Using Vinegar to Kill Weeds
Q: After reading your article on lawn care in a past TOH issue, I tried out household vinegar as an organic weed control on some dandelions in my backyard. Within a couple of days, they looked pretty dead. Could I use this method to kill the existing lawn?
— Mark, by e-mail
A: Roger Cook replies: Vinegar, or acetic acid, is one of the newest things in weed control. When sprayed on, it has an almost immediate impact, as you discovered. The problem is that it doesn't kill the roots, so some weeds grow back over time.
To kill a lawn completely, you could spray the household vinegar on weeds and grass that are actively growing, and after a few days, follow up with glyphosate (Roundup) on anything still alive; that would greatly reduce the amount of herbicide you need. Or, you could apply another dose or two of vinegar before Rototilling and reseeding. You may get a few weeds, but don't use vinegar or herbicides on them yet. Wait until you've cut the new grass three or four times before launching another chemical attack.