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Vinegar: More than just a salad dressing?

A Sci4Kids story by Don Comis

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.

They 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.

They started using vinegar instead of chemical weed killers and recommend it to friends. Not all of them 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 (ARS) weed scientists in Beltsville, Maryland--Jay Radhakrishnan, 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 in your own backyard, around walls, the patio or on the side of the road.

In a greenhouse, the three scientists hand-sprayed the thistle with different solutions 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 to finish them off. For example, against older Canadian thistles, the scientists found they had to drench the pesky plants' roots in order 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 Dr. Teasdale, one of the three ARS researchers. "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."

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-- By Don Comis, Agricultural Research Service, Information Staff

Definition: An "organic" farmer or gardener would generally avoid using pesticides, fertilizers or other farm products that contain factory-made chemicals. Instead, they'd prefer nature-based ingredients and/or methods of fighting weeds, growing crops or raising livestock. Click here to return to sentence.