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.
I have successfully killed weeds by FIRST mowing them as short as possible and then POURING the vinegar on them. Spraying the leaves is just spitting in the wind. ‘;D
I doubt that is true. Vinegar is a contact herbicide. If you remove leaves, and then spray – there is nothing to contact.
Now that may depend on your definition of “pouring” – how much you pour on each plant, and the pH of your soil.
Wow,
The amount of stupid in some of these comments is appalling and I commend this website for a level-headed post on this topic. Even 20% Acetic acid is potentially very dangerous for a layperson to handle, is not going to kill most tough weeds at all, and it’s ludicrous that anyone would pass it off as a substitute for correctly-applied glyphosate.
Fortunately the recent absurd lawsuits in the US will be reversed on appeal and the ambulance chaser segment of our society can move onto something else to whip the weak-minded into a hysterical frenzy. No, I wouldn’t drink the stuff and Monsanto should never have tried to say it was ‘no more harmful than table salt’ (although it is probably less acutely toxic) – BUT, it has been safety tested more than almost any chemical used in the consumer segment and trust me, it’s no more dangerous than about 50 other things found in one’s home. There’s actually far more convincing scientific evidence connecting red meat and fast food consumption to cancer – yet do we see juries giving people $250 million settlements for eating McD hamburgers?
Aspartame and other substitute un-natural crap has been around 50 years. They just now finding it kills off the good pro and pre biotcs that your gut needs to be healthy. Even common table sugar is not natural as most thought!
Just because they all look the other way don’t make it safe! Other countries have good reason to ban certain products that is accepted in the U.S. It about the $$
It is more about political pressures than any science.
20% vinegar also kills the helpful microbes in the soil. It will also change the Ph of your soil making it more acidic. This was confirmed when I asked the manufacturer if that was true. So, it may or may not kill the weeds but it will harm your soil making it hard to grow flowers, shrubs, trees and grass. That’s not a good benefit/risk ratio if you ask me.
“This was confirmed when I asked the manufacturer if that was true”. I am not sure that is a confirmation – depends on the knowledge of the person you asked.
20% vinegar can harm microbes – but the effect would be short term in the spot you spray.
Unless you spray a lot – it will not change soil pH – which is very hard to change.
Acetic acid is also microbe food – so it is quickly eaten up by microbes.
I have a flowerbed in my front yard that has grass growing in it from a lawn that is less than 3 feet away I think. (The flowerbed has a sidewalk in front of it). The past 2 years we have had SO much grass growing in it that besides yanking it out by hand we have not had any success stopping it’s spread. It is so bad now that we cannot grow anything in the flowerbed as it all dies as the grass takes over. Please PLEASE tell me what I can do to get rid of this grass permanently. We have successfully grown marigolds and petunias in this garden and now nothing grows there. The soil is very dry now too for some reason. A nearby flowerbed appears to have a weed like plant resembling a tiny leafed nasturtium but it has no real flowers. This also cannot be controlled. What can I use to get my beautiful flowerbeds back? My front yard is looking like a derelict abandoned area.
Step one is to identify the grass. Different grasses grow differently and are controlled differently. Join a Facebook gardening group and ask them for help.
Hi. Grass spreads by root bits being left behind. Perhaps you might consider smothering them. Newspaper an cardboard work remarkably well – when applied thick enough – then cover with a good organic mulch. In the spots you wish to plant you’ll need to dig a hole at lease twice a big as your root ball an be very careful to remove every bit of the grass roots. Be sure to stir in some compost with the remaining soil, so your new plants will have nutrients to live on – and attract worms to the party.
Good Luck. Don’t give up, just dig a little deeper.
Ortho Grass-B-Gone will kill grass and won’t harm your other plants. It kills GRASS ONLY!
Hi, I started using Acetic Acid this year to kill our over abundant Blackberries. I use the 30% solution and the one thing I do differently than anyone else I have seen post is I add dishwashing soap to my sprayer. It makes the spray stick to the plants and I am having great success with it. Two other things. Spray first thing right after dawn if you can so the plant sucks up the moisture on the leaves and second. This process works much better later in the summer vs spring or early summer. You want the plants you are trying to kill on the downward side of their lifecylcle so they can not take nutrients back to the roots. This has worked great for us.
Do not use 30% acetic acid unless you have been trained in the use of hazardous chemicals. It can cause serious harm.
