In a May 2002 study by the United States Department of Agriculture, solutions of vinegar that contain an acetic acid strength between 10 percent and 20 percent were shown to be effective at killing common weeds, including pigweed, foxtail and Canadian thistle. Although common household vinegar has a concentration closer to 5 percent, it can still be an effective weed killer. You can mix vinegar with a combination of sodium and detergent to make a solution that is effective on common weeds.
Pull on kitchen gloves before handling chemicals.
Pour a gallon of white vinegar and one cup of table salt into a stock pot. Heat the pot and stir the contents until the salt dissolves. Add 1 tablespoon of dish soap.
Allow contents to cool and pour into a spray bottle.
Time the application of weed spray for early in the morning or late in the afternoon in summer or midday in winter. Plants are involved in transpiration during these times of day, and will absorb the herbicide through their surface and move it through their system and down to the roots. Spray vinegar herbicide onto the leaves of the plant to encourage absorption.