Have you had a soil test done where the wisteria is planted? There could be too much nitrogen and not enough phosphorous. If so, you are growing beautiful leaves and no flowers. If you were told to shock the roots, it was to cut the roots to keep it from taking up more nitrogen. Look for a fertilizer with a higher number in the middle (NPK – phosphorous is the P) and use it. Another cause could be not enough sunlight. Wisteria should be planted in full sun. Something else to consider, are you pruning it and cutting off the flower buds? I’ve done that before.
Thanks for writing and let me know if this helps!