Scientists find a stinky weed killer
Many home gardeners and farmers experiment as often as scientists do. But as valuable as the gardeners' and farmers' experiments are, their results are usually called "folklore," not science.
Gardeners and farmers often want scientists to test their folklore to see if it really works. That's what happened with organic farmers and gardeners who discovered that common household vinegar kills weeds.
These individuals started using vinegar instead of chemical weed killers--and recommending it to friends. Not all of the gardeners and farmers were entirely convinced, though, and some had questions that the scientists could best answer. Like, would vinegar ruin the soil because it is such a strong acid?
Three Agricultural Research Service weed scientists in Beltsville, Md.--Jay Radhakrishnan (formerly ARS), John Teasdale, and Ben Coffman--decided to do scientific experiments to find out.
They knew that if it worked, vinegar would be great for farmers and gardeners who choose not to use most weed-killing chemicals, called herbicides.
They tested vinegar on five major weeds. One of these was Canadian thistle. You may have noticed it growing on the side of the road or in your own backyard around walls or the patio.
In a greenhouse, the three scientists hand-sprayed the thistle with different mixtures of vinegar. Typical white vinegar bought from the store was the weakest mixture--95 percent water and about 5 percent vinegar.
In tests, though, this solution was enough to kill Canadian thistle, giant foxtail, smooth pigweed, and two other weeds up to 2 weeks old. The vinegar caused the young weeds' leaves to shrivel up, turn brown, and die.
But older plants needed stronger vinegar solutions--sometimes more vinegar--to finish them off.
For example, against older Canadian thistles, the scientists found they had to drench the pesky plants' roots to totally kill them. Just spraying the leaves didn't quite do the trick.
The scientists also did a little testing on cornfields. They found they could kill most--or all--of the weeds there without harming the corn. Their tests also showed that vinegar only makes the soil slightly more acidic, and only for a few days.
The weed scientists are glad the farmers and gardeners discovered vinegar as an organic weed killer. And the farmers and gardeners are happy to receive scientific information about how to use it best.
"Usually scientists are the first to discover things like chemicals that kill weeds," said Teasdale. "But this time, it was the opposite of the way it usually works. The farmers and gardeners discovered this natural weed killer. We scientists came in toward the end, with proof about how effective and safe it is."