Vinegar - The Organic Herbicide
USDA greenhouse and field research have been conducted at Beltsville, Maryland, to determine the efficacy of vinegar for controlling weeds. The results indicate that vinegar can kill several important weed species at several growth stages. Vinegar at 10, 15 or 20% acetic acid concentration provided 80-100 percent kill of selected annual weeds, including giant foxtail up to 3 inches in height, common lambsquarters up to 5 inches, smooth pigweed up to 6 inches, and velvetleaf up to 9 inches. Control of annual weeds with vinegar at the 5% acetic acid concentration was variable. Canada thistle shoots were highly susceptible with 100 percent kill by 5% vinegar.
ALWAYS add high-percentage acetic acid (or any strong acid) to water to prevent the possibility of dangerous spattering, NEVER the reverse.