(Dish soap, vinegar and a spray bottle – all you need for making your own weed killer.) The acetic acid in vinegar “sucks out the water” from the weed, which dries it up. The dish soap helps to break down the outer coat of the plant (cuticle), which helps that vinegar to work best. Below, are two examples from my own landscape of how it worked: Just 24 hours later…. Here is another example: