Twining, woody vines of great size, long life, and exceptional beauty in flower. So adaptable they can be grown as trees, shrubs, or vines. All have large, bright green leaves divided into many leaflets; spectacular clusters of blue, violet, pinkish, or white blossoms and velvety, pealike pods to about 6 in. long. Fall color in subdued shades of yellow. To get off to a good start, buy a cutting-grown, budded, or grafted wisteria; unnamed seedlings may not bloom for many years. If you start with budded or grafted plants, keep suckers removed for the first few years, or they may take over. Do not allow aggressive Asian species to grow on trees or escape into ornamental areas, as they will quickly smother the landscape. Also be wary of growing them near the house, as their muscular stems can tear apart structures. Wisterias resist damage by browsing deer.
W. brachybotrys. SILKY WISTERIA. Native to Japan. Silky-haired, 8- to 14-in.-long leaves divided into 9 to 13 leaflets. White, very large, long-stalked, highly fragrant flowers in short (4- to 6-in.) clusters that open all at once during leaf-out. Older plants (especially in tree form) have remarkably profuse bloom. 'Shiro Kapitan' ('Alba') is the most commonly sold form; it bears pure white (sometimes double) flowers with yellow markings. 'Murasaki Kapitan' ('Violacea'), bears blue-violet flowers with white markings. 'Okayama' has faintly scented deep mauve blossoms.
W. floribunda. JAPANESE WISTERIA. From Japan. Leaves are 1216 in. long, divided into 15 to 19 leaflets. Very fragrant, 112-ft. clusters of violet or violet-blue flowers appear during leaf-out. Clusters open gradually, starting from the base; this prolongs bloom season but makes for a less spectacular burst of color than that provided by W. sinensis. Many selections are sold in white; pink; and shades of blue, purple, and lavender, usually marked with yellow and white. 'Macrobotrys' ('Longissima', 'Multijuga') has long (112- to 4-ft.) clusters of violet flowers. 'Longissima Alba' bears 2-ft. clusters of white blossoms; 'Ivory Tower' is similar. 'Rosea' has lavender-pink blooms; 'Violacea Plena' sports very full clusters of double, deep violet-blue flowers. 'Texas Purple' blooms at an early age.
W. frutescens. AMERICAN WISTERIA. Native from Virginia to Florida and Texas. Leaves 712 in. long, divided into 9 to 15 leaflets. Later blooming and less vigorous than W. floribunda and W. sinensis, with thinner stems; not destructive. Mildly fragrant, pale lilac flowers with yellow blotch appear in dense, 4- to 6-in.-long clusters in late spring after leaf-out; blossoms look like grape clusters. 'Amethyst Falls' has vivid lilac-blue flowers. White-flowered 'Nivea' blooms earlier than the species.
W. macrostachya. KENTUCKY WISTERIA. Native from Illinois to Texas. A good choice for smaller gardens. Like W. frutescens, blooms among new leaves in late spring, after the Asian species bloom. Mildly fragrant flowers are light blue to violet or blue-purple, in 8- to 12-in.-long, fragrant, pendulous clusters. Shiny leaves usually divided into nine leaflets, each to 3 in. long. The 4-in. pods are smooth, sometimes twisted. Less vigorous and better behaved than Asian species. Not destructive. 'Clara Mack' has white flowers. 'Bayou Two o' Clock' has blue-violet flowers held in long, pointed racemes. 'Pondside Blue' bears pale blue-violet blossoms.
W. sinensis. CHINESE WISTERIA. Native to China. Leaves are 1012 in. long, divided into 7 to 13 leaflets. Violet-blue, fragrant flowers appear before leaf-out; they come in shorter clusters (to 1 ft.) than those of W. floribunda but make quite a show by opening all at once, nearly all along the cluster. 'Alba' has white flowers. 'Cooke's Special' is a grafted form with blue-purple flowers to 20 in. long. Blue-violet 'Caroline', probably a hybrid, blooms early and is highly fragrant.
Plants are not fussy about soil but need good drainage; in alkaline soil, watch for chlorosis (yellow leaves with green veins) and treat with iron chelates or iron sulfate. Pruning and training are important for control of size and shape and for bloom production. Let newly planted wisteria grow to establish framework you desire, either single trunked or multitrunked. Remove stems that interfere with desired framework and pinch back side stems and long streamers. For single-trunked form, rub off buds that develop on trunk. For multiple trunks, select as many vigorous stems as you wish and let them develop; if plant has only one stem, pinch it back to encourage others to develop. The main stem will become a good-sized trunk, and the weight of a mature vine is considerable. Support structures should be sturdy and durable.
Tree wisterias can be bought already trained; or you can train your own. Remove all but one main stem and stake this one securely. Tie stem to stake at frequent intervals, using plastic tape to prevent girdling. When plant has reached height at which you wish head to form, pinch or prune out tip to force branching. Shorten branches to beef them up. Pinch back long streamers and rub off all buds that form below head.
In general, wisterias do not need fertilizer. Prune blooming plants every winter: Cut back or thin out side shoots from main or structural stems, and shorten back to two or three buds the flower-producing spurs that grow from these shoots. It's easy to recognize fat flower buds on these spurs.
In summer, cut back long streamers before they tangle up in main body of vine; save those you want to use to extend height or length of vine and tie them to supporteaves, wall, trellis, arbor. If old plants grow rampantly but fail to bloom, withhold all nitrogen fertilizers for an entire growing season (buds for the next season's bloom are started in early summer). If that fails to produce bloom the next year, you can try pruning roots in springafter you're sure no flowers will be producedby cutting vertically with a spade into plant's root zone.