A while ago I wrote about using vinegar as a weed killer, in Vinegar Weed Killer Myth and reported on the scientific evidence for vinegar weed killer. It does not kill larger weeds with established roots, but can have an effect on seedlings. Vinegar is recommended so much in social media that I decided to give it a try myself.
I ran a few simple experiments to see how effective vinegar is for killing weeds.
Vinegar Weed Killer
In this post vinegar refers to the stuff you can buy in a grocery store. I decided to use pickling vinegar with a 7% acetic acid concentration. Around here it is the same price as the 5% strength, so you might as well buy 7%. Besides it might work better.
This post does not discuss 20 acetic acid which is a dangerous chemical that does kill some weeds.
Homemade Weed Killer: Vinegar
So vinegar kills some weed seedlings, but mostly it just burns off the green parts above ground. I was curious to see how effective it is. It might be a worthwhile product to use on a patio where a lot of the weeds are seedlings.
I just happened to have some weeds in my patio. OK, I always have weeds in my patio, but I have a garden open house in two weeks and need to remove them to make people think that I am always weed free.
People claim that the weeds “die within hours” of being sprayed. After a few hours I saw some browning, but not very much. I decided to wait until the next day before taking the following pictures.
24 Hours Later
The weeds in the sprayed area do look quite dead. The green ones in the top and upper right corner of the picture were not sprayed.
You can see that some of the smaller weeds have brown leaves, but the larger weeds seem to be unaffected. So I gave them a second good soaking.
After Second Spraying
The vinegar did not do a good job on the large weeds. Even after several days, they had some green leaves. I ended up removing them by hand before the open house just to clean things up.
Eight Weeks Later
It is now mid August, and the above picture shows the area where the small weeds were sprayed. They did not regrow. The one large weed is a crabgrass that has recently grown from seed. I have to admit, it was more effective than I expected. I can understand why people claim vinegar kills weeds.
Homemade Weed Killer: Vinegar vs Crabgrass
The above experiment showed that vinegar does kill small seedlings. By mid August the spaces between my flag stone pathway was full of crabgrass. I wondered if vinegar could be effective against crabgrass?
I used the same pickling vinegar as in the above experiment, and sprayed the pathways.
Not all of the weeds in the pictures are crabgrass, but many of them are.
After Pictures (24 hours after being sprayed with pickling vinegar):
The plant leaves are certainly brown, and to the untrained eye – they look dead. The green weeds in the upper left corner of the closeup view are weeds that did not get sprayed.
If you get real close to the weeds, as in this next picture, you will see that the crown of the plant and the stems are still green. For the most part, only the flat blades of the leaves were damaged by the vinegar, and then only the ones that got into direct contact with the vinegar.
A week later, and the weeds were growing back with new leaves. They were not killed by the vinegar.
Vinegar is a Contact Herbicide
The above picture shows that the vinegar only affects the parts of the plant it contacts. That is consistent with the scientifically reported mechanism for vinegar. It affects the cell membranes of a plant, causing rapid breakdown/desiccation of foliage tissue on contact (ref 1). It is a contact herbicide only damaging the green parts it contacts. The rest of the plant, and especially the roots are unaffected by the vinegar. This explains why it is not a very good herbicide for larger plants.
2) Photo Source: all pictures by Robert Pavlis