Cheap, Natural, Easy Weed-killer?
Salt, and/or Vinegar!
I tried both, and they both are doing the trick. I liked the apple-cider vinegar the best- it totally killed it on the spot. (I'm not a fan of the vinegar smell, but since it's outside it's only a brief encounter). Salt apparently makes it really hard for anything to grow anytime in the future too. So, not good for garden beds-- but perfect for sidewalk cracks!