Comparing vinegar weed killer recipes

How Weed Killers Work

Weed killers, both homemade and commercial products, start by killing the above ground foliage. Systemic weed killers, like Roundup, are designed to cause injury to the entire plant including the root system so it will not grow back, according to a guide prepared by the University of California available here. Homemade vinegar-based products lack the oomph of commercial products and only desiccate the above ground foliage.
 
3 Homemade Weed Killer Recipes

A quick search on the internet yielded lots of recipes for homemade weed killer with vinegar the primary ingredient. I pulled out the three most frequently cited recipes and tested the concoctions on weeds in my gravel driveway.
  • Weed Killer Recipe #1: Plain vinegar
  • Weed Killer Recipe #2: 1 quart vinegar + 2 tablespoons liquid dish soap
  • Weed Killer Recipe #3: 1 quart vinegar + 1 teaspoons liquid dish soap + 1/4 c salt
Application

It is important to apply vinegar-based weed killer on a sunny day after the morning dew has evaporated and with no rain in the forecast for at least 24 hours so the solution is not diluted with water. Also choose a time with no breeze or little breeze to avoid floating spray that could land on wanted vegetation, like grass or flowers, since weed killers can kill more than the intended weed. For better control, use a fine stream from the sprayer or, as I did with this experiment, trickle the weed killer onto the weeds so there is no mist floating. The objective is to thoroughly coat the visible foliage.

I selected a location with an abundance of yellow woodsorrel (oxalis). This weed has heart shaped leaves and yellow blossoms about the size of my thumbnail. The plant spreads underground with rhizomes and also propagates with seed.

At 9:00 a.m., while the sun was shining and there was no dew present, I poured the vinegar mixture onto the oxalis until all the leaves were wet.

My Results

In the picture above, a different weed killer recipe was used on the weeds immediately in front of each brick. What you are seeing, eight hours later at 5:00 p.m., is that all three applications showed dried leaves on the oxalis. The leaves were easy to crumble between my fingers. I pulled the weed from the ground and looking closely, I could still see a few bright green stems in recipe #1 (vinegar only) and recipe #2 (vinegar + liquid dish soap) specimens.

Recipe #3 (vinegar + dish soap + salt) was the most effective in killing the weed down to the ground; all the stems were brittle.

With repeated applications to new growth over the course of weeks, the homemade weed killer should eventually eradicate the weeds making vinegar-based recipes a viable form of weed control.