Answer: Based on your comments the only thing that comes to mind is that the wisteria must not be happy with the soil volume in the medium sized containers. It is difficult to determine whether or not the soil is staying adequately moist but you can dig down a few inches and feel the soil to get an idea if the watering schedule is right or not. If you must keep them potted for location reasons, I suggest larger containers that are not terra cotta or concrete unless you seal the outsides to reduce water loss from evaporative wicking of the moisture by the porous containers themselves.
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