Vinegar Weed Killer vs Roundup

Vinegar will kill weeds? Yep! A recipe for vinegar weed killer is posted on several gardening sites. The problem is, it is not a very effective herbicide.

The lack of weed control options has been very frustrating for organic farmers, gardeners and homeowners who do not want to use synthetic pesticides.

Spraying Weeds with Weed Killer

The idea of using household vinegar as an herbicide is very appealing, it's natural, inexpensive and readily available, but household vinegar is not strong enough to kill most weeds while horticultural vinegar will burn down many.

Horticultural vinegar works very well on annual weeds that will not re-sprout from underground roots or shoots and perennial weeds that are less than 3 weeks old. It is an option to consider for non-selective weed control. However, in most places that a gardener would apply non-selective weed control, a mix of annual and perennial weeds are present and there are better, safer options.

"But vinegar is not an herbicide!" Well...technically, any substance used to deter, damage or destroy weeds is an herbicide.

How Vinegar Works as a Weed Killer

The acetic acid in vinegar is the active ingredient. When applied to plant foliage, the acetic acid destroys cell membranes causing plant tissues to dry out. Acetic acid does not move through the plant so only the foliage of treated weeds are damaged or killed, the roots are not affected.

Vinegar-based herbicides are contact and non-selective, which means any plant foliage that is sprayed will be damaged. These products can be used to kill weeds growing in patios, walkways, driveways and landscape beds. If used in lawn areas, carefully apply to weed foliage only or surrounding grass will be damaged.

Tips for best results: Apply vinegar on hot, sunny days. It works great on young (less than 3 weeks old) and rapidly growing weeds.

Why Homemade Weed Killers Are Not a Great Idea

The problem with "home remedies" is that they often haven't been thoroughly tested toxicologically and their impact on non-target species is undetermined, making them potentially more hazardous than synthetic pesticides that are legal. Furthermore, these products are rarely tested in a systematic way for efficacy. Instead, only anecdotal evidence is cited, claims that tend to make the product sound too good to be true. ~ Dr. Timothy W. Miller, Weed Scientist, WSU

Yes, it's an environmentally friendly, natural weed control option, but mixing up a home brew of vinegar weed killer is not the best idea (or very effective). It is better to purchase a product that is labeled for organic weed control such as Weed Pharm.

(For more information, here's a link to Weed Pharm at Amazon.)

It is better to purchase a product labeled for weed control because:

  • The higher the concentration of acetic acid, the better it will work. Kitchen grade vinegar is only 5% acetic acid and is not a very good weed killer. Horticultural vinegar is much stronger -- 15 to 20% acetic acid -- and a much more effective herbicide.
  • "Yeah, but I have a recipe that includes molasses, dish soap and citric acid." USDA ARS research has found that additives do not increase weed control. The percentage of acetic acid and volume applied to weeds determined effectiveness.
  • Using kitchen vinegar or any other material that is not labeled to be used as a weed killer is a violation of FIFRA -- the federal law governing pesticides -- it's not advisable. Vinegar-based products that are labeled for weed control can be purchased from garden centers, farm stores or online retailers.
  • WARNING: Handle with care! The acetic acid in vinegar is an acid and acid is corrosive. Any solution above 5% acetic acid must be handled with care, it can burn skin and cause eye damage. I have heard terrible stories of people spilling acetic acid on themselves.

Why Glyphosate (Roundup) is a Better Choice

Although not organic, glyphosate is a more suitable choice for non-selective weed control. Contrary to the opinion of the uninformed, it is also safe to handle and won't harm the environment -- when used according to the label directions.

  • Horticultural vinegar products carry the Danger signal word on the label, while Caution is found on glyphosate. 20% acetic acid is not something I want to handle, glyphosate is much safer for the applicator.
  • A single application of horticultural vinegar will kill many annual weeds but perennial weeds need to be retreated frequently. A single application of glyphosate will eliminate most weeds, killing them down to the roots.
  • When applied according to the label, glyphosate will not harm the soil or pollute water supplies. It cannot leach into and contaminate ground waters because it forms a strong chemical bond with soil particles where it quickly breaks down into harmless elements.

Organic gardening is a very noble pursuit and I'm very much in favor of reducing or even eliminating chemical usage. Vinegar weed killer home brews made from food grade products are not very effective. Glyphosate is safer to handle than horticultural vinegar, and a much more efficient herbicide. If used according to the label, glyphosate is safe to use around homes and will not harm the environment.

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