Answer: The most common reasons for bloom to fail are frost damage to the flower buds and improper pruning, sometimes too, overfertilization can contribute especially if they are adjacent to a lawn area that recieves lots of nitrogen fertilizer. (Since your plants are grafted and blooming we know it is not due to being a seedling that is shy to bloom.) Here are some wisteria growing and pruning tips that you may find helpful.
I hope they bloom for you next year!
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