Garden Myths - Learn the truth about gardening

Homemade Weed Killer – Roundup vs Vinegar vs Salt

Homemade weed killers are all the rage and vinegar or salt or a combination of the two are highly publicized. How well do they work? How do they compare with Roundup? In today’s post I will compare the three options by testing them on real weeds in my garden.

Homemade weed killer - vinegar and salt

Homemade weed killer – vinegar and salt

Vinegar, Homemade Weed Killer

I’ve discussed vinegar before in Vinegar Weed Killer Myth. It is effective against small weed seedlings, and it does destroy the green leaves above ground. It has very little effect on roots.

In this post vinegar refers to the stuff you can buy in a grocery store. It does not include 20% acetic acid which is a dangerous chemical that does kill some weeds.

Salt, Homemade Weed Killer

Salt, usually in the form of sodium chloride, the table salt, is recommended quite a bit for killing weeds. It can be used in water, as a solid or even mixed with vinegar.

Salt does kill weeds, as well as all other plants. Sodium is a toxic metal ion which dissolves easily in water. It moves through soil along with the water. If the amount of sodium is high enough it kills plants, so it should be no surprise that it kills weeds.

Unlike synthetic or organic pesticides which break down over time, the sodium ion does not break down. It might be washed away by water to another location, like the soil where you grow favorite plants, or into local rivers and lakes, but it will always be somewhere.

Someone on a social network group said they kill weeds by applying salt, and nothing grows in the spot for at least 2 years. Great – the weeds are gone because the soil has been contaminated so much nothing will grow there until water leeches the excess sodium away. That does not sound like good gardening to me.

Roundup Weed Killer

The active ingredient in Roundup is a chemical called glyphosate. Contrary to popular belief, this is a safe chemical (ref 1) and it works very well on most plants.

Glyphosate is absorbed by the leaves of growing plants and is transported to the roots. There, it slowly kills the roots and in turn the whole plant dies. This process is fairly slow, and usually takes 10 – 14 days for the plant to die.

Roundup vs Vinegar vs Salt

The above descriptions are basic facts about the three weed killers. I wanted to see them in action and be able to compare them to see how effective they really are.

I know Roundup works since I have used it in the past on a few very stubborn weeds including quack grass and bindweed. I have never used vinegar or salt.

In early spring, I dug out some good sized dandelions and potted them up. I took good care of them for a couple of months to make sure they were growing well. The picture below shows the three plants just before being sprayed with a weed killer.

Homemade Weed Killer - Roundup vs Vinegar vs Salt 1

Homemade weed killer – Before being sprayed, June 22

Each pot was sprayed once with one of these: Roundup, pickling vinegar (7% acetic acid), and salt (1/4 cup sodium chloride per liter water).

After treatment, all three pots were added to my nursery of potted seedlings, which are watered every day unless it rains. They received sun most of the day, with a bit of shade late in the day.

Two weeks after spraying.

Homemade Weed Killer - Roundup vs Vinegar vs Salt 2

Homemade Weed Killer – Roundup vs Salt vs Vinegar, July 6

From experience, I know Roundup takes about 10 days to start showing results. Plants are usually dead at the 2 week mark. It looks like salt also did a good job and that was not unexpected. Salt, at high levels, is toxic to most plants. Vinegar had browned off the leaves a bit after spraying, but new ones soon grew back. The vinegar treated plant is smaller than before spraying, but is growing fine.

Eight Weeks After spraying

Homemade Weed Killer - Roundup vs Vinegar vs Salt 3

Homemade Weed Killer – Roundup vs Salt vs Vinegar, August 16

Does Salt Kill Weeds?

You can see from the above picture that the salt sprayed on the plant was not enough to kill it. Things might have been different if the plant had been in the ground. Salt is very soluble in water, and more watering means that it is washed away quicker. The plant would not have been watered as much if it was in the ground and so the salt might have stuck around longer, in turn killing the plant. But that is just a guess.

The salt treated plant is not nearly as large as the vinegar treated plant. So salt certainly affected the dandelion more than the vinegar spray.

Salt may be better at getting rid of weeds, but it is just not a good idea for treating weeds in the garden. Adding salt to your garden is not good for your plants or the environment.

Does Vinegar Kill Weeds?

The pickling vinegar did do some initial damage to the leaves, but it clearly did not kill the plant. This is consistent with scientific reports that say vinegar at 5% or 7% have very little effect on weeds that have well established root systems. See Vinegar Weed Killer Myth for more details.

Vinegar will not kill most weeds in the garden. 20% Acetic Acid does kill some weeds, but is not effective on all types.

In my next post I test vinegar’s ability to kill other types of weeds Vinegar Weed Killer Myth Revisited.

