Garden Myths - Learn the truth about gardening

Vinegar Weed Killer Myth

Weed killers have been banned in a number of Countries including Ontario, Canada and people are now looking for natural week killers. Does vinegar kill weeds? Is it a natural weed killer? Let’s have a closer look at this common garden myth.

Vinegar weed killer myth

Vinegar weed killer myth

Vinegar Weed Killer

What happens when you pour vinegar on a weed? For most plants, the vinegar is so acidic that it damages the green leafy part of the plant. Within a day, the plant withers and the leaves go brown. It certainly looks like vinegar has done the job.

If you re-read the above sentence you will notice that it only talks about the green leafy part of the plant. What about the plant below ground? Turns out that vinegar has almost no affect on the root system. When vinegar reaches soil level it is quickly neutralized so that it is no longer acidic. The acetic acid in vinegar is converted to harmless acetate salts which have little effect on the weed.

The weed just regrows and in a week or so, the weed is back. Vinegar is not a natural weed killer.

Does Strong Vinegar Kill Weeds?

Vinegar is about 5% acetic acid, the rest being water. Pickling vinegar is about 7% acetic acid, but even this is not strong enough to kill weeds.

A higher concentration of acetic acid will kill some plants, but you need to use at least 20% acetic acid.

Some sources still call this vinegar, and I suggest that this is a bad idea. We all know vinegar as something that is fairly harmless. 20% acetic acid should be considered to be a dangerous chemical. Make sure you wear gloves and eye protection when using this chemical. In this blog the term vinegar is used to refer to a product that is at most 7% acetic acid.

You will not find 20% acetic acid in the grocery store, but there are some commercial natural weed killer products on the market that contain this higher amount of acetic acid. There are also several products on the market that don’t have 20% and they are not worth buying – use pickling vinegar instead.

Will 20% Acetic Acid Kill Weeds?

20% acetic acid will kill small annual weeds but has limited effect at killing larger annual weeds. It only kills some perennial weeds and is not effective on grass weeds. The reason is fairly clear. Acetic acid does not affect the roots. The roots of large annuals, and most perennials allow the plant to grow back.

What About Repeated Use?

In my statement above I said that vinegar only damages the green leafy part of the plant. Let’s look at how this affects the plant. The plant has used its internally stored food reserve to grow the leaves. They are now ready to absorb sun light and make more food. You come along and damage the leaves to the point where they are no longer useful to the plant. The plant now has to use more stored food to regrow new leaves. If you come along again and kill them off, you will weaken the plant even more. Over time this will kill the plant.

The secret to making this work is repeated applications that are timed close enough together that leaves never produce food for the plant. Go on vacation for a couple of weeks, and you can start the process all over again. Most of us are just not diligent enough to make this work.

Seedlings that do not yet have a good root system can be killed with a single application of vinegar.

Vinegar is also non-specific. It will damage any green plant including grass and most other living organisms.

 Is Vinegar Weed Killer a Myth?

So is this a myth or not? Vinegar will kill weeds and so strictly speaking it is not a myth. However, a single application will only remove the leafy parts and not kill the plant. Unfortunately most references only talk about the 5% vinegar and one application, so their recommendation won’t work – they are perpetuating a myth.

References:

1)  Vinegar for Weed Control Revisited: http://www.weeds.iastate.edu/weednews/vinegar.htm

2) Vinegar as a burn herbicide: http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=195808.

3) Photo Credit: Joe Shlabotnik

Robert Pavlis
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writting and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

19 Responses to 'Vinegar Weed Killer Myth'

  1. Justin Cuff says:

    In 2011 the product’s manufacturer, Monsanto, agreed with the New York Attorney General’s office to discontinue their use of the terms “biodegradable” and “environmentally friendly” in ads promoting Roundup. Why? Because these terms were false. Roundup is neither biodegradable nor environmentally friendly.
    http://ecowatch.com/2015/03/23/monsanto-roundup-glyphosate-cancer/

    • Your reference has nothing to do with the point you are trying to make, and ecowatch is not a reliable source of information. WHO has deemed Roundup as a carcinogen – it also considers the alcohol we drink as being carcinogenic.

