Wisterias may become reluctant bloomers for a variety of reasons. The most common are that seed- grown wisteria that are not mature enough to bloom yet, improper pruning and fertilizing with high nitrogen fertilizer. And sometimes, even if you do everything correctly, your wisteria may become sulky and refuse to bloom. It may take several years to make your wisteria happy enough to start blooming again, but once you do, it can easily produce blooms for 40 years or more. Just remember, if your wisteria has never produced blooms, it may not be old enough. It can take 10 to 14 years for seed grown wisteria to bloom. If you want your wisteria to bloom the same year you plant it, you must buy grafted wisteria or wisteria grown from cuttings.
Prune wisteria in mid-July to early August by cutting back new shoots to 6 inches.
Cut back older woody stems to the ground with a pruning saw. Leave at least 3 to 4 stems per wisteria.
Prune branches that are crossing or rubbing back to the main stem. These branches will not produce flower buds.
Tie your wisteria so that the main stems are primarily growing horizontally rather than vertically. The stems should be horizontal for at least 5 feet before growing vertically. Do not allow stems to grow downward.
Prune your wisteria again in spring after all danger of frost has passed. Shorten side shoots to 2 to 3 inches. Make sure each shoot has 2 to 3 buds.
Fertilize with super phosphate according to package instructions at the same time you prune in spring.