Will Vinegar + Salt Kill Weeds?

Some recipes recommend a mixture of both vinegar and salt. This is probably more effective than just vinegar alone, but again salt is just no good for the garden. I would not use it.

Many of you will have trouble believing me when I say Roundup is less damaging to the environment than salt. Roundup degrades fairly quickly as bacteria and is converted to water and CO2. Salt stays in the environment for ever.

references:

1) Glyphosate technical Fact Sheet: http://npic.orst.edu/factsheets/glyphotech.html

2) All photos by Robert Pavlis

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing 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.

89 Responses to 'Homemade Weed Killer – Roundup vs Vinegar vs Salt'

  1. Diana says:

    What about pets? I have dogs and a yard full of weeds. The dogs will be away from the house (we’re traveling for three weeks) so I was thinking of spraying Roundup before leaving. Will the ground/yard be safe after three weeks? I don’t them to accidentally get poisoned.

  2. Brian says:

    “The court documents included Monsanto’s internal emails and email traffic between the company and federal regulators. The records suggested that Monsanto had ghostwritten research that was later attributed to academics and indicated that a senior official at the Environmental Protection Agency had worked to quash a review of Roundup’s main ingredient, glyphosate, that was to have been conducted by the United States Department of Health and Human Services.”

    https://www.nytimes.com/2017/03/14/business/monsanto-roundup-safety-lawsuit.html?_r=0

  3. Ove Sorensen says:

    Your statement that roundup degrades after a short time is incorrect. Traces of roundup is being found in the drinking water here in Denmark. Our drinking water is pumped up from water wells 50 feet deap. How does the roundup travel so deep in the ground if it degrades shortly after??

    • Finding traces does not mean it does not degrade in a short period of time and I believe the reference was to glyphosate in soil, not water.

      Its half life is in the order of a couple of months – that is considered degradation in a short period of time. This value is well established.

  4. bdalzell says:

    I guess people these days are not aware of classical history, what the Romans did when the conquered Carthage. To destroy the civilization they plowed the fields with salt. No crops for many years.

    Good post. I have been able to kill poison ivy with repeated spraying of chlorox directly on the leaves without harming the nearby plants.

  5. Nicola says:

    I am looking for alternatives to chemicals to use on my weeds – and just to throw my 2 cents in on the vinegar/round up discussion I thought I would share my views. I eat vinegar so if some ended up on my good plants I would be happy to eat the vinegar (chemical or not), however I would not be happy to eat any amount of round-up. This is just simple commonsense to me and why I would not use RoundUp.

    However my question relates to using coconut oil as a weed deterrent. Down the side of my house I have a gravel path infested with all sorts of weeds (sigh) and I noticed outside my bedroom window a round circle of gravel with absolutely no weeds. When I do coconut pulling – I spit out the window (to prevent my drains from clogging) and where I do this there are no weeds. I think I last did coconut pulling over 6 weeks ago maybe longer. Could coconut oil be a good weed deterrent?

  6. Karl Zaker says:

    If possible, use BOILING WATER to kill off weeds (and anything else, including burrowing insects). Talk about easy! And no evasive? Lol. Works great, although not very practical, totally safe for my small children and pets- 100% DEAD VEGITATION.

    • Actually boiling water will not kill large weeds. What temperature do you think the water is once it reaches 6 inches below the soil surface?

      • Karl Zaker says:

        I suppose it depends on soil density doesn’t it. I used (don’t ask why) boiling water with vinigar. I didn’t thing it would kill everything off when I dumped a 15 gallon kettle on the edge of the yard but killed everything bare until this year (one season). I have some really large weeds that I’ll boils a turkey fryer full and dump it on them to see how well it will work on large weeds. I have used it on ants a few time and they burrow deep, worked flawlessly every time.

  7. Chica says:

    Thank you for pointing out that glyphosate is relatively harmless in the home garden. After avoiding any chemicals in my garden, I finally resorted to Roundup as one of several tools in battling goutweed, which I used after much research on its effects. From what I understand, it basically stays limited to only the plant you spray it on, and deteriorates afterwards, as you point out. I get “looks” from people when I say that I occasionally use Roundup on especially stubborn weeds. This is not to say, however, that excessive or near-harvest, commercial use by the farming industry on Round-up ready edible crops is safe, advisable or acceptable.

  8. Simon says:

    Very interesting topic.
    There is a Weedkiller being sold on a week known shopping channel that is Glyphosate free & uses some kind of extract ofGeranuim as an ingredient which also seems to kill the root as well and is biodegradable.
    I wondered if you’ve heard of this and have tested it at all?
    Thanks
    Simon

  9. Dan says:

    I was intrigued. Out of curiosity, can I use roundup on my asparagus after all the ferns die off without hurting the root crown. I have a friend that dilutes it and uses before the spears break the surface to control weeds. I want to spray at end of season then use a preemergent in spring.

