Clematis

Can anyone proffer some advice on why two out of three Clematis are flowering abundantly in the same garden and the third although it has lots of healthy green vines is not showing any sign of flowering. I am asking this on behalf of a friend who happens to live in Ontario.

She hasn't said what varieties any of them are. I will see if she can send me photo's if you think that would help in discerning the problem. Thanks in advance for any ideas on why.

 

I am sorry I think I have put this thread in the wrong place - better go transfer it to where it should be.