The person who lived here before me liked plants, but planted the wrong ones in the wrong places. I'll be pulling peppermint forever. :(

She planted pine cone ginger right next to the wall. I dug most of it out, but some of the tubers spread underneath the wall and are coming up from there. There is no way to dig them out, and I'd prefer not to use RoundUp in the soil. Do you think painting the leaves with weed killer will work to kill the tubers? Someone suggested copper sulfate, but again -- poisons the soil, although it does leach out pretty quickly.