Various blends of vinegar, salt and dishwashing liquid being used as an "organic" or "natural" or "no chemicals" weed killer are all over Pinterest and gardening blogs. They claim it's faster, cheaper and better than "Roundup" herbicide.
I have no clue how a blend of a commercially produced acid and a concentrated household detergent could be considered either "natural" or 'chemical-free". But I'm all for cheaper and better, so I tried it. I did a comparison test in early March by spraying two clumps of my worst weed, annual blue grass.
|One side is vinegar, salt and dishwashing liquid|
the other is Glyphosate.
You guess which is which.
The Commercial Herbicide
If I use herbicides, I use glyphosate, the generic herbicide version, not whatever blend is currently being sold as trademarked "Roundup"*.
Glyphosate has close to a 100% kill rate with one application if you follow the directions. It's a slow herbicide, but it's fast enough that if I spray on a weekend I can see what I missed the following weekend. The sprayed weeds are yellowing and wilting and the green ones are the ones I missed.
The Vinegar-based Recipes:
With lots of salt: "2 cups table salt, 1 gallon white vinegar (make sure it has 5 percent acidity)". Gads, the salt content alone could sterilize the dirt and prevent anything from growing. Have they not heard of salt damage? Carthage?
With some salt: "3 gallons for around $4.00 Worked better than Round Up killed the weeds/stray grass on first application. One gallon of vinegar, 1/2 c table salt, 1 tsp Dawn." This is the recipe I used, cut down to make a pint of the mix.
Without salt, and with a dislike for the ever-popular Dawn brand liquid detergent: "4 C. Apple Cider Vinegar, 1 t. Dish Soap (not Dawn) Mixed in a spray bottle. Add soap, then vinegar. Don't shake (BUBBLES) It all seems so gentle and harmless but remember, vinegar is acidic and not selective when sprayed on plants."
Is It Cheaper?
I can buy generic glyphosate concentrate at Walmart for under $8. Mixed with tap water at the recommended dilution, it makes 10 gallons of herbicide, so that's 80 cents a gallon for the commercial herbicide.
Vinegar - plain white generic vinegar with 5% acetic acid - is $1.89 to $2.12 a gallon at the local stores, so the vinegar mixes are 2 to 2 1/2 times more expensive than my generic glyphosate mix.
It's only cheaper if you compare the vinegar solution with buying ready-mixed containers of herbicide, which is not being thrifty. Convenient, but for the few minutes it takes to mix up a gallon of weed killer it's not worth the added cost.
Is it Better?The vinegar spray looked impressive 3 days later. The clump was yellowing and turning brown at the tips. The glyphosate sprayed clump was still green. Unfortunately, I didn't take a closeup picture.
Ten days later I checked again. Uh-oh! The grass given the vinegar treatment had recovered, showing fresh green color. The glyphosate treated clump was yellowing as expected, with just a trace of green at the tips of the seed heads.
|Glyphosate on the left, vinegar mix on the right, 10 days after spraying.|
Three weeks later it was a clear win for the glyphosate. The vinegar treated clump was green and healthy, the glyphosate treated one was dead.
|Glyphosate, 3 weeks later|
But, but …… say the fans of the vinegar mix .... you just have to keep treating the weeds and they will eventually die. That may be true, but if I have to spray the weeds several times with a solution that is twice as expensive as the glyphosate, tell me again how it's cheaper and better. Also, annual weeds die here when the weather gets hot. The purpose of killing them is to prevent their setting seeds and multiplying all over the yard.
* NOTE: “Roundup” used to be just glyphosate, but Monsanto has added some other herbicides to it to give it a faster “knockdown”. Apparently most of the gardening public wants to see weeds appear to shrivel and die by the next day.