I would like to grow wisteria vine. Please provide input on the different species, such as their bloom times, which ones smell the best, etc. Is the American species less aggressive than the Chinese? If so, how aggressive is it? Will I be pruning weekly?
There are two exotic species: Chinese wisteria (Wisteria sinensis) and Japanese wisteria (Wisteria floribunda). American wisteria (Wisteria frutescens) which is a native, is more successful in the southeastern United States than here in Michigan. Although it is cold tolerant to zone 5, you are more apt to find the Japanese here in the north since it will tolerate zone 4 temperatures.
Wisteria is a member of the pea family and climbs by twining its stems around whatever support is available. They’ve been known to consume fences, warp power poles, demolish trellises, and obscure people. All three can reach heights of 25 to 30 feet.
The Chinese is very showy, with flower clusters up to a foot long, which open before the foliage has expanded. The familiar blue-violet blooms appear in early to mid-May but are only faintly scented. There is a white form (W. sinensis ‘Alba’), which is very fragrant. Chinese wisteria may bloom within 3 to 4 years after planting.
Japanese wisteria is aggressive, producing perfect blue-violet blooms on old wood from mid-April to May. Again, depth of fragrance depends on the cultivar you select. Often, you will find the showier the blossom, the less fragrant it will be. ‘Macrobotrys’ (reddish violet), ‘Naga Noda’ (pale violet), and ‘Snow Showers’ (white) all offer significant fragrance.
If you have a sunny and moist site, the American wisteria will produce 6-inch long, pale lilac flowers in June to August on the current season’s growth. Blossoms appear after the foliage has developed. It is a handsome plant in both leaf and flower, showing greater restraint than the Asiatic bullies, according to Michael Dirr, a well-known woody plant book author. Because of the different bloom times, you may want to combine one of the Asian species with the American, although not necessarily in the same location, unless you have steel beams for support.
Whichever species you choose, select a named variety and plant in deep, moist, well-drained, and loamy soil with a soil pH of 6.0 to 7.0. A soil test will determine the pH and if amendments are necessary. The site must get 6 hours or more of sun. Prepare a 2- to 3-foot diameter space for the trunk and add peat moss, compost or aged manure to improve soil aeration and drainage. Wisteria can be trained as a single trunk tree or allowed to climb a structure. It must be supported by a strong pressure-treated wood arbor, pergola, or pole. Young plants should be fertilized annually until they fill the allotted space. Fertilizing encourages vegetative growth so don’t look for blooms. Once established, do not fertilize. Water only if foliage wilts. Both fertilizer and too much water produce green growth and limit flower production.
Certainly not weekly, but some pruning is required to maintain plant quality and promote flowering. Simply keep in mind to single out one strong leader from each main framework branch. Cut off the ends of all new side shoots just beyond the sixth or seventh compound leaf. Do this in summer. In winter, concentrate on pruning back the leader shoots by at least one-half. Cut side shoots to only one or two inches from their base.
It isn’t necessary to be a pruning guru to grow a wisteria of any make or model. Generally the famous frustration of lack of bloom comes from too much TLC—too much fertilizer, too much water and not enough drainage.