How can I kill my wisteria plants, & make them not able to come back?

You can cut the plants down to a stump. drill holes into the centre of the stump as deep as you can without drilling through the side of the stump. Fill with a strong weed killer. cover with tin can or whatever you have so birds, animals, children can't dabble in it. We used this method on the stumps of our Atlantis tree that is related to the wild Sumac that grows all over here. Both of these plants spread all over because of their running roots. We had to use a second dose of the weed killer and then it worked! So if you drill as far into the trunk root as possible you may not have to apply the weed killer a second time. We used "Round Up". This brand may not be available now, so if not...find a strong weed killer.

cut them to the ground and then dig them out....this is what I am planning to do with a large gardenia bush...jan

Unless you use Round Up they will continue to grow up again every spring. Round Up penetrates down into the ground to kills the roots. This is the only way that a plant can really be prevented from continuing to grow. Don't waste your money and time with any other product claiming to be eco-friendly, green, or any other of these current terms. They will only kill the part of the plant growing above ground.

Salty water will kill most any plants.Use Ice cream salt or Kosher salt for best results.But be aware that nothing else will grow in the spot for a long while .And grass will die as well.

The best is to get rid of their roots.