Can we get a picture of the soil? From the image above, looks to be too lean for wisteria. I use 70/30 potting/topsoil to regular bonsai soil when I collected wisteria. They like constantly moist, cool soil. Hot, well drained, won't do. In the wild wisteria grow with their tops in full sun and their roots shaded in the cool moist forest floor topsoil. Keep that in mind when growing them. Use rich organic soil shaded root zone and full sun top.