Commercial weed killers have been banned in a number of Countries including Ontario, Canada and people are now looking for natural weed 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
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 killed the plant.
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 root below ground? Turns out that vinegar has almost no effect on the root system because it is a contact herbicide that is not absorbed by the plant. When vinegar reaches soil level it is quickly neutralized and 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.
Researchers at the USDA (United State Department of Agriculture) found that 5% and 10% concentrations killed the weeds during their first two weeks of life. Older seedlings and more mature plants were not killed.
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 and 30% is even better. This is a good option from Amazon (affiliate link).
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, but 20% acetic acid is a dangerous chemical. This material should be called “horticultural vinegar”. The USDA has even issued a warning “WARNING: Note that vinegar with acetic acid concentrations greater than 5% may be hazardous and should be handled with appropriate precautions.” 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 because they are no better than pickling vinegar.
Does Vinegar Harm Lawns?
Many of the web sites that promote vinegar or the salt + vinegar mixture described below, show pictures of spraying it on lawns as in the image below.
Vinegar is a non-selective herbicide – it can harm all plants including the lawn. It won’t kill it, but it will turn it brown.
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 unharmed roots of large annuals and most perennials allow the plant to grow back.
Pros and Cons of Horticultural Vinegar
The University of Maryland Extension developed this list of pros and cons for using it.
Pros
- Kills some weeds rapidly, causing death in 24 hours.
- Effective for killing annual broadleaf seedlings.
- Vinegar biodegrades and breaks down quickly provided it is not mixed with salt.
Cons
- Permanently kills only broadleaf weeds; grasses and perennials grow back.
- Doesn’t harm roots.
- Needs multiple applications to be effective.
- Nonselective, will harm or kill your good plants as well.
- Should not be sprayed on reactive metal such as aluminum, tin, iron.
- Can irritate skin and trigger an allergic reaction; frequent exposure may cause chronic bronchitis, dermatitis and erosion of teeth.
Toxicity of Vinegar and Roundup
People like using vinegar because they think it is so much safer than commercial herbicides like Roundup. They are wrong.
Toxicity is measured as an LD50 value. The oral LD50 in rats for glyphosate, the active ingredient in Roundup, is 4320 mg/kg, which is less toxic than vinegar (3310 mg/kg). Low numbers are more toxic because it takes less to harm you.
Vinegar and Salt Killer Recipe
The vinegar + salt weed killer recipe consists of 1 cup table salt, 1 tablespoon dish soap and 1 gallon vinegar. Is this more effective than vinegar alone?
The soap helps the material stick to plants making it more effective. However soap also damages plants, which in this case might be a benefit.
Table salt is sodium chloride and the sodium is quite toxic to plants. It is the main reason this mixture kills plants but there is a big problem here. Salt persists in soil where it harms any kind of plant, including the good plants you are trying to grow. Eventually, water washes it deeper into the soil layer and eventually into rivers and lakes where it causes environmental problems. The EPA has this to say, “salt can contaminate drinking water, kill or endanger wildlife, increase soil erosion, and damage private and public property”.
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 sunlight 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 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.
Frequently Asked Questions
Q1? How long does it take vinegar to kill weeds?
Vinegar kills seedlings in 24 hours but it does not kill other weeds. It makes the leaves look brown in a few hours.
Q2? Is vinegar safe to use as a weed killer around pets and small children?
No! Vinegar can harm eyes and should be used away from pets and children. Horticultural vinegar is even more dangerous.
Q3? Will vinegar harm insects or other wildlife?
It can kill ants, spiders, mosquitos, amphibians and most insects. It is lethal to bees.
Q3? Will vinegar weed killer damage concrete, metal, wood, or other surfaces?
Vinegar is a weak acid but it can still damage wood, concrete and metal.
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.
I wanted to test vinegar’s ability to kill weeds for myself. I tried it on dandelions in Home Made Weed Killer – Roundup vs Vinegar vs Salt and on other weeds in Vinegar Weed Killer – My Experieince.
Ok I’m sorry but I think this post is incorrect. I have experimented for many months with both roundup, and other weed killers, and now a special mix of vinegar + soap and some secret additive (it’s safe). The vinegar has proven to be 10x more effective, AND permanently effective on my sidewalks, patio, and driveway. The roundup was partially effective but the weeds grew back. I haven’t waited 6+ months but as far as I’m concerned the vinegar is awesome. If it’s not killing roots – it’s dang well damaging the the heck out of those weeds.
Did you try to repeat my experiment – or a similar one showing your results? Lets see the results.
You are 100% correct. Spread the word, no reason to poison the world to kill a few weeds.
In the interest of full disclosure, do you have any ties, of any kind, to Monsanto? The only people I have seen in the past decade who have said that Roundup is environmentally friendly have been paid shills for Monsanto.
Many posts have accused me of being a Monsanto shill and I just delete them, but you asked nicely so you deserve an answer.
NO, I have no ties to Monsanto! I am a chemist who can read the scientific reports and understand them. The facts on glyphosate are very clear and well established.
If you have not seen anyone make the comments I do about Roundup you have not been looking very hard. Pop on over to The Garden Professors Facebook page and see what science says about the subject.
