"carolineh" wrote
Three years ago I bought 2 identical wysteria plants and planted them
either side of my front door (south facing) - one has flourished and is
now in heavy flower. The other (problem) one has just sent one shoot
straight up the support wires (about 5 meters) and is not flowering. I
believe in order to encourage flowers I need side shoots, can anyone
offer advice on how to encourage them, please.

Two wisteria at the front of your house, you must have a huge mansion. I
trust you are OK on ladders and are prepared for all the hard pruning and
tying in needed with these plants.
Yes, you do need to have side shoots to flower and the plant will make them
when it's ready and these should be cut back to a couple of buds in the
winter.
Our wisteria didn't grow much at all for about 4 seasons and then went 20ft
in the fifth, I think we got our first flowers the next season. It now has a
trunk like a tree.
To get one to flower in it's third year probably means that it is a grafted
plant, perhaps the other one isn't which is why it's acting normally.

--
Regards
Bob Hobden
17mls W. of London.UK