Answer: There is always some confusion when it comes to pruning wisteria. The two species most commonly grown are Wisteria floribunda (Japanese wisteria) and Wisteria sinensis (Chinese wisteria), both of which bloom before or with the unfolding of the leaves.
Pruning wisteria extensively during the dormant season may encourage rampant vegetative growth the next spring. Instead, in July prune out the long, straggly growth except those branches needed for climbing. This is more likely than anything else to induce flowering. Shoots should be cut back one-third to one-half their length. This will induce them to produce the short spurs that will bear next season's flower clusters.
Wisterias are normally vines, but pruning can make them take shrubby and/or weeping forms, if that's what you wish. Heading back young shoots holds the height at a definite point and after several years, the plant produces a trunk-like stem. Then leaders can be allowed to droop to the ground.
Wisteria will bloom abundantly if planted in good garden loam with full sun, watered well the first growing season and pruned in the summer. Fertilizer isn't recommended. Feeding wisteria usually results in lots a vegetative growth at the expense of blooms.
It sounds as though your wisteria is overgrown. Now is the time to systematically cut it back, both to control its size and to encourage the development of flowering spurs for next season's flower display.
Best wishes with your wisteria!
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