      It is true that “Monsanto, agreed with the New York Attorney General’s office to discontinue their use of the terms “biodegradable” and “environmentally friendly” in ads promoting Roundup”. However “Monsanto maintains that it did not violate any federal, state or local law and that its claims were “true and not misleading in any way.” The company states that they entered into the agreement for settlement purposes only in order to avoid costly litigation. “as per https://www.organicconsumers.org/old_articles/monad.html

      Is Roundup biodegradeable? What does the term mean? It is defined as ‘capable of decaying through the action of living organisms’. In fact glyphosate starts degrading in as little as 30 days in the soil, and this degradation is due to the action of bacteria. Therefore glyphosate is definitely biodegradeable. As pesticides go, it actually degrades faster than most.

      Is it environmentally friendly? This term is much harder to define. It implies a degree of friendliness, and there are no precise measurements for the degree of friendliness. So anyone can say anything is environmentally friendly or not, depending on the criteria they use. I can easily argue that no manufactured product is environmentally friendly – they all use non-renewable resources. However, when you compare the effects on the environment of Roundup compared to older herbicides, it is definitely more environmentally friendly than other options.

  2. rogerbrook says:

    I fully support your comments to the gentleman who is foolish enough to put salt on his soil!
    All the prejudice against glyphosate make me despair.
    I was interested in your comments about the strength of vinegar. I have considered using it against liverwort a primitive weed which my wonderful Roundup does not kill.

    • I also found that Roundup is not very effective on moss, and the hen & chicks plant. Strong vinegar does brown off the green parts, and I suspect liverworts don’t have much of a root system – so it might be effective.

  3. Donna says:

    I read that 20% vinegar injected into the tap root of weeds will kill them. (injected with a syringe)

    • I really do not see this as a viable weed control system – but I would be interested in a reference showing this.

      • CaptainAwesomer says:

        I had the same idea a couple years ago, filled up a giant syringe with vinegar, tried injecting it into weeds (dandelion and thistle). It didn’t work. I got the needle in but couldn’t inject the vinegar, it just doesn’t absorb. It all dripped back out.

        Also tried spraying cleaning vinegar on weeds, it just browned them and stunk for a week.

        My conclusions were: only roundup kills thistle, spraying 2,4-d (or plucking by hand) kills anything leafy, and weed-b-gone is a complete waste of money.

  4. Carrie says:

    I have been using a vinegar/salt/Dawn solution for a 3 years now and it works! I live in the Pacific Northwest. This mixture works best on hot dry days, and when used nothing will grow in the same spot for years. When I first used it on a large weed in my grass, the grass around it also died. And after 3 years, I still have a yellow ring of dead grass where I sprayed.
    In the past, I used to spray Roundup every month to kill the constant weed patches on the edge of my gravel driveway. And the weeds kept coming back! Tired of the toxic chemicals and the expense of Roundup, I searched for an alternative.

    Here’s the recipe:

    1 Gallon white distilled vinegar (I get Four Monks brand from Costco)
    http://www2.costco.com/Browse/Product.aspx?prodid=11073510&whse=BD_115&topnav=bd

    2 cups salt (I use Diamond Crystal Water Softener from Home Depot)
    http://www.homedepot.com/p/Diamond-Crystal-Solar-Salt-40-lb-Extra-Coarse-Water-Softening-Salt-100012454/100172669

    1/4 cup Dawn Ultra Dishwashing Liquid (Blue)
    http://www.homedepot.com/p/Dawn-Ultra-56-oz-Original-Scent-Dishwashing-Liquid-003700011045/100674012

    You don’t have to use these exact brands (except Dawn Ultra I think), I’m just showing you what I use.
    When I use it on the weeds growing in my gravel driveway, I get no weeds the following spring. I have used this mixture during overcast, cooler days in late summer with poor results so the heat and dry weather is a factor. FYI, this mixture works within minutes.

