• Zones vary
• Full sun; W. Sinensis takes some shade
• Regular watering
• Climbs by: twining
Breathtaking in full bloom, wisteria is the queen of flowering vines. The sweet pea-shaped flowers grow in elongated clusters; violet blue is the most common color, though you'll see white and even pink wisterias as well. Leaves often reach 1 foot or longer, bearing seven to 15 or more leaflets arranged featherwise along a central leafstalk.
Most wisterias don't bloom right away. To shorten the flowerless period, buy the largest plant possible: a wisteria started from a 5-gallon container may bloom in 1 to 2 years, several years sooner than a 1-gallon plant.
Wisteria is easy to grow, but you will need to choose the planting location carefully. For Japanese wisteria, make sure vines will be in sun; they rarely bloom in shade. Chinese wisteria prefers sun, too, although it will flower even in some shade. Be sure to provide sturdy support.
These vines aren't fussy about soil, but they do need good drainage. In alkaline soils, they may suffer from chlorosis; treat the problem with iron chelates or iron sulfate.
Wisteria needs little to no fertilizer ― and in fact, feeding often curtails bloom. If a wisteria that you've been fertilizing fails to flower, stop the feeding; since buds for next spring's bloom are started early in the summer, you'll need to withhold fertilizer an entire growing season to see if excess fertilizer was responsible for the lack of flowers. If the vine again fails to bloom, try pruning roots in the spring (after you're sure no flowers are forthcoming): plunge a sharp spade vertically into the plant's root zone, cutting into the soil 1 foot away from the main trunk on all sides for each inch of the trunk's diameter. This treatment may shock the wisteria into blooming the following year.
Prune wisteria twice a year. During the summer months, numerous long streamers will emerge from all over the vine. Cut back most of these to side branches before they can tangle up in the main body of the vine; save those you want to use to extend the vine's height or length, and tie them to the underlying support. (You may need to repeat this chore 4 to 6 weeks later.) At the end of winter dormancy, check the vine again and remove additional tangling side streamers; also remove any dead or poorly placed stems.
Japanese wisteria (W. floribunda). Zones 2-24, 26, 28-41. Intensely fragrant blooms grow in clusters about 1 1/2 feet long. The typical color is violet to violet blue, but you'll find named cultivars in various other purple shades as well as in white or pink. Blossoms appear just as leaves emerge in spring. After the initial spring flush, vines continue to bloom off and on throughout summer, though flowering is less profuse than in spring. In autumn, leaves take on yellow to gold shades (even in mild-winter climates). The vine can reach 50 feet, but 30 feet is a more typical size.
'Texas Purple' starts flowering sooner than many other Japanese wisterias ― usually the first season after planting.
Chinese wisteria (W. sinensis). Zones 3-24, 26, 28-35, 37, 39. Chinese wisteria's blossom clusters are somewhat shorter than those of Japanese wisteria (to about 1 foot) and not as fragrant, but its floral display is more striking ― it blooms before leaves emerge, with all flowers in a cluster opening at once. There's a second, less profuse bloom in fall. The usual flower color is violet blue. 'Alba' is a white form; 'Cooke's Special' has longer-than-average clusters of medium-violet blooms.
Chinese wisteria is smaller than Japanese wisteria, typically attaining about 20 feet. Though it excels as a vine, it is sometimes pruned and trained as a single-stemmed weeping shrub, providing a dramatic focal point in the landscape. In warmer zones, provide protection from hot afternoon sun.