When it comes to an organic weed killer that works, there are few options. One option is a homemade organic weed control recipe that’s rolling around the Net right how and I thought I’d check it out.
The Basic Recipe
- Vinegar: 1 gallon / 4.5L
- Liquid Soap: (note this is not detergent but soap) a few squirts to act as a surfactant (make the spray spread evenly and stick to the leaves)
- Salt: 2 cups (I no longer use but you’ll find it in many recipes. I didn’t find it helpful)
- Cooking oil: half-cup.
How To Apply:
With a regular garden sprayer until all leaf surfaces are wet.
How Often To Apply
- Use a concentration that burns the leaves dead.
- Repeat as soon as the new leaves unfurl.
- Repeat as often as needed until leave no longer regrow.
I’ve run multiple tests with varying strengths of Vinegar and here are the results.
Household Strength Vinegar (3% Acetic Acid)
I did this experiment with household strength vinegar and there was essentially no impact on any of the plants I sprayed.
This is contrary to what many websites will say but the reality of my tests on plants such as grass, dandelion and burdock didn’t produce a single shred of killing action.
Pickling Strength Vinegar (7% Acetic Acid)
The same recipe as above but with a 7% Acetic acid vinegar. This is normally sold as pickling vinegar.
Some burning and spotting of some leaves (Aegopodium) but total wilting of dandelion leaves. Rebounded the next day with some burning/spotting. Repeating immediately burned them to ground. The plant regrew within a week.
The mature thistles I sprayed started wilting within a half hour of spraying, looked quite ill at 5 hours but at 18 hours had rebounded to upright with burning and spotting on the leaves.
Not a kill at all for this highly touted organic weed killer. I’ve used it but no longer consider it worth the time for the minimal effect it has – the 10% below is far better and only slightly more expensive.
Household Cleaner Strength Vinegar As An Effective Organic Weed Killer (10% acetic acid)
Now, we’re seeing burning and wilting without a recovery by the original leaves on many plants.
But all perennials regrow as expected (while annual weeds do not obviously).
Acetic Acid at 20%
This stuff burns every plant on my tests and the leaves are totally brown and dead.
Annuals of course do not recover but perennials such as dandelions begin sprout new leaves within a day.
This is expected as acetic acid does not kill the plant but merely burns its leaves.
Depending on the strength of the acetic acid, it has a variable impact on leaf surfaces in my trials. The thicker leaved and aggressive growers seem to be the least bothered.
I have experimented with this homemade organic weedkiller for several years after I wrote this original report. The addition of soap is critical while the salt is helpful but not critical.
The oil does seem to help and I use the cheapest cooking oil I can find at approx 1 cup per gallon of vinegar.
My normal spray now doesn’t use salt.
- 1 gallon of 20% Acetic Acid (minimum of 10% acetic acid. higher is better)
- 1 cup of vegetable oil
- 2 tablespoons liquid soap
It takes several burns to kill off perennial plants and sometimes several years (can you say Aegopodium?) to really whack the plant to the ground.
It took 4 years of regular spraying to wipe out the Aegopodium. It might have been shorter but I did allow it (stupid me) to recover strength a few times in the second year. When I got serious in year 3, it pretty much disappeared by year 4. Year 5 was clean.
Environmental Impact of Organic Weed Killers Using Vinegar and Salt
It is well known that salt has a negative effect on the growth of plants (the Romans pretty much took care of the Carthaginian Empire by salting their fields after the third Punic war)
The problem for us is the long term effect of salt. It is washed down into the ground water by rains and in some areas and climates, this is going to be a problem.
Let me be crystal clear.
Household vinegar does not work as a herbicide contrary to much of what passes for garden advice on the Internet.
Pickling vinegar has a minor impact while the 10% cleaning solution has a decent burn on most plants.
Caution: Do wear protective breathing masks when spraying these products – whether you mix them yourself or purchase commercial equivalents. The tiny spray droplets are quite acidic on lung tissue.