Many websites recommend using vinegar as a weedkiller (herbicide) and yes, the typical white vinegar found in your kitchen does have some effectiveness in controlling weeds. But it’s not a miracle cure. In fact, far from it! I suspect that most gardeners will be a little disappointed with the results.
First, it must be understood that vinegar is a contact herbicide: it has to be sprayed on the green parts of the plant. It will not penetrate the plant’s cells, nor will it reach the roots. Plus, it has no residual effect. As soon as it’s dry, it loses its efficacy, then it quickly decomposes. At least this means there isn’t much a of delay before you can sow or plant in the treated area. 24 hours will suffice.
White vinegar normally contains 5% acetic acid, more rarely 7%. That’s great for pickling cucumbers, but not usually enough to kill anything other than young weeds, especially seedlings. Cleaning vinegar or double strength vinegar (found in the cleaning department of most hardware stores) contains 10% acetic acid and you’ll find it a more effective weedkiller: it can kill the maturing leaves of most perennial weeds, but it rarely kills those that are fully mature. Instead, often only the leaf tips and edges are damaged.
You’ll therefore find that vinegar is not a very effective herbicide in the summer or fall, when most leaves are mature. It will give much better results when you use it in spring, when leaves first emerge.
To effectively kill mature leaves (summer and autumn leaves), you have to go up a grade. Horticultural vinegar contains 20% acetic acid, so four times more than typical white vinegar. It can kill mature leaves … but it’s important to point out that it’s a fairly toxic product. You’ll need safety goggles and protective gloves. And the smell is intense! Yes, tears will come to your eyes when you use it! Also, horticultural vinegar can be difficult to find locally. You may have to order it by mail.
Dead Leaves, Live Roots
No matter the type of vinegar, it will only kill the foliage. And that’s sufficient when you want to control seedlings and most annual weeds, but in general, perennial weeds (horsetail, plantain, quack grass, etc.) will regrow quite quickly from the roots since they aren’t affected by the spray. That means you have to repeat the treatment after a week or two, when leaves reappear. And then again if they grow back. Depending on the type of plant, its state and the type of vinegar used, several treatments will likely be necessary to permanently control most perennial weeds.
To Make Vinegar More Effective
To make the herbicide more effective, add a little pure soap, such as insecticidal soap, to the liquid, perhaps 1 teaspoonful (5 ml) per quart (liter) of vinegar, to help the product stick better to the foliage. Many websites further recommend adding salt to vinegar, but you’ll then be playing with a much more dangerous product. Remember that salt can sterilize the soil permanently and is certainly not an environmentally friendly weedkiller.
Protect Your Other Plants
Vinegar is a non-selective weedkiller (total weedkiller): that means it affects any plant, be it a weed or one you want to keep. You therefore have to apply it with great care.
Usually, it’s used for weeds growing in places where you don’t want any plants at all, such as in cracks in patios, sidewalks, driveways and the like, or to kill weeds in empty vegetable beds before sowing or planting crops. It’s certainly not a “weedkiller for lawns”: it will indeed damage or kill grass. True, it can be used for spot treatments (killing individual weeds in the lawn), but then must be applied with the utmost precaution, being sure to spray only the weed, not its neighbors.
Using Vinegar as a Weedkiller
Spray vinegar on a sunny, dry day and certainly never when it’s windy. Ideally, the air temperature should be above 70 ° F (21 ° C). Avoid applying it on surfaces that can be tarnished by acidity and that includes many metallic surfaces including those found on garden furniture.
Now, it’s up to you to decide if the vinegar is really the right product for controlling the weeds under your conditions. Often, hand pulling is more effective!