I can do that where the horsetail comes up out of a sort of ditch at the back of the garden, but it is less easily done where I know that I have planted things that are evergreen or that haven't come up yet like tulips and other spring flowers as well as perennials. Plus I planted a bunch of new stuff last fall that has yet to erupt. I was thinking of strewing mulch over the entire garden as best I can (afford $$) because the plants can easily grow up through this. But, yes, I will sheet mulch as much as possible the area that is the prime source of the invasion. I am also thinking to overplant with vegies, marigolds, garlic etc everywhere I can to get more variety to the soil and to provide less invitation to the invasion by occupying the soil with other things. Really hard to convert to permaculture on an existing garden. I have thought about digging up sections and treating that but it has taken years to get my garden to where it is and I don't have a lot of time to start over.