Answer: You would be absolutely amazed if you knew how many folks have this problem (or maybe you wouldn't since you are going through it yourself). It sounds like you have tried all of the remedies out there except root pruning, and I believe that is exactly what you should try next. Root pruning, in my opinion, is best done in the spring. When done in the spring, your plant has a whole growing season to recuperate. Root pruning is accomplished by slicing the roots with a sharp spade in a circle about 1' deep and about 2' from the stem. When you do this, add some of that superphosphate in to the trench, just beyond where you have severed the roots. Guess what though? This still may not work. I have heard of wisteria flowering once and then not doing so again for 20 years! It is a beautiful but stubborn, stubborn plant.
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