A few years back, a fellow gardener sent me tiny pips of Lily of the Valley. There was so little to them, I didn't think they would survive. Boy, was I wrong! They not only grew, they have spread to the point of being an invasive pest! I've been digging them out, roots and all, but they've grown into some areas where I can't access them well. I've tried RoundUp (which I use very sparingly and only under very limited conditions), but it has been totally ineffective. I've tried cider vinegar, and that hasn't helped, either. After several years of putting up with this nuisance, I'm at the point where I want to be rid of Lily of the Valley, once and for all. Does anyone know of an effective way to get rid of it without having to constantly dig, and without using really hazardous poisons? Is there some way to smother it to death?