I never said “Roundup is environmentally friendly”. What I said was that it is a very safe chemical – safer than many chemicals you have in your home.
I’d like to kill my lawn and plant ground cover and meadow. I don’t want to poison my drinking water in my well. What shall I do?
Roundup – less toxic than vinegar.
Really, i can drink a cup of vinegar. Would you dare drink a cup of Roundup?
Yes really – you can easily check the facts on line. I would not drink a cup of either one.
Roundup is forbidden, or should be, around waterways. Do check the restrictions in your area (or your conscience). I live on the Chesapeake Watershed and participate in a community garden. Can’t use Roundup or any of the chemical (and completely effective) herbicides.
I make a slice down the middle of a dandelion about 6 inches down and expose the root. I poor some 20% vinegar in the hole directly on the root. Kills the dandelion within a day. Can also dig the top part of the dandelion out then pour the vinegar onto the bottom of the root. For other weeds embedded in the grass is use an organic approved Iron based chemical. Changes the ph of the weed without affecting the grass. Weed turns black in a few hours and dies within a day.
If you dig down beside the dandelion and dig up most of the root – it also dies with no acetic acid required.
The iron chemical you are talking about is probably Fiesta. It has been shown to be fairly ineffective; http://pesticidetruths.com/2011/10/31/fiesta-herbicide-dismal-failure/
Seems that if one goes to that trouble of “slicing down the middle of a dandelion about 6 inches down”,at that point of exposing the root why not just go ahead and pull the whole thing out of the ground?
Roundup is linked to TCC (bladder cancer) in pets. If you have dogs or cats in the area, I would advise doing a little research first.
Since it does not cause cancer in humans I doubt it will cause cancer in pets – where is your proof?
Well vinegar is an excellent annual weed killer , 10% really works good.
It works best on young weeds and wont hurt established plants if you over spray, yes perennial weeds will come back unless they are very young.and if used alot could raise the acidicy of the soil.
So Monsanto can kiss my tail
As you say 10% does not work on perennial weeds, or established weeds – sounds like a good weed killer to me!
Got sleepy reading this while searching for a natural way to kill weeds. I see no solution here and I am glad I didn’t go buy vinegar and salt. This could be a commercial for roundup though as much as its mentioned, Lol…
What do you recommend for killing grass/weeds in a large area to put in an above ground pool and deck surrounding the pool?
There is no need to kill the grass in either the pool area or desk area. Once covered it will die on its own. Many people want to remove the sod layer to get down to more stable soil – but again there is reason to kill the grass to do this.
For a garden, Roundup is one of the most environmentally friendly solutions. It is very effective at killing the grass, is very safe and does less hard to the soil than covering it with plastic.
I was wondering if 20% vinger would work on horsehair weeds and where i can find some in the uk or if theres any other solutions. Area surroubding it is slabs so no other plants nearby but its been growing there since 1940 when the house was first built and nothing has really worked. Any help would be appreciated.
Probably not. This is a very tough weed to kill. Use Roundup. Even with that you will probably have to spray a few times to get rid of it.
I’ve used muriatic on a small patch of ivy…put it on a couple of years ago and that patch of ivy hasn’t grown back. I also cut 3-4 inch thick ivy vines off several trees in my front yard, poured muriatic acid on the stumps and no new growth has occurred. The problem is that I can’t/won’t use muriatic acid on a larger scale (our entire backyard is covered with ivy) because we have a creek and deer live in the thicket next to our property.
I’ve been reading up on the vinegar/salt treatment but you’ve shot that down no matter what success other posters have had with it (short term or long term). For the reasons mentioned above, I am also hesitant use RoundUp or anything similar because I don’t want to harm the deer, our pets and the creek. Soooo…what can you suggest to kill the 2 foot deep covering of ivy that blankets the entire back yard? Hope you can help.
Muriatic is hydrochloric acid – I would not recommend that for weeds. It can be quite dangerous.
Roundup works well on ivy, and is quite safe for the environment.
Roundup is a probable carcinogen according to the WHO and is found in high residue concentrations in flour and other fruit and veg. It has been suggested that this will kill the bacteria in your gut when you eat food contaminated with it. Look it up online.
you read the WHO report incorrectly. Their first report said it is a ‘possible’ carcinogen. What does that mean? According to WHO it means they feel there has not been enough testing to determine carcinogenicity one way or the other. Some other things in the same category are things like shift work, being a hair dresser, and I think soda pop.
Since that report came out another report by WHO and the EPA says that they have reviewed more research and they are now convinced glyphosate is not carcinogenic.
Your statement “high residue concentrations in flour and other fruit and veg” is totally false.
Re “It has been suggested that this will kill the bacteria in your gut when you eat food”. The anti Roundup movement has main all kinds of suggestions. You can believe gossip or you can believe science.
I used to use round-up all the time until I heard all the hype on the news and read about it. I have switched to vinegar. The weeds come back within a few days. It is so difficult! I am, however very health conscious and don’t want to take any chances with the round-up! I garden as a hobby and have been using round-up for many years. My garden was always weed free; now I can’t keep up with the weeds. Wish there was something else safe and worked more effectively to keep the weeds away longer!
There is Glyphosate, ie Roundup. It is less toxic than vinegar – do you consider vinegar safe?