By Nickgore
United Kingdom 
Why is my Wisteria no longer flowering?
We have a very old Wisteria which covers the front of our house and the house next door. For the last 2-3 years it has gone from being a mass of flowers to producing mainly leaf and little in the way of flowers though I am still pruning it hard back to 2-3 buds in winter. Any ideas why?
When we moved in 25 yrs ago it had not been pruned other than being savaged with a hedge trimmer and I tried cutting out a lot of surplus branches but there are still far too many. Could it be that there are just too many branches and I need to cut out a lot of the growth to enable it to concentrate its powers where needed?
21 Apr, 2017
Wisteria is a member of the legume family all of which 'fix' nitrogen in the soil. So over the years you can get a big build-up of nitrogen which encourages stem and leaf growth at the expense of flowering.
In early August, I'd cut back as much extraneous growth as possible using a pruning saw where necessary to remove woody branches back to the main stem/s. Also prune back the new long whippy stems you want to keep to about 5/6 buds. I'd feed the base of the Wisteria with Sulphate of Potash only and water it in well.
In early January further shorten those pruned stems back to 2 or 3 buds. Hopefully that will produce results.
21 Apr, 2017