On the bright side, wisteria in bloom is possibly the most beautiful vine you’ll ever see. On the dark side, if you don’t prune it twice a year (March and July), you can expect few if any blooms, and the vine’s rampant growth can take the roof off a house. If you own a wisteria, now is the time for its winter pruning.
These directions apply to a wisteria grown in full sun, with strong vigour and rambunctious growth. For a vine in lower light that’s not growing strongly, hard pruning may not be necessary every year. A hard winter pruning every third year may be sufficient.
In March, cut back wood that’s the thickness of a pencil or just slightly larger in circumference to stubs with three or four buds remaining. These are the buds that will likely produce flowers in four to six weeks. When you’re finished, the vine will show serious signs of interference, but don’t worry: all will be well. It’s almost impossible to be too severe with a wisteria.
In July, after flowering is finished, cut back the whippy new growth of the current season, allowing five or six leaflets to remain on the shortened stems. This will control the girth of the vine and prevent the new tendrils from insinuating themselves into screened porches and eavestroughs.
Wisterias require this type of hard pruning to trigger large flushes of flower buds. Be brave and approach the task with confidence. The vine may look quite butchered after its winter pruning, but be assured it will return to lush growth beginning in May.