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.
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.
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.
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
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
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.
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
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.
http://www.globalresearch.ca/monsantos-roundup-glyphosate-narrowly-missed-being-classed-as-known-human-carcinogen/5469093
Also read this http://www.i-sis.org.uk/Banishing_Glyphosate.pdf
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:https://www.youtube.com/watch?v=CbBkB81ySxQ&noredirect=1
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.
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.”
Its strange how we can accept anything that is toxic. A clean knife is less toxic than a dirty one. So being killed by a clean knife is good?
That is completely illogical!
Thanks again for an informative article . . .
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.
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.
It is never a good idea to mix pesticides together. They could react chemically and deactivate each other. For commercial products it is best not to tadd anything to them.
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.
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.
BEST THING FOR WEED IS THE PUll them out… Fashion way !! Just pull the weeds out by hands AMEN..
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.
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.
The problem with salt is that it dissolves very easily in water. So rain will quickly wash it away.
some of the problem with the bad reputation for roundup and the dislike for monsanto is the lies that are told about glysohpate. They are a big company with big money that speaks, for them it’s all about the profits and companies like this have a history of telling lies or hiding the truth about products or use testing companies that are paid big money to get there results that they want.
Re: “monsanto is the lies that are told about glysohpate” – which lies? Also provide references supporting your arguments.
hotwired, Glphosate has a very high KOC which means it binds to organic matter in the soil. Unless you are using it on a beach sand you will not have carryover problems.
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!
to Mr Robert Pavlis,
After reading this blog for 20 minutes. I am stronger about not using Roundup than before I came across this dialog. Mr Pavlis’ insistance on his ‘rightness’ and unwilling to bend, tells me, he considers his point of view the only one worth listening to. There are many points of view, conditions, climate, soil, etc. Over time, we will know more about the dangers of Roundup, but especially more about the dangers of those who adamently support Roundup.
I am not presenting my point of view!!!!
I am presenting what science has established as facts.
You have presented no science to support your position or to dispute the facts.
Wait, I thought science establishes our best known understanding of a subject, to be vigorously challenged and defended. It’s discouraging when Business and Marketing weigh heavily into Science.