posted 6 years ago
Depending on the size of the area, I have had the best results getting rid of really tough plants by covering them. Black or clear plastic sheets work well. There are lots of materials you can lie over them to kill them. Plastic, carpet, roofing material, sheets of metal roofing, pond liner, any of it works. The drawbacks are that it takes quite a while for the plants to die, and it takes a lot of whatever material to cover large areas. It can take a year or so with really tough plants, but that is still less than the two years you have been trying. I would caution you to plant immediately after killing off an area. It also help to kill an area completely and have some sort of perimeter to keep the plants from moving back in from the sides into your cleared area. You can use mechanical barriers, like tin buried on edge a foot or so deep, or use plants like comfrey that have really good root systems around the perimeter of the area you cleared. Good luck to you.