I was wondering the same thing.
I need to spray something safe for kids in the mulch around the kids' play area so the usual weed killer won't work.
I got this idea from a site called Thrifty Fun.I haven't tried it yet.
There are a number of recipes for homemade weed killers. All are variations of the following recipe:
1 gallon of white vinegar
1 cup of table salt
1 tablespoon of liquid dish soap
Mix thoroughly until the salt dissolves, pour into a hand-held spray bottle and spray the solution directly on the target weeds. For weeds growing out of cracks in driveways and sidewalks, some people pour salt directly on the weeds. Other people pour straight vinegar directly on weeds. Still others add a few drops of liquid dish soap to the recipe to help the solution stick to the weeds. The important thing to know about this homemade recipe is that is non-selective. Just like any weed killer, use it sparingly and with caution. Non-selective means it will kill or damage any plants or grass that come into contact with it. Also, try to avoid spraying it directly on the soil. Vinegar breaks down the soil structure and kills beneficial microorganisms. In areas where this is applied, the vinegar can render the soil sterile for several years. Other organic methods of weed control include hand-pulling, boiling water or torching.