I have a wisteria vine that I planted last year that is turning yellow. Is part of some cycle? Is it supposed to turn yellow and shed in the winter, or something wrong?
Where are you located? Usually yes wisertia is a deciduous vine(meaning it loses its leaves int he winter), although you do see it trained into a tree form. It may stay evergreen as some azaleas that lose theirs leaves up here, do in the south.
Wisteria is deciduous. I'm thinking that you may have had some cold weather and that triggered the leaf drop. If that's not it, then look at the pH of your soil. If it's alkaline that could be the problem as wisteria prefers a more acid soil.