Vinegar as a weedkiller

The claim

Household vinegar is a natural, effective weedkiller.

What the evidence actually shows

Montana State University Extension sets out the position clearly. Acetic acid is a non-selective contact herbicide. It has no translocation to roots and no soil residual activity. That combination defines exactly what it can and cannot do.

What it can do: kill small seedlings, roughly the two- to four-leaf stage, whose growing points can be completely wetted. What it cannot do: control perennials, which - in the extension's words - are unlikely to be controlled because they can resprout from roots.

There is also a concentration gap most people miss. Household vinegar is 5% acetic acid. Commercial herbicidal formulations run 20 to 30%. The kitchen bottle is markedly weaker than the tested product, and the higher concentrations are corrosive materials requiring eye and skin protection rather than a casual spray.

The salt-and-soap version

Recipes adding salt and dish soap to vinegar circulate widely. The soap is a surfactant and does improve wetting. The salt is the problem: sodium chloride does not degrade, accumulates in soil, and damages soil structure and subsequent plant growth. A recipe that sterilises the ground is not a natural alternative, it is a durable soil problem.

What to do instead

Use acetic acid where it fits: young annual seedlings, hard surfaces, spot treatment, with full wetting. For perennials use repeated cutting to exhaust reserves, mulching, or a translocating product. Do not add salt to anything you intend to grow in.