Answer: Wisteria should be pruned at the end of the dormant season, prior to the onset of spring growth. Late February would be a good time for your area.
Wisteria is a spring blooming vine. Therefore when you prune in winter you are removing potential bloom buds. Some gardeners like to do some light pruning through the growing season to shape the vine. This minimizes the need for dormant season pruning.
How you prune is up to you. Some gardeners want wisteria to grow an upright trunk that spreads into an "umbrella" shaped top. Others train it down a fence and trim the side shoots back to short (about 1 foot) spurs, much like some grapes are pruned.
Hope this helps. Good luck with your wisteria!
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