    • Roundup is quickly absorbed by soil and will not penetrate very far into the soil layer, so it is unlikely to reach the asparagus.

      Secondly, glyphosate, the active ingredient works by being absorbed by leaves. If a plant has no leaves, it can’t absorb glyphosate very effectively. That is one reason it is recommended not to spray until a weed has grown enough leaves.

      • Cindi says:

        I just cleared my fence line and my neighbor has several invasive weed/shrubs whose limbs/branches have creeped under my fence. I don’t have a saw, hatchet, etc., just a hand pruning shear. If I spray Roundup on the cut surface where I was able to prune, will these die off. Or will I have to get a shovel and hatchet and dig them out of the ground? Many thanks. Renting a house and just don’t have the tools yet.

        • When you paint the cut end, the glyphosate will be taken to the roots where they kill the roots. So the whole plant dies.

          If you are cutting one branch of a shrub, it is not likely to get enough chemical to kill it.

  10. richard bowers says:

    what if you use a propane farmer type weed burner for cracks in sidewalks and driveways? Is that temporary? I have always found it is the seeds that seem to sprout, after killing with roundup. Is this a true observation?
    thank you,

    • A torch kills off the tops of the plant – it does not kill the roots.

      Roundup has no effect on seed, so it should be no surprise to see seedlings after treatment with it. But that is true of most things people use to get rid of weeds.

  11. Certainly didn’t expect the comments to be so heated, but damn if they aren’t entertaining! I’ve done the vinegar/salt/soap mix for years, using it every couple weeks on the same spots because yes, it just kills the tops. I’ve used Roundup in the past and there’s just no comparison. (I’m not a shill for Monsanto, though if I was I’d probably deny it…) Having said that, I opt for the vinegar mix because I can mix it up in the kitchen with my toddler underfoot, I don’t have to wear gloves or freak put if it back-sprays on me, I can have said toddler and cats running around the rocks as I spray it, and we’re outside all the freaking time anyway. When my situation changes, I might switch it up, but the vinegar is actually easier for me – despite the frequency – as a stay-at-home mom.

  12. GKnotek says:

    I am wondering if repeated removal of the surface vegetation of a weed – by hand or with vinegar – will eventually cause the root to die. I will be grateful for any insights. Thank you.

    • Yes this will work – provided that new growth is removed before the plant can make more food than it lost growing the new leaf. Weekly removal should work for most plants – but miss a couple of weeks and you are back to square one.

    • rdtrainer says:

      I’m kind of surprised at your insistence that glyphosate has been scientifically proven to be safe. That leads me to believe you are either a spokesman for Monsanto (are you?), or you aren’t familiar with all the literature.

      There are, for instance, many peer reviewed papers on the subject by MIT researcher Stephanie Sennef. The following is how Dr Sennef is described on her site.

      • I’ve edited the rest of your comment, because the work of Stephanie Sennef has been completely debunked as being poor science. Her work is not accepted by main stream science.

    • Victor Cicconi says:

      I do have a question, If salt makes it so plants won’t grow for up to a year or more. How come they use it on the roads, and the sides of the roads are full of weeds every summer..

  13. JIm Friden says:

    I would like to comment after reading your Aug. 26th 2016 post about organic food (plants) that are “naturally resistant” to pests. This by the respected physicists at Cal Berkeley Richard A Muller who says in his book The Instant Physicist this: “Typically, the natural pesticides in organic food are thousands of times more carcinogenic then the artificial pesticides approved by the U.S. Department of Agriculture. And since they are part of the food, they can not be rinsed off”.

    Thought your readers would like to know this.

    • the statement “natural pesticides in organic food are thousands of times more carcinogenic then the artificial pesticides approved by the U.S. Department of Agriculture” is simply not correct.

      1) natural pesticides occur in both organic and non-organic food – there is no evidence that those in organic are any worse or better than non-organic.

      2) Plants make thousands of natural pesticides. There are hundreds of synthetic ones. Any blanket statement that says one group is more carcinogenic than the other group is not only incorrect – but its a stupid statement. Each chemical needs to assessed on its own merits. Besides, most of the natural pesticides are still being studied – we don’t even know what they all are, let alone how they affect animal cells.

  14. Kat says:

    This is a website for normal people at home who need advice on killing weeds, not a science lab or college study. Give the man a break! I found this site because I was going to try to save some cash and use the vinegar. Thanks to this article I know to just go ahead and get the round up. I’m sure your comments are appreciated, but they are really long winded and boring for someone trying to have a nice yard. Thanks for the advice and unfortunately I’m sure there are some 8th graders failing science because their teachers were to busy on here trying to sound smart rather than working…😁

  15. Steve says:

    I read this entire thread with interest, although I am late to the party. Just because the WHO, or the EPA say that RoundUp is non cancerous, I for one doubt their sincerity. After all, both of these agencies fir in the “Big Govt, Big Business ” country club. They all scratch each others backs. I just dont buy it, or their test results.

