My Wisteria has almost stopped blooming.When & how should I prune?

you usually prune to produce more growth for the next season like spring. So it would be your preference if you want to prune in the fall and how much.

You should prune it once in July or August and then again in January of February.

I had this question years ago and a grower in Oklahoma told me to prun the roots,just use a shapr shooter to cut the roots, just go about a foot from the main trunk and sink the shovel deep into the ground,youwill know when you find a root,go all around the main plant, mine was pruned in the early Spring,it bloomed that year. this keeps the plant from sending shoots up ,that helps with blooming.Good Luck.

You can do it in August - good luck!