Q.Why is my wisteria not climbing?
I have 2 wisterias, one on each side of an arbor. Nothing blocks either one of them, they have the very same growing conditions, literally are less than 2′ apart. One is growing like crazy, crawling right up the arbor; however the other one is not nearly as full and is not climbing at all. I’ve had them a couple years and when I bought them they were, from the ground to top, about 2′ tall or so. One has grown probably another 2′ and the “problem child” maybe 6-9″. Help! What would cause that?

Certified GKH Gardening Expert
The problem child Wisteria may just need help in climbing. I wonder too if the light is a little less on the other side of the arbor. Even just 2 feet apart, the soil and light conditions can be different. While wisteria doesn't require fertilizer, you might want to spread some 5-10-5 fertilizer on the short side.
The article below will help you with training the vine.
https://www.gardeningknowhow.com/ornamental/vines/wisteria/growing-wisteria-proper-wisteria-vine-care.htm