  16. joejoe says:

    Hello, really enjoyed your gardening experiment and all the comments..

    I too have tried and failed to kill weeds with typical white vinegar 5% acetic acid… So I decided to try Muriatic (i.e. Hydrochloric acid) acid from my pool supplies, full strength on a few weeds on my rocky walkway beside my house….. Not to worry.. Muriatic acid will react with all the limestone and river rock and not linger in the soil. However it is a much stronger acid than vinegar

    At first it appeared that the muriatic acid did the trick, as it burned all the organic material… However within a month or so, the weeds returned.

    My conclusion is that using acid does not kill the roots of weeds or invasive plants..

    I am interested in any homemade mix that is effective and less toxic than Roundup.. Yet to see one.

  17. Jeffrey Myers says:

    Hi Robert,thanks for the info.I did not see it mentioned in your article.My question is did you use a surfactant (like dishwashing liquid) with the vinegar spray or the salt spray?,that would make the vinegar or salt “stick” to the weed longer.

  18. Boiling water kills weeds, too, and is cheap.

  19. Laplander says:

    There are various theories as to why Sodium Chloride kills, but the toxicity of Sodium is not one of them. Toxicity has been identified as the increase in cellular levels of chloride, the displacement of other cations in the soil by sodium, and by lowering the availability of water and thereby dehydrating plants, or through hypertonicity which will cause cells to shrivel as water is drawn out of a cell All cells have very active sodium pumps that keep sodium levels low within the cell. Even salt tolerant archaea survive by pumping sodium out, and so it is unlikely that any toxic effect can be exerted in an otherwise healthy cell. Moreover Sodium is ubiquitous in the environment and an indispensable component of living systems. Sodium ion is not “washed away,” but is highly soluble in water and will diffuse through the environment, especially if you are watering your plants. “Washing away” is what happens to particulates, and sodium chloride is not a particulate when dissolved in water. When the concentration drops below highly concentrated levels, it won’t affect anything. You have made it sound like Sodium is a toxic metal which stays around doing damage. Far from it. Remove all sodium from an environment and nothing will survive.

    You have also tested common vinegar which is not recommended as an herbicide by any source I have seen. The 20% form is recommended as an herbicide. The precautions would be similar to that used for Roundup. Moreover, if you do get some on you, just hit it with water and it will dilute down to vinegar strength quickly. Wear eye protection and long sleeves. It is no big deal.

    You approach to addressing the concerns about Roundup typically involve ad hominem attacks against authorship which makes you sound like a virulent Roundup salesman. Monsanto sues people who grow crops using their seeds without paying royalties. The one case in which pollen was implicated was a lawsuit in the other direction – the farmer sued Monsanto for contaminating his crops, but failed to prove it. The commercial use of glyphosate lessens the overall application of herbicides to crops. In addition, there are overall economic benefits to farmers who use it. If you are not an organic farmer, it seems to be the way to go. However, is it necessary in a home garden? And your blithe dismissal of its suspected carcinogenicity is disingenuous. Having worked in chemical carcinogenesis research and watched its progress over decades, I will say this. Synthetic organic compounds, that are not natural products, are suspect from the start. If they are identified as a suspected carcinogen, that usually means they have a chemical structure similar to known carcinogens, and there is not enough data to address the hypothesis. Using Roundup on a garden exposes someone to such a compound, unnecessarily. When the data come back in twenty years, and there is or is not a statistical correlation, ask yourself if you want to be one of the test bunnies for Monsanto.

    Organic farming is labor intensive and there is little evidence that it produces safer or more nutritious food, The produce is more expensive. Yet I buy it whenever I can, because I reject the assertion that increasing efficiency in the mass production of food has created a better world. It has collapsed the economic base of farming and concentrated control of it into the hands of a very few. It has created a world where food is so cheap it is wasted, and makes the soil and water sewers for every new experiment that comes down the pike. The GMO that increasingly dominates our crops is creating a monoculture world dependent on corporate control. The current state of affairs will also not last, as Roundup resistant weeds are being selected for and that will create a spiraling competition with natural selection that people will lose. And because some apocalyptic genetic accident has not yet occurred, there is clear evidence of the escape of these modified genes into the wild, and we are merely waiting for the extinction of some species because we want cheap popcorn or cotton T-shirts. In other words, 20% acetic acid, saturate it with table salt, and a few drops of dish soap and you will likely have something just as effective as roundup. And you can use it long after Monsanto goes belly up like Johns Mansville did for asbestos.

