Thank you for waiting. Failure to bloom is the most common problem gardeners have with wisteria. These plants are generally easy to grow, but are very touchy when it comes to blooming. There are several possibilities. First of all, make sure when you prune to keep the plant under control that you are not cutting off all of last year's growth. Wisteria's bloom on the previous year's growth, and if it is removed, there will be no flowers. It's best to prune shortly after the plant blooms - or should have bloomed.
Wisterias need full sun. Too much shade results in no bloom. Perhaps some other tree in your yard has grown so big over the years that it now shades the wisterias.
Too much nitrogen is another common cause of failure to bloom. Root pruning is recommended to prevent the plant from taking up too much nitrogen. To do that, you take a shovel and cut down in a circle around the tree, severing roots all around it. This seems drastic, but it does work many times.
Lack of phosphorus is also common. Wisterias need a lot of phosphorus to bloom. You can buy a superphosphate fertilizer at a garden center or a nursery. These fertilizers must be applied in the fall. If you put them down in the spring, they won't promote bloom at all. You can still do that this fall if your ground hasn't frozen yet.
Wisteria that has been grown from seed instead of cuttings often blooms poorly or not at all. In that case, nothing can be done because it is an inbred trait. however, since yours have bloomed in the past, this isn't likely to be your problem.
Here's a reputable site where you can read more about wisteria growing:http://www.hort.purdue.edu/ext/wisteria.html
In summary, I would be sure not to prune off the previous year's growth and apply a superphosphate fertilizer. If another tree has begun shading your wisterias, consider pruning it. If you feel comfortable with it, root prune the trees.
If you have more questions, let me know by clicking on REPLY. I wish you success in inducing blooms.