If your Wisteria plant is forming flower buds but they are not opening it most likely to be a nutrient problem i.e a lack of magnesium so try feeding your wisteria in early spring with some liquid tomato feed and also some epson salts 4 teaspoons to a gallon of water. Both these items contain magnesium.
In addition to this its worth mulching the base of your wisteria with some very well rotted garden or farmyard manure as a mulch