    • Keep in mind that this website is targeted to gardeners and not chemists. The actual mechanism of sodium toxicity is not that important, and maybe the term is used incorrectly, but it is the term best understood by the gardening community. also, even the scientific community uses the term, as for example in “Uptake of ubiquitous sodium ions is desirable as a way to build osmotic potential, absorb water and sustain turgor, but excess sodium ions may be toxic” in http://www.ncbi.nlm.nih.gov/pmc/articles/PMC139373/

      The reason for discussing common vinegar instead of horticultural vinegar is that the majority of gardeners using acetic acid are using common vinegar. I never said ti was recommended as a herbicide – but it is what is being used and what is being constantly promoted in social media.

      When WHO. The world health organization looked for evidence that glyphosate causes cancer they found none and labeled it as ‘possible cancer causing’. They looked at 50 years of testing. In the past year they have now stated that it does not cause cancer.

      • ’16. After being regularly exposed to Roundup, two men who used Roundup for yrs have both developed non-Hodgkin lymphoma, a blood cancer that starts in the lymph cells. Both are plaintiffs in a suit filed against Monsanto that marks a turning point in the pitched battle over the most widely used agricultural chemical in history.

        Until recently, the fight over Roundup has mostly focused on its active ingredient, glyphosate. But mounting evidence, including one study published in February, shows it’s not only glyphosate that’s dangerous, but also chemicals listed as “inert ingredients” in some formulations of Roundup and other glyphosate-based weed killers. Though they have been in herbicides — and our environment — for decades, these chemicals have evaded scientific scrutiny and regulation in large part because the companies that make and use them have concealed their identity as trade secrets.

        Now, as environmental scientists have begun to puzzle out the mysterious chemicals sold along with glyphosate, evidence that these so-called inert ingredients are harmful has begun to hit U.S. courts.
        So you see it’s not just glyphosate as you have failed to mention.
        Roundup and Monsanto soon to be owned by Bayer are true detriments to safely and optimally grow agriculture. And since organic foods don’t have these from the get go toxins in them even though their nutritional value “may” be equal, makes them obviously less desirable.

        • The EPA and the World Health Organization have now both determined that there is no scientific evidence that Roundup causes any form of cancer. Just because someone is suing Monsanto proves nothing.

          It is true the ‘inert ingredients’ have been studied less, but most cancer studies in field conditions used the whole Roundup product, not just glyphosate.

          Organic food may not have these chemicals, but they contain lots of other natural pesticides. In fact in North America we eat up to 1,500 mg per day of these pesticides. http://www.gardenmyths.com/natural-pesticides/ Since we know almost nothing about these chemicals I would wory about them more.

          • Rodney Merrill says:

            For about 50 years, there was no proof that smoking caused cancer and a host of other diseases; but that’s because the tobacco industry spent billions of dollars burying evidence and buying scientists to falsify results. They finally were found out but for decades we heard there was no evidence. My money says the same thing is true of Roundup.

            I am disturbed by your glib attitude about something being poured into the environment by the megaton.

          • It is not my “glib attitude”. I am simply reporting on information approved and verified by just about every organization including the EPA and the World Health Organization.

            When people first starting smoking we did not know about the hazards – that was over 100 years ago. Science had proof about the hazards more than 50 ago – people just did not believe the scientists – they preferred to keep smoking.

            What people seem to forget is that the herbicides that proceeded Roundup were much more toxic. Sure it would be better not to use any herbicides – but people won’t pay for that option – food prices would skyrocket.

          • Barbara says:

            I have to jump in, I can’t stand it. You are clearly pushing roundup as the safest way to go for killing weeds and it’s not toxic. I could care less about your research and trials that it does not cause cancer. Try talking to real people. I used roundup as a landscaper both at work and at home. It kills beneficial insects and I have advanced stage kidney cancer. I had dogs die of cancer. As far as using salt, vinager, and dawn it works!!!! I don’t spray it all over the property, I use it in areas where there is no need for weeds or plants and where my dogs go out to lay in the sun or do their business. I HATE roundup. You also mention that you spray it directly on the plant, we know that, but this gets very costly as other weeds pop up next to in in just a few days. AND for those of us that are getting too old to pull weeds every stinking day and have pets as our only companions…NO WAY IM GOING TO POISON MYSELF OR MY DOGS!

          • You are free to believe what you want – no one forces you to believe in science. But just because you believe – does not make it fact.

