Vinegar is good for destroying weed leaves, but it doesn’t kill weeds down to the root. As a natural alternative to weed killers, vinegar is typically only effective at killing seedlings that are less than 2 weeks old. Established weeds can survive vinegar applications and grow new leaves.
If you’re wondering if vinegar works as well as weed killer, here are some essential points to keep in mind:
- The active ingredient in vinegar is acetic acid, a desiccant that dries out and “burns” whatever organic material it touches. You can see results when you apply vinegar to weeds and grasses in as little as 1 hour.
- The acetic acid in vinegar is not absorbed by plant systems the way chemicals in commercial weed killers do, so it doesn’t travel to the roots. Also, vinegar is quickly neutralized by contact with soil. This means vinegar is very unlikely to penetrate to the roots.
- Vinegar is a “natural” alternative to weed killer but acetic acid is harmful to any plant, animal, or insect (including bees and other pollinators) that it touches.
- Standard vinegar contains 5–7% acetic acid and is safe to handle. Some gardeners recommend horticultural vinegar, which contains 20% acetic acid, for weed control. However, horticultural vinegar is an extremely strong acid that is dangerous to skin, eyes, and mucus membranes. It also corrodes wood, concrete, and some metals. It should be used with extreme care.
With these facts in mind, you may think twice before using vinegar as a weed killer. All-natural methods, such as hand-weed, mulching, and tarping are often safer for your garden than vinegar and more effective means of weed control.
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Does Vinegar Kill Weeds Permanently?
A single application of vinegar sprayed onto young weed seedlings may kill them permanently. In the case of mature weeds and grasses with established roots (those over 2 weeks old), vinegar will not permanently kill the plant.
An established dandelion, tuft of crabgrass, or any type of broadleaf weed will initially appear to suffer from a vinegar application. Within 1–24 hours, you will begin to see leaf damage. The weed’s leaves will turn brown and the plant will appear dead. This is only temporary. Because vinegar does not kill plant roots, the weed will use the stored energy in the root system to grow new leaves.
Your only hope of killing an established weed with vinegar is to spray repeatedly before the plant can form new leaves and replenish its stored energy. This can take many applications, and because many weeds grow so quickly, if you don’t spray vinegar for a day or two, the weeds will come roaring back.
Does 20% Vinegar Kill Weeds?
Horticultural vinegar contains up to 20% acetic acid, making it 3–4 times stronger than the standard vinegar found in your home. If regular vinegar isn’t killing your weeds, you may think it’s time to step up to the stronger stuff.
The truth is, 20% acetic acid vinegar is only marginally more effective at killing weeds than weaker vinegar. It may kill some weeds, but most will survive an application of horticultural vinegar. There are two reasons for this:
- Vinegar has to make contact with a part of a plant to kill it. Unless you soak the soil deeply enough to saturate the entire weed root, the plant will survive. In contrast, commercial weed killers are absorbed by the plant and passed from leaves to root to attack all plant systems. Plants do not absorb vinegar.
- Acetic acid is quickly neutralized by soil, rendering it harmless. Unless you apply very large amounts of vinegar, it will soon be washed out of the soil.
On top of vinegar’s ineffectiveness as a weed root killer, 20% vinegar is a dangerous and corrosive substance. When working with horticultural vinegar, you must wear gloves, goggles, and a mask. 20% vinegar can cause chemical burns, blindness (if it makes contact with your eyes) and the fumes can even burn your nostrils. Additionally, 20% vinegar corrodes concrete, metal, and wood. The small boost in weed-killing effectiveness isn’t worth the risk to yourself and your property.
Does Vinegar and Epsom Salt Kill Weeds?
Many at-home weed killer recipes suggest mixing Epsom salt or table salt with vinegar. This is very risky. We know vinegar doesn’t kill weeds to the root, which makes it an ineffective weed killer. Salt, on the other hand, is a dangerous additive to any weed killer because it is so effective at killing plants and preventing new growth. Simply put, salt turns soil into a “dead zone” where nothing will grow.
Salt works slowly, taking 10 days or more to kill weeds. However, once salt is present in the soil, there are a number of risks:
- Salt kills all plants and renders soil inhospitable to plant life. If salt is present, plants will not grow.
- Salt does not neutralize quickly. It can remain in the soil for years.
- Salt added to the soil can be carried to nearby portions of your yard and garden by water runoff, increasing the size of the salt “dead zone”
If you use salt as a weed killer, be very careful to apply it only in areas where you want no plants to grow and where water runoff will not carry the salt to any plants you wish to keep alive. It is not recommended to spray a vinegar/salt mixture in your lawn or garden, where it can cause lasting damage.
Will Apple Cider Vinegar Kill Weeds?
Like all kinds of vinegar, apple cider vinegar contains acetic acid. Typically, apple cider vinegar contains 5–6% acetic acid. This means apple cider vinegar is no better or worse at killing weeds than the other kinds of vinegar in your cabinet.
If you apply apple cider vinegar to any plant’s leaves, they will be burned by the acetic acid and the plant will appear “dead.” While destroying the leaves is certainly harmful to the plant, mature weeds are notoriously hardy. Apple cider vinegar will not kill the weed down to the roots. In the majority of cases, the weed will resprout from the roots a few days or weeks after an application of apple cider vinegar.
Rather than reach for the apple cider vinegar as a weed spray alternative, you’ll be better served killing weeds by hand-pulling. Techniques like digging out weeds or smothering them with mulch or tarps are the best natural methods for weed control.
How Long Does it Take to Kill Weeds with Vinegar?
You will begin to see yellowing or browning of weed leaves between 1 and 24 hours after vinegar application. The exact timing of results depends on temperature, amount of sunlight, and weed species. In most cases, you will see the full effects of your vinegar spray within 5–7 days. That is, the leaves of the weed will be yellow and/or brown.
That doesn’t mean the weed is dead though. Vinegar won’t attack weed root systems, so a seemingly dead weed can make a full recovery from a vinegar application within days or weeks.
To truly kill a weed with vinegar, you will have to spray the plant each time it attempts to sprout new leaves. This method may take months of repeat sprayings, and still may not be entirely effective. To entirely kill weeds, consider an approach that attacks the roots (commercial weed spray or hand weeding) or deprives the weed of sunlight (covering with mulch or a tarp).
How Long Does Vinegar Last in Soil?
Vinegar breaks down quickly in soil, which is one of the reasons it is so ineffective at killing weed roots. The amount of vinegar that reaches the soil when you spray a weed will break down in 2–3 days, sooner if you experience rain or you water the soil.
If the soil is thoroughly saturated with a large amount of 20% vinegar, the acetic acid may linger up to 30 days, rendering it more difficult for plants to grow there, but this requires a very large amount of vinegar. A small amount of vinegar spray will not achieve these levels of toxicity.
Using Vinegar to Kill Weeds
Vinegar spray is a quick way to wipe out weed seedlings, but because the acetic acid in vinegar does not penetrate the soil, it will not kill mature weeds down to the root. Because of this, vinegar is not an effective solution for getting rid of established weeds such as crabgrass and dandelions. Rather than using a vinegar-and-salt solution, or dangerous horticultural vinegar, the most effective natural weed-killing solutions are hand-digging weeds or employing a ground covering (mulch, tarp, landscape fabric) to kill weeds completely.