First I am a chemist by profession. Second, vinegar is a weak organic acid. Third, vinegar burns the entire weed down. Enough said.
I have a black locust overtaking the yard since the tree was cut early spring and the lawn mower died. I have a hydrangea nearby and don’t want to disrupt it. I will if I have to. Someone recommended crossbow. It says it is non-selective but then I read it will not kill grasses. Is that just because it only kills woody plants?
Someone told me I have to check with my extension in my County to see if Crossbow is okay to use. ?? I haven’t read up on it yet but wonder if there are any health concerns. I have pets.
I have some blackberries I could probably kill off as well. I will wait until after the season. I have loppers. I usually let everything grow naturally and not care too much as long as it doesn’t turn into a fire hazard.
Since you know the science behind the glysophate in Roundup and know it will kill these plants ok, I’m wondering about the other ramifications though. What about for the bees?
Thank you for the info,
Penny
Cut the woodies, and paint the cut stem within 20 minutes of cutting. It gets absorbed into the roots and kills the plant. It will not harm any insect unless they come and lick the Roundup before it dries – only takes a few minutes.
This is very effective and uses very small amounts of chemicals.
I am coming to this post looking for alternatives to killing Woody plants. I also have a question or two for you. Someone said if you put the vinegar down into the woody base, by drilling a hole that it would help get to their roots.
It won’t let me post all of it without hiding the post comment submit button. So look for my second one please. Probably cuz I’m on my phone.
Vinegar is a contact herbicide – I doubt it does anything in a hole drilled in a trunk.
Quite a discussion. I have used roundup and vinegar and hot water.
The Roundup was only tempory as the weeds died but came back , just as with vinegar. I killed some weeds with vinegar spray a few weeks ago and now I see grass growing instead. The weeds all came back after a month or two with the roundup but no grass even thought we eventually tried to seed it.. Hot water seems to do the job for a. season or two on walks but more they or their relatives eventually come back.. I would love to use hot water extensively but it is impractical. We have very poor soil which readily grows many weeds. I can’t physically attack them all with hot water.
National Geographic had an article in 2015 about Roundup entitled
” What Do We Really Know About Roundup”. Interesting reading. Also, it seems that Roundup Ready seeds, another Monsanto product, have contributed to other problems including what the Dept. of Agriculture
refers to as super weeds , a need for stronger Roundup, and the loss of several family farms. You can do a little research on these subjects.
I come from a farm family, I have relatives that swear by chemicals I would rather not have in the foods chain. There is no convincing them.
Very few weeds do not come back after being treated with Roundup – provided they are treated correctly. There are some tough plants that can live through a Roundup treatment. What you are seeing is new seeds germinating.
Roundup ready seeds are not creating super weeds – they were starting to show up before the seeds were used.
The Romans used salt of some sort so the story goes.
I do not trust this “scientist.” I think that he doth protest too much! I will go with the natural route.
But vinegar is not natural – it is a man-made chemical.
Vinegar is very natural. You, as a chemist, are very very very very very well aware of that. Why you are trying to promote a facial false narrative is beyond me.
Alcohol is a natural substance produced by yeast eating plant sugar; alcohol that oxidizes turns into ascetic acid – vinegar. The only thing unnatural about it is the deliberate manufacture of alcohol in greater than trace amounts, which then allows its oxidation into ascetic acid in greater than trace amounts.
For what it’s worth, the family of pyrethrin insecticides is also natural, being a compound found in chrysanthemums. The only unnatural thing about it is concentrating it for use on plants other than mums.
With your definition of ‘natural’, the vitamin C chewables for cold remedies are unnatural.
Good grief.
I don,t understand your point.
Vinegar exists in nature, but a bootle of concentrated vinegar is not natural.
But the point of the post has nothing to do with this – does not kill weeds.
I am looking for a large scale solution to kill leafy spurge on pastures and hayfields in North Dakota. There are many chemicals that have been tried and some are effective however we are losing the battle to this invasive weed. I am looking at the 30% vinegar as a possible solution. We are talking acres of leafy spurge. Any ideas or experience with vinegar on spurge? Thank you.
Use a real herbicide.
Hi, Master Colorado. I tried the link #2 to Vinegar as a burn pesticide and it goes to a dead end at USDA. Do have a better link or a copy of what was there? I have this discussion all the time and I’m trying to find handouts. Thanks.