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
After reading your article I did a bit more research into the commentary re: Roundup & links to cancer.
It is classified as a Class 2a substance… What is a Class 2a substance you ask?
It means it is Probable it is carcinogenic with limited to no evidence to humans, but sufficient to animals…
What what is in the Class 2a category…
Red Meat, Working night shift, Working as a hairdresser….
There are things we regularly put in our body which are known carcinogenic substances (Class 1), such as alcohol…
In summary, looks like I’m continuing to use Roundup…
Do you have a link for that? I think you are looking at an old WHO rating that is based on a false review. A newer review by WHO came to the conclusion there is no evidence of cancer.
If roundup is so safe why the warning labels to not get it on your skin?
Labels are there for people who do not know how to handle chemicals. You should not get concentrated chemicals of any type on your skin.
Good grief. Social media sucks. Everyone thinks they are important and deserve a platform.
Thank you for your article. It has helped me decide what to spray where on my property.
Well, I have never tried table vinegar or pickling vinegar. I use 20-25% acetic acid and add maybe 2-4 drops of liquid dish soap. As I was learning how to make it work I did get some return growths. So I experimented and found that if I soak the base area of large (over 1ft high) dandelions then return after making my 1st round and give another dose to the base of the dandelions and finally put the tip on wide spray and douse the entire plants, they go away and do not come back. I believe that the soap allows the acetic acid solution to break surface tension and sink into the ground. I believe the 1st dose might lose a little potency reacting with elements in the soil then the 2nd dose goes right in and gets to the roots. This has been quite effective for me. IN fact, even on the smaller plants I do fire some concentrated shots at the base of the plant so it will soak in. Unless the plant is a serious acid loving plant this seems to knock them out completely. Also, many sources claim it should be applied on a sunny day. I find I have my best results on cloudy days if it does not rain and wash it away.. No wind, lower temps, no direct sun allows it to penetrated better.
Just my 2c worth. I really thought I had been tricked the first time because it does require a little thought and planning to get good results and make the expense worthwhile.
You had good results because you applied common sense, observed effects then adjusted to try for improvements. The simple addition of a wetting agent helps overcome the plants evolved protective coatings. Applying under conditions that improved the contact of the chemical to the plant. All perceptive adaptations that showed better results. I am glad you didn’t use any salt(NaCl). It is seriously destructive to soil structure and as you mentioned persistent never breaking down only leaching to another area to cause additional destruction. One of the major pollution issues in our country is NaCl contamination of wastewater from water softeners that cannot be removed from the water by affordable treatment means making the water destructive for irrigation, among other benefial uses. The Na is monovalent and breaks down the soil particles and occupies cation soil particle sites that help hold beneficial nutrient cations until plants can use them. The soil percolation rate and tilth is damaged.
Mr. Pavlis sir… Why dont we try it in the fish pond with live fish of course… 1 liter of round up in 1 pond and 1 kilo of salt in the other pond… I liter of vinegar in the 3rd pond… To test the safety of youre claims.
I made no claims about harming fish!
How big are your ponds? Without knowing the concentration the test is not going to tell you anything.
My claims are based on real scientific studies – thousands of them.
Nestor you forgot the grape juice, that concoction you suggest for your fish pond would pickle your fish, what you are suggesting is foolhardy & not back up by science. You would do well to read & digest what Robert Pavlis writes, then you might learn some true FACTS
science….. lol…. like we still trust it after the last few years.
If it’s as safe as salt or vinegar why not have some on your salad too!
Do you eat things just because they are not toxic?
you will find, that it is already in your salad.
Glyphosate is safe and effective, in my opinion. However, it is very expensive when purchased retail in the relatively small quantities that amateur gardeners use.
Cheap, standard vinegar (i.e., 4 to 5% acetic acid) is not very effective when used unmodified because weeds—like virtually all plants—have a thin waxy film on their surface cells which prevents the vinegar from staying put and thoroughly wetting the surface.
I mix about 3 gallons of household vinegar with a pint of cheap dish soap and spray it onto weeds with a typical hand-pump spray rig.
The addition of the dish soap makes all the difference in the world to the performance of the vinegar—it causes the acetic acid to evenly wet the surface of the weeds and it presumably helps the acetic acid to penetrate the waxy surface layer of the weeds it is applied to.
This remedy is very effective on broad-leaf weeds like clover, oxalis and others. It also works on foxtails and other tough weeds, but may require two successive applications for some weeds. If the weeds are exposed to direct sunlight for several hours after application that definitely speeds up the killing time.
Generally, it takes about 1 or 2 full days after application to see the complete results….but it’s worth the wait!
1) The soap may help the vinegar damage leaf tissue – soap is a surfactant and these are routinely used to help chemicals stick to plants.
2) The problem with vinegar is that it is not absorbed past the leaves. It in effect burns the leaves, leaving the crown and root system intact. That is why they call it a contact herbicide – it damages only what it contacts.
3) You have to wait for a couple of weeks to see if you killed the weed – not just 1 or 2 days.
https://youtu.be/NF1Li-RCZso
Re: Point #3 by Pavlis is incorrect. I stand by my estimate of weed-killing with vinegar-dish soap mixture requiring only 1 or 2 days (not weeks). As indicated, foxtails and some other weeds may take a little longer, requiring two successive applications; however, broad-leaf weeds like oxalis are quick to succumb.
Labs have tested vinegar – it does not kill weeds. Even 30% acetic acid will not kill all weeds. The science on this is clear.
Thank you Robert for a great article, it might be a few years old, but the conclusions drawn never age