From another site "The root system of a massive vine wants to be equal in size to the “above ground” portion of the plant. Grown as a vine, Wisteria will outgrow a container quickly. The roots will just need more space to spread out in order to support such a large mass of leaves and flowers." They really are not suitable to a container unless grown as a bonsai where it gets regular root and stem pruning to maintain it as a small tree. If there are holes in the container, it may now have covered or plugged those holes and the water may not drain properly and it's rotting the roots.
