Last year I had this huge patch of mint, about 10 ft by 10, that came out of nowhere but came in handy. Then came winter and NO SPRNG just rain rain rain and now that I can go outside again the mint has been replaced by buttercups, which are cute and I don't mind them but I'm not sure what to expect from them. Are they a perennial? Do they remain a green ground cover through the winter? Any info welcome and thanks in advance.