    • Ari says:

      Non-organic/GMO agriculture is responsible for feeding millions of third world people all over the world. But feel free to feel good about yourself along with other wealthy enlightened “Whole Foods” consumers who won’t have to worry about starvation and other problems caused by poverty

  20. One ‘weed’ I have very quickly killed with ordinary vinegar is a primitive horror called ‘liverwort’ (Marchantia polymorpha).

    It grows like melted green wax on the ground in areas where the soil is moist and fertile and the air, humid.

    Killing existing liverwort is only part of the solution however because it will grow back from spores if the underlying conditions for its existence are not altered.

    PS I have really enjoyed reading the comments to this post.

  21. Carol says:

    I appreciate your test of vinegar. I am planning to try my own comparison on a gravel walk.I agree that Round-up works well in killing weed roots and has not been ruled a human carcinogen. But is inhaling Round-up safe? No, I am not ignoring directions. I live right next to a 50+ acre soybean/corn field that uses it generously at least 3 times a year. Even when the applicator is spraying on a still day (not that often) I smell it in the air for hours. I was told by an Ag Dept. rep that it can volatilize and drift up to a mile in hot still air.

    • You have to breath in a lot of Roundup before it would do any damage.

      The perfume people wear is probably more harmful, and your morning cup of coffee is definitely more harmful.

  22. Scott ritchie says:

    I want to play it safe for now, I’m trying to avoid using round up when possible. But if the job calls for it I will use it, we know it works very well. What do you think of using a weed torch. My plan this year is to use the weed torch in and around the garden. Will it work.

    • I have not looked at the weed torch in detail, but I suspect it has the same problem as vinegar. It burns the top green leaves and the root remains. I don’t see how it could possible damage a dandelion root that is 6 inches deep in the soil.

  23. tom young says:

    GREAT, I wish everyone would realize that any article needs to be researched and not just deemed true because it’s in print.

  24. Mark says:

    I am curious as to whether the 2.5 pH acid water produced by my batch-type water ionizer would be effective in killing the weeds that grow between the bricks and pavers on my patio.

    • I doubt it. If the low pH damages the leaves, they no longer work properly, and the root is saved. Herbicides work because they don’t damage the leaves. The herbicide is absorbed and spread through out the plant, and then chemical reactions kill the plant.

  25. Eloise Eccles says:

    From a chemical engineer, gardener, and drinking water contaminant expert – – I truly appreciate your logical science based assessment of chemical weed-killing products. Garden on! And keep up the great research and communication. On the subject of salt, I am very concerned about the long term impact of roadway and walkway de-icing chemicals.

  26. A lot of the recipes on the internet for homebrew herbicides specify epsom salt rather than salt. Can you say anything about its usefulness or dangers?

    • Epsom salts is even more useless than either vinegar or table salt. All this product does is add magnesium and sulfur to the soil. Most soil does not need more magnesium. It is also recommended as a tonic to be sprayed on plants. Can’t be both a tonic and weed killer! Epsom Salts for plants

  27. Paula Beattie says:

    This is a good experiment, however; I would also like to see something else planted in the pots directly after the experiment concluded after 8 weeks time to see how it fares. According to your comments, salt would prevent another plant from growing, as well as the weeds. Next year, I will try this experiment but do it in the ground to see if there are residual effects from the salt.

    • Trying other plants after using salt would be an interesting experiment. I was quite sure the salt would kill the dandelion but it didn’t. I suspect that in pots which are watered a lot, the salt is washed away, and that explains why the dandelion came back.

      When I moved into my home, the water softener was emptying into a sump, and then pumped into the woods next to the house. This water would have contained a lot of salts including sodium, calcium, and magnesium. The ground was actually white with crusted salt. Nothing grew there.

      • Lets start by analyzing the credibility of the authors. It is an organization called ‘Institute of Science in Society’. Who are they? A qwuick Google and you learn all kinds of stuff. In addition to being anti-Rounup, they are also anti-GMO and pro-homeopathy. The director and principal author is Dr Mae-Wan Ho. From Wiki, “Ho has been criticized for embracing pseudoscience” – that does not sound good.

        80% of the worlds scientists see no health risks with GMO plants. Ho is not part of the majority.

        There is no creditable scientific evidence for homeopothy – Ho believes it to be valid.

        I see no credibility in the organization or with Dr. Ho. Today, on the web, it is easy to find junk science articles and reports to prove any point of view. If you want to truly understand the facts, read creditable material, and participate in science based discussion groups. for gardeners, the Facebook group called Garden Professors is one of the best.

        By the way, I also don’t trust websites that have been formed in order to sell stuff – Dr. Ho uses the Institute of Science in Society to sell her books – is that a conflict of interest?

        • For 10 years it was widely accepted by MOST scientists that humans possessed 48 chromosomes. It didn’t make them right.

