Getting rid of weeds tops most people's list of least favorite garden tasks, and using chemicals to reduce the work is tempting. Most herbicides have environmental consequences we may not wish to risk, but vinegar, a common acetic acid solution, is both natural and environmentally safe. Both homemade solutions and commercially available vinegar-based herbicides are effective.
The Composition of Vinegars
Vinegar, the household kind used in salad dressings and pickles, is a 5-percent solution of acetic acid not strong enough to do much damage but can irritate your skin and eyes. Most household vinegars are produced by bacteria from the fermentation of apple cider, wine, rice or other food.
Slightly stronger solutions, up to 8 percent, have much the same effect and, because they are considered to be minimum risk herbicides by the EPA , they do not need to be registered. Stronger concentrations must be have EPA approval because, at 11 percent, they can burn skin and cause permanent eye damage. Solutions of 20 percent or more must be applied with goggles or face shields, waterproof gloves and long sleeves and long pants.
Types of Vinegar-based Herbicides
Some EPA approved herbicides with 20 percent or 25 percent acetic are available, including EcoSharp Weed & Grass Killer and Weed Pharm RTU. Others include citric acid plus vinegar and other ingredients, such as clove oil, thyme oil and garlic. Always check the percentage of acid in a formula to judge the effectiveness before you buy.
The effectiveness of a vinegar herbicide depends on the strength of the solution, the age and type of plant, and the percentage of leaf surface covered. At 20 or 25 percent, the solution is usually effective on most weeds of any age. At 5 to 11 percent, vinegar is only effective on very young plants, those with only a few leaves, or on particularly susceptible varieties.
Vinegar and higher concentrations of acetic acid are applied with a sprayer to the leaves of the weeds, coating them completely. Spray on a warm, dry day when so that rain will not dilute or wash away the solution and avoid windy days to avoid spray onto ornamental plants, which could be damaging. Follow recommendations on the product label for skin and face protection.
Acetic acid is a contact herbicide and kills the cells of leaves. Effects are seen quickly, usually with in 24 hours, but only the leaves are affected. Plants with deep perennial roots, such as dandelions and thistles, will regenerate their leaves and would need to be sprayed many times before dying.
As a contact herbicide, the product must stay on the leaves long enough to kill the cells and a good rain soon after spraying will wash the solution off, canceling the effects.
Strong solutions of acetic acid will lower the pH of the soil temporarily. It will, however, return to normal within a few days.