The standard recommendation for lawn care is to remove 1/3 of the leaf blade with each mowing. That leaves plenty of the leaf to photosynthesize and support the roots. Grass plants managed in this way are strong competitors with weeds for mineral and water resources.

So, if you apply a standard weed and feed, and remove 1/3 of the leaf blade with each mowing, you should be safe to compost grass clippings from the fourth cutting after the application.

Herbicidal vinegars are 20% solutions of acetic acid– 20% vinegar, 80% water. Acetic acid of any concentration is considered a weak acid in chemistry-speak, but herbicidal vinegars are strong enough to cause skin irritation, and medical attention should be sought if it gets in the eye. By comparison, white vinegar used for cooking is 5% and cleaning vinegar is 6%.

Herbicidal vinegars are not selective, so take care to avoid overspray to desirable plants including grass plants. Also, the soap-vinegar combo can harm desirable plants when temperatures rise or if applied under full sunlight conditions.

It would be safe to compost plant materials that have been exposed to herbicidal vinegars. Organic acids are a natural by-product of the composting process, although composting microorganisms will have further broken down these acids in mature composts.