          • True that in the early 1900 we thought there were 48. but remember that was at a time when DNA studies were very new. Chromosome studies was a frontier. Science is a self correcting system that over time gets to the right answer.

            The facts in this post are not new and are not at the frontier of science. Roundup has been studied for over 50 years. We can be reasonable certain that we a good understanding of it. That does not mean we know everything, or that some of our info might be wrong, but as time goes by it becomes less likely to be the case.

    • When looking at any report, the first thing to do is check for credibility. This article is written by GMwatch. Who is GMwatch? The managing editor is Claire Robinson who is founding editor of GMOSeralini — a website promoting the research of French scientist Gilles-Erich Seralini. Seralini is an unreliable, discredited scientist who has been forced to retract some of his research. So the author and article has no credibility.

      This point is real simple. It is very easy to find junk science on the internet to support any position.

      But lets look at the data presented. Much of it is rubbish, but the statement “the World Health Organisation’s cancer agency IARC decided that the herbicide is a “probable” carcinogen”, is worth a look. After all WHO and IARC are creditable.

      The quoted statement is only partially correct. IARC made no decision about Roundup as suggested in the title of the article. The classification was for glyphosate, the active ingredient in Roundup. The classification of 2a, ‘probably a carcinogen’ is correct. This should serious, but is it? In order to understand ho0w serious this is you need to understand what IARC is saying. IARC says gyphosate is probably a human carcinogen, but they are not saying that normal exposure will cause cancer. On the surface these sound like the same things – but they are very different.

      The reason it is considered to be a probable carcinogen is because there is not sufficient evidence to suggest it ‘is’ a carcinogen.

      To reach their determination, IARC did NOT take into account the exposure levels people experience. It is critical to take into account the exposure levels in order to reach any risk assessment for glyphosate. The dose is what makes the poison.

      To better understand this have a look at this video:

      To put this into perspective, IARC has also classified the following as ‘probably causing cancer’:
      – nitrate – would include most fertilizers you might use
      – sun
      – fried food
      – burning weed – ie campfire
      – job as a hairdresser or barber
      – doing shiftwork
      – gasoline
      – pickled vegetables

      All of these items are also probably causing cancer like glyphosate. We are not very concerned about these items because of dose. Same goes for glyphosate.

  28. Tony Reinhart says:

    Before you decided to declare Roundup safe in this post, did you consider any of the science around its effects on humans? It isn’t just about glyphosate, but about how all the ingredients within Roundup interact, including those labelled “inert.” This piece from Scientific American explains it well: http://www.scientificamerican.com/article/weed-whacking-herbicide-p/ If your goal is to provide reliable gardening advice, don’t you owe it to readers to acknowledge the science before concluding that Roundup is safe?

    • Of course I considered the effects on humans – how else can one conclude a chemical is safe?

      I am always amazed how people select the ‘truths’ they believe. For the moment, lets assume that the facts in your reference are correct – they are not – but lets assume they are. Scientific American would not lie, and the author is fully versed in the subject and has read over much of the original studies to understand the issues – right?. The article presents two main points of view:

      1) After 35 years, and hundreds (more like thousands) of research studies, the EPA and the U.S. Department of Agriculture consider Roundup to be safe.

      2) One research paper by Gilles-Eric Seralini finds Roundup is ‘deadly to human cells’.

      Why would anyone suddenly believe Roundup is not safe given these two facts?? Science is an iterative process and new findings need to be verified before they are taken seriously. One study means nothing.

      Now lets look at some facts:

      1) Gilles-Eric Seralini is one of the most discredited researchers I have ever read about. Over the last 10 years or so he has published several articles that the scientific community does not take seriously. He is the one who published the pictures of rats with huge tumors after they ate GMO grain. Most people believe he faked the results, in part because he refused to release his data – something that is unacceptable in the scientific community. Seralini has also retracted at least one of his research papers due to poor design and multiple errors.

      2) His work in the mentioned research paper was on single human cells. His findings tell us nothing about how Roundup affects a total animal. You can not reach the conclusions mentioned in the Scientific American article based on his experiments on single cells. That is not just my opinion, but that of the majority of scientists that reviewed his work. By the why, I also used similar types of human cells in my research on carcinogens – so I know a little of what I am talking about.

      The only part of the referenced article that is correct is that POEA is more toxic than glyphosate. You can get more details here, https://en.wikipedia.org/wiki/Polyethoxylated_tallow_amine POEA is not a toxic chemical.

      Here is a review from PubMed http://www.ncbi.nlm.nih.gov/pubmed/10854122 which concludes “Roundup herbicide (including POEA) does not pose a health risk to humans.”

  29. Roy says:

    Thanks again for an informative article . . .

