Many gardeners recommend vinegar to eliminate weeds without the use of harsh chemicals. However, as many users discover, it is an indiscriminate killer, offing both weeds and wanted grass.
Vinegar works because it contains acetic acid. Most commercially available vinegars contain around 5 percent acetic acid, while acetic acid-containing weed killers often have higher concentrations. Precisely why it works is not entirely clear, but according to Michael D.K. Owen of Iowa State University, scientists believe acetic acid quickly dissolves the integrity of cell membranes in plants, thus destroying plant tissue. That reaction occurs in both weed and grass plants.
Vinegar vs. Acetic Acid Weed Killers
Weed killers with acetic acid concentrations between 10 and 20 percent were effective against 80 to 100 percent of weeds, according to Iowa State University research. The effectiveness of solutions with lower concentrations -- such as found in household vinegars -- were variable. More studies are needed to determine if vinegar is more effective on certain species than others.
Vinegar is unlikely to kill the root systems of most plants, which provide for their regeneration. In other words, if vinegar successfully kills a plant's above-ground parts, it will likely regenerate. A demonstration at Nashua Research Farm also suggested that vinegar is unlikely to be effective on larger weeds and plants.