Natural Weed Killer 1 Ingredients 1 liter of white vinegar 3 tablespoons of baking soda 2 tablespoons of biodegradable dish soap 2 Preparation Pour the vinegar into a large bucket or spray bottle. Slowly add the baking soda, as it will fizz. Mix in the dish soap gently. 3 Application Transfer the solution into a spray bottle. Spray directly on weeds during dry, sunny days. Tip: the dish soap helps the mixture stick to the leaves, while vinegar and baking soda dry out the plant all the way to the roots.