Your first encounter with wisteria (Wisteria spp.) at peak bloom may leave you feeling you've stumbled into a vintner's dream. Prolific grapelike clusters bathe the vine in scent and color. Hardy from U.S. Department of Agriculture plant hardiness zones 4 through 9, depending on the species, wisteria adds beauty and drama to its setting. With proper planning and a little effort, you can enjoy colorful, cascading clusters of your own.
Wisterias for Your Garden
Most gardeners turn to two main wisteria species for the clustered flowers they crave. Chinese wisteria (Wisteria sinensis) suits USDA zones 5 through 8. Each distinctive leaf holds seven to 13 leaflets. Feathery foliage waits to make its entrance until after the vine blooms. Japanese wisteria (Wisteria floribunda), which grows in USDA zones 4 through 9, bears 13 to 29 leaflets on leaves that unfurl alongside the blossoms. Less common than these species, but still beautiful, is the American wisteria (Wisteria frutescens). Hardy in USDA zones 6 through 9, this native vine saves its blossoms until foliage is fully in place. Wisteria vines grow vigorously, reaching 30 feet or more under normal garden conditions.
Flowers to Remember
Chinese wisteria heralds spring with abundant, aromatic blossoms. Clusters typically reach 12 inches long -- about the size of a bunch of grapes -- and flowers open all at once along bare branches. Violet-blue and white in most cases, the flowers may take on shades of pink. Racemes of Japanese wisteria blossoms soon follow, reaching up to 36 inches in length. They fill the air with heavy perfume. All shades of blue, lilac and lavender meld together in clusters that gradually open from the top, trailing down to the tip. American wisteria's profuse, lightly fragrant, summer clusters blend soft blue and lilac. Wisteria flowers produce beanlike ornamental seed pods. The pods, like other parts of wisteria, may be toxic if eaten.
Some wisterias demand extra care in exchange for blossoms. Grown from seed, the vines can take decades to flower. Cutting-grown vines generally yield blossoms in three years. For maximum blooms, give wisteria plenty of room in fertile, well-draining soil with six to eight hours of sun each day. American wisteria is the least tolerant of shade. Plant Chinese or Japanese wisteria where their early blooms get protection from spring frosts, or you may lose the flowers to cold. An established wisteria doesn't need fertilizer. Avoid high-nitrogen fertilizers in particular because they stimulate growth at the expense of blooms. Mature vines rarely require supplemental water. Slight dryness encourages wisteria flowers.
Pruning for Blooms
Control rampant wisteria, which is invasive in some areas, with diligent pruning. Pruning encourages grapelike blooms, too. Prune Chinese and Japanese wisteria twice each year: once in mid- to late-summer and again late in winter. Prune to control errant growth any time of year. Prune American wisteria right after it blooms and again in late winter, if you wish. Use sharp bypass pruners, and sterilize their blades with household disinfectant to avoid spreading disease. Wisteria flower buds form on spurs set in fall on Chinese and Japanese vines, but on new spring growth on American wisteria. Never cut off the woody spurs, or you'll sacrifice your blooms. The fat, fuzzy flowers buds are easy to spot.