Read the bleach label. Does it or does it not answer your question? The bottle I have in front of me states:"DO NOT use or mix with other household chemicals, such as toilet bowl cleaners, rust removers, acid or ammonia containing products." In case you don't know: vinegar contains acetic acid. Life skill: before you take random advice, have a pretty good reason to trust the person giving it to you. The person giving you this advice may not be an idiot; it's possible s/he's just an idiot when it comes to chemistry...or perhaps s/he is out to get your job. Mixing vinegar with chlorine bleach generates chlorine gas. Chlorine gas is a poison gas. Poison gas kills people. Interestingly, the chlorine poison gas used in the First World War killed very few, but injured many - mostly blindness and (often permanent) lung damage. Salt and bleach might kill weeds, but it will kill most other plants, too. And could hurt any animal that touches it. If you want a "very powerful and highly effective" weed killer, why not just pour gasoline onto the area and light a match? At least then you won't leave behind an area where little or nothing will grow (salt makes soil infertile). Once it's burned off, it's gone (well, any left might cause cancer, but don't sweat the small stuff...). [I'm hoping I don't have to tell you not to do this...] In all fairness to your co-worker, I just mixed some of bleach with vinegar and while it did generate chlorine gas, there wasn't much generated. You might be able to do this without killing yourself, especially if you did it in a well ventilated area. Although I only tried it with a couple of tablespoon fulls, I suspect using a gallon would still not be lethal. I sure wouldn't try it. Nor do I think it would make a particularly effective herbicide. If you really really need to check this out, forget the vinegar, buy some thickened chlorine bleach (will better cling to leaves) and mix with salt and use that. I have no idea what it will do. Its possible that any animal seeking salt will be (severely) hurt, and it will damage lots of surfaces it comes in contact with. But I'd expect (I don't know, I've no experience nor direct knowledge on this) that it would kill the leaves it was on (I would expect the plant to survive). But its safe enough (unless children are around) for you to try that. Keep away from adding cleaners containing acid, including vinegar, and keep away from adding ammonia.