Vinegar, Salt & Dish Soap Weed Killer. Use one gallon of white vinegar, add half a cup of liquid soap and two tablespoons of salt. Shake the mixture. Put the mixture into a spray bottle and spray on the leaves and stems of weeds only, avoiding surrounding plants. According to the Frugal Gardening website, this versatile mixture will kill grass between bricks, as well as weeds in the cracks along the driveway and between sidewalk section.