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.
1) Glyphosate technical Fact Sheet: http://npic.orst.edu/factsheets/glyphotech.html
2) All photos by Robert Pavlis