We garden on sandy soil. The wisteria at the front of the house has had many white flowers. The blue one at the back had one feeble flower and it had been fed chicken pellets and cosseted.
Maybe ignoring them is the best thing.
As for pruning I give them a haircut after flowering. I would plant a vigorous one in the hope that you get results. My little mini one gets smaller every year. It has nearly disappeared!
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