I’m installing sod in a backyard in Wilmore and wanted to kill the existing weeds and grass before tilling up the soil. Because the home owners have two small children, and pets, they asked me to use an organic alternative to Roundup. After considerable research, I decided to use a product referred to variously as ‘agricultural vinegar,’ ‘horticultural vinegar,’ or ’20 percent vinegar.’ It’s a chemical-free product that is touted as being 80-100 percent effective in killing weeds.
First, I sprayed weeds growing between cracks in my driveway and sidewalk. The results were astonishing. Within an hour all of the weeds had begun to turn brown. Within three hours they all were shriveled. Two weeks later, they still are dead. The vinegar was every bit as effective as Roundup.
However, the results weren’t as impressive when I sprayed the client’s backyard. Within hours a good share of the grass and weeds had begun to die. Within a week, however, some of them pulled a ‘Lazarus’ and returned from the dead. I believe I know the problem, or at least I have narrowed it down to a couple possible factors.
First, a word about Agricultural Vinegar. Ordinary distilled vinegar, which you can purchase at any grocery store, is approximately 5 percent acetic acidic. This isn’t strong enough to kill plants. Agricultural vinegar has four times the level of acetic acid. Agricultural vinegar, at 20 percent acidity, is a non-selective herbicide that kills plants by blocking sunlight. This prevents photosynthesis from taking place, killing the plant down to the root.
Here’s the secret, I believe, to maximize the effectiveness of agricultural vingegar. First, use it on a warm, sunny day. It definitely will work best when the temperature is above 75-degrees, better still at 80-degrees. Second, do not spray plants with agricultural vinegar if rain is in the forecast. When I spot sprayed my driveway to kill weeds, the temperature was hovering somewhere in the upper 70s, and it didn’t rain for several days after I applied it. Unfortunately, when I sprayed my client’s backyard, it was cooler, partly cloudy, and it rained less than 24-hours after I sprayed the grass. So, what went wrong? The temperature? The lack of full sunshine? The rain? Most likely it was all three.
Although agricultural vinegar is organic, don’t think this doesn’t mean it’s totally safe. It’s critical to take precautions when using this product. Most important, be sure to read, understand and follow the directions on the label. It can kill any plant it comes in contact with, so don’t apply it on a windy day. Cover shrubs and flowers before spraying if there’s a danger of the vinegar drifting on them. Wear goggles. You really don’t want to spray vinegar that is 20 percent acidic in your eyes. Keep this in mind: This stuff can corrode metal, so imagine the damage it can do to your eyes and skin. Wear gloves, long sleeves and long pants. If you get any vinegar on your skin, wash it immediately. And, whatever you do, don’t substitute it for plain distilled vinegar in any recipe. It can be dangerous to ingest it.