For eco-minded gardeners, chemical herbicides are not an option. But we can’t just let thistles and bindweed take over! If you’ve tried many weed prevention methods but still need a quick fix, a vinegar weed killer seems like the perfect solution. