I have often been asked whether vinegar was a good weed killer. I have thought it had potential, but it has been my understanding that the weak vinegar solution we use in cooking is probably not strong enough to work well. Now, recently, I have been sent a sample of a weedkiller, containing 8% clove oil, 90% vinegar, and 2% lecithin. It is called Perfectly Natural Weed and Grass Killer. I have been using it on the weeds in the sidewalk cracks in front of my house. It has worked well on annuals, and has killed some of the perennials, like dandelions, but a couple of those have recovered. I tried it on them again today, a third time, ever hopeful.
The vinegar in Perfectly Natural Weed and Grass Killer is 8% acetic acid, quite a bit stronger than ordinary vinegar, and, no doubt, harmful even to get on ones skin in that concentration. The lecithin is a food product used to emulsify, that is, mix oil and water, so it probably just keeps the clove oil in suspension. Interestingly, the clove oil is listed as the active ingredient, the vinegar as an inert, or inactive ingredient, though I'm sure it has an herbicidal effect.
My web research tells me that this is a Canadian product, and that Home Depot will be carrying it in the U.S.. A Colma Home Depot worker tells me they don't have it or know about it, but that they have had several queries about it this week.
A similar product mentioned on the web is Burnout II, which is 4% clove oil, and also contains vinegar, citric acid, lecithin, sodium laurel sulphate, and mineral oil.
A study that compared several herbicides, including the herbicide Roundup (which contains the synthetic compound glyphosate) and Burnout II, found that these two products produced similar results, however while the Roundup cost $80 an acre, the Burnout II cost $1200 an acre. This is dramatic. Though I didn't buy my Perfectly Natural Weed and Grass Killer, I supect the price of it is similar to Burnout II, however, since I am using it only on weeds in cracks where I can't pull them, I won't need much of it to do the trick.
In summary, either of these vinegar and clove oil based herbicides are reasonably effective unselective herbicides and, unlike Roundup. they don't introduce synthetic chemicals into the environment. If I can figure out where to buy more of this kind of herbicide, I will do so.