Seed-grown wisteria is notorious for testing a gardener’s patience, and even vegetatively propagated plants can be recalcitrant. Pruning hard is recommended, and some people try to shock the wisteria (threatening death!) by cutting into the root system partway around the plant…sort of in-place root pruning. Martha Stewart told a funny (not) story about her wisteria standard at Turkey Hill, and how it wouldn’t bloom years ago. She was advised by an expert to hammer on the trunk to send the signal to the plant to bloom via some mechanism or other (whether hormones or terrorism I don’t know!) and she did so. Voila! it bloomed the best it ever had…and then proceeded to drop dead. One other tip: Don’t feed it Nitrogen.