Why doesn’t my wisteria bloom?
Note from Neil: I get this question scores of times every year, so I’ve had a lot of experience helping people figure out the source of their frustration.
There seldom is one definitive answer. Wisterias need full or nearly full sun to bloom best. Do not prune them during the winter. (They set their flower buds in late fall, and winter pruning removes them.) Avoid high-nitrogen fertilizers near the plants from mid-summer on. You might try root-pruning by severing lateral roots with a sharpshooter spade 18 to 20 inches out from the trunk in September. That may trigger bud set.