  30. Rae Wade says:

    Robert: Monsanto’s Ag-giant production of GMO crops and its subsequent suing of neighboring farmers who save their seed, some of which may contain pollen from GMO fields, along with its Agent Orange history, has given it the reputation of a slimeball company. Nevertheless, its RoundUp is the only weedkiller that I find is really effective, other than expensive pre-emergents which I have to apply three times a year down here in GA. Now to my question: I have a stream flowing through my property which at different times of the year has tadpoles, frogs and an occasional snake. RoundUp warns against using the product near streams. Do you have any reliable information as to how to define “near?” Can those dying roots send the product into the stream banks? I’m talking poison ivy, kudzu, greenbriar and pokewood.

    • I won’t defend Monsanto, but most of what you read is baloney! Monsanto has not sued farmers who save seed that has some GMO pollen in it. That is a story being perpetuated by the anti-GMO movement. Just think about it – if they could win such a case, every farmer that grows seed next to a GMO farm can be sued. This makes no sense. The farmers they have sued have all signed contracts with Monsanto to use their product and stick to certain guidelines.

      I think that very little glyphosate would leach out of roots that have been treated. It is going to remain inside the roots until they are decomposed by microbes which will decompose the glyphosate molecules at the same time as the roots. The bigger problem is wind carrying the spray into the water when you spray. To a lesser extent, glyphosate that ends up on the soil can also leach into the stream with subsequent rains, but this movement is very slow as most soils hold the molecule quite tightly.

      If you make sure there is no over spray getting to the stream you should be good.

    • Art Thompson says:

      I recommend Crossbow for the plants you’re trying to kill. I have not researched the ramifications of using it near water, other than the boilerplate ‘It is toxic to fish’ verbage.
      I’m a big fan of Diquat. It is not harmful to aquatic animals and is therefore specified for aquatic use. I mix small amounts with my Glyphosphate to create short term ‘burndown.’ That way I can tell by the next day what I missed in my spraying.

    • Kyle Peavy says:

      I also despise Monsanto and their bs — but, I’ve been using the concentrated Round-Up on greenbriar fairly successfully. I apply it with a q-tip directly to the leaves. It seems most effective on the newest, softest, leaves. With repeated treatments (2x/month during the growing season) I’ve gotten rid of 80% of the greenbriar around the perimeter of my yard in one year. My q-tip application should go much faster this year than last year 🙂

      • Roundup is most effective when the plant is well growing. when properly applied it will not affect the leaves until the roots are destroyed which takes about 10 days. Concentrated product can be too strong and damage the leaves before the glyphosate is absorbed into the roots.

  31. Anne says:

    You make a lot of sense. Thanks for conducting the experiments, which I love reading about, and validating that Roundup is the best alternative to hand-weeding.

    • I never said “Roundup is the best alternative to hand-weeding”. In fact I hand weed almost all my weeds – I think it is a better option in most situations. Don’t use chemicals – of any type if you don’t need to. I just don’t use vinegar since it does not work – and that is also a chemical.

      There are some situations where Roundup is a better option. You can’t get rid of European buckthorn, or bind weed by hand pulling.

      The best defense for weeds is mulch.

      • Chris Tory says:

        BEST THING FOR WEED IS THE PUll them out… Fashion way !! Just pull the weeds out by hands AMEN..

  32. hotwired64 says:

    I’m more concerned with soil persistence and “carry-over” to future crops. Roundup has an active persistence of about one month, compared to months for vinegar and years for salt. Carry-over persistence can increase significantly in high clay content soils. Roundup has a very bad reputation. Some of it is deserved, though not necessarily by the chemistry, but by Monsanto’s actions and behavior. For this reason I wouldn’t use Roundup, but a great post.

    • Persistence is an important criteria for evaluating chemicals. Acetate (vinegar) will be used very quickly by bacteria. A persistence of 1 month for a chemical is considered to be very short. For Roundup it can by several months depending on soil type – but even that is considered short.

      Another criteria is how the chemical reacts with soil. It turns out that Roundup binds fairly tightly to soil. That means the carry over to other plants is very small.

      It is certainly true that much of the bad reputation for Roundup is due to a dislike for Monsanto – but I think that is just dumb. If people don’t like Monsanto, then they should stop using their products because they don’t like the company, and give that as the reason. But a lot of people make up untrue stories about the product in order to dislike Monsanto – and that is wrong.

      • Yusuf says:

        Hi following from this, I am looking for something affordable that I can use thats persists for a Long time. I read in another thread that salt is one. I would like to poison the soil under my tar to prevent constant grass coming thru small invisible holes.

  33. rogerbrook says:

    it’s surprising what a gardener can do with just a few simple experiments.
    Excellent authoritative reference on glyphosate. I have book marked it for future use!

Please let me know what you think - Leave a Reply