety usually produces another small batch of flowers in late summer. W. venusta (Silky Wisteria) is a vigorous growing plant that can reach a height of up to 30 feet. The leaves consist of 9 to 13, oval, velvety leaflets. In late spring and early summer, 4-6 inch long reacmes of large, white flowers are produced. They are also followed by velvety seedpods. (*It should be noted that Wisterias are poisonous if eaten*).
Grow Wisterias in good, fertile, loamy soil that has excellent drainage. Choose a location that receives full sun. Large, quick-growing varieties may need a yearly hard pruning in late winter to keep them within bounds. This can be followed in late summer by a second trimming, which consists of shortening the leafy shoots to five or six buds. However, when you first plant your Wisterias, focus on forming a strong framework of primary branches.
Wisteria is one of the most beautiful of the flowering vines. One often asked question is “How do I get my wisteria to flower?” First, they generally do not flower when young (4-5 years old). Secondly, they do need full sun. So grow them over an arbor or large trellis. They seem to need the sun to produce flower buds. Thirdly, if they are watered and fertilized too much, they will devote all energy to growing, but not get any flowers.
Wisteria is a very aggressive grower. Fertilizing and pruning need to be done appropriately. Any fertilizing should only be done in youth, or to add only phosphorous to help encouraging blooming.
Pruning of wisteria is usually done a few times over spring and summer. Any major pruning or reshaping should be done just after they flower (or should have). The 2-3 cuts throughout the summer, cut back long, new shoots or 2 or 3 sets of leaves, not all the way back. They are then neatened up for the fall color display of yellow-gold. Also, root pruning of the vines can sometimes encourage flowering. To do this, insert a shovel into the ground approximately 12-18” from the trunk at several different places (but do not make a circle).
One other point worth mentioning is that wisteria sinensis tend to bloom easier without judicial pruning.