    Here’s the recipe:

    1 Gallon white distilled vinegar (I get Four Monks brand from Costco)
    http://www2.costco.com/Browse/Product.aspx?prodid=11073510&whse=BD_115&topnav=bd

    2 cups salt (I use Diamond Crystal Water Softener from Home Depot)
    http://www.homedepot.com/p/Diamond-Crystal-Solar-Salt-40-lb-Extra-Coarse-Water-Softening-Salt-100012454/100172669

    1/4 cup Dawn Ultra Dishwashing Liquid (Blue)
    http://www.homedepot.com/p/Dawn-Ultra-56-oz-Original-Scent-Dishwashing-Liquid-003700011045/100674012

    You don’t have to use these exact brands (except Dawn Ultra), I’m just showing you what I use.

    • So you use this concoction, and nothing grows in that spot for 3 years? Do you think you might have poisoned the soil? The sodium in the salt is highly toxic to plants. You have effectively contaminated your soil to such an extent that nothing grows. That might be Ok on a patio, but salt is very soluble. Each time it rains, some will be washed into your garden contaminating the plants that grow there.

      It does not sound like a good solution to me.

      It is the salt in your mixture that is killing plants, not the vinegar.

      • Tony Ventura says:

        Robert….you sound to me like a shill for Monsanto. If a person has an area that they want to be weed free, like the op mentioned a gravel driveway, I find it highly unlikely, given the mixture that a significant amount of salt is going to leach anywhere. Your position that you are ‘poisoning’ the soil is spot on. This is exactly what one wants to do when preventing weed growth. This is a tremendously superior alternative to poisoning people by using something like Roundup. Naturally though, one could never use this concoction near desirable plants, but this practically goes without saying.

        • Sodium chloride is very soluble. The sodium ion is the issue here. Every time it rains sodium will travel along with water. If the water from the driveway goes into a garden or onto the lawn, the sodium will also travel to these areas – poisoning the soil and making it hard for things to grow. If it runs directly into the street sewers, or it just percolates down, it will eventually pollute our rivers and lakes.

          Since sodium is a stable element it does not degrade – it will be somewhere for ever.

          Roundup on the other hand has a fairly short half life, and quickly degrades. It also sticks to soil and stays put until bacteria degrade it into harmless chemicals. It does not wash away with the rain.

          The toxicity of Roundup is extremely low – vinegar is more toxic. It is not as you say “poisoning people”. Your car exhaust is many times more toxic.

          Why is it that anti-Roundup people think that anyone who uses the product is being paid by Monsanto?? It seems to be one of their few arguments against the product.

          • Michelle says:

            How is vinegar more toxic when it is used in cooking and can be ingested; can you or would you use Round-up for cooking?

          • One way to measure toxicity it to feed varying amounts to animals. The amount that kills 50% of them is called the LD50 (Lethal Dose 50%). for the sake of humans they use rats which are biologically and biochemically quite similar to humans. When they do this with vinegar and glyphosate they find it takes more glyphosate to kill 50% of the rats than for vinegar. Therefore vinegar is more toxic.

            Cooking with Round up has nothing to do with it – why would you use a different chemical for cooking? But when you do use vinegar for cooking or eating, you use very small amounts, and so it is safe to eat. the dose is everything when it comes to toxicity.

      • CaptainAwesomer says:

        So what would you use to kill weeds and poison soil? Is there something that lasts a long time but doesn’t travel far when it rains?

        I have a brick patio in my backyard with grass and weeds growing through. I’ve blasted them out with a pressure washer, killed them with RoundUp, yellowed them with vinegar (they were back to normal two weeks later). But new weeds and grass always show up.

        • Concrete. Any chemical product will either degrade, or wash away. it is part of having a brick patio.

          I have a flagstone pathway, and weeds grow between the stones. I use a string trimmer to cut them down. they grow back, and i cut them again – it is part of gardening.

  5. Sherry Rieder says:

    What kills poison oak?

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