I have not used glystar(roundup) yet but i have several customers wanting it. The weeds are growing in their rock gardens which are landscaped with assorted flowers and plants. Im not sure about using roundup here. wont it kill everything in the flower gardens? I dont want to ruin their yards. I cant pull by hand either, the gardens are huge. Weedwhaking out of the question, many loose rocks are everywhere. any suggestions?