As I sat looking up at the Wisteria that is in need of trimming this it what I SPIED!
Severe pruning, if needed, is done during the winter dormant season months of November, December, January and February. Some July pruning can be done, to help control the rampant growth of the vines. Otherwise, you end up with a tangled mess of intertwined vines. The dormant season pruning is the severe pruning, when one should cut the leader vines back to the desired height. Then prune the side shoots (those growing from the main leaders) back to the second or third dormant bud. This is where good judgment must be used, because the flower buds form the previous summer, and if you prune too severely, of course you will be cutting off all the potential new flower buds. I think the most important consideration is proper pruning at the correct time. If allowed to grow unattended the vines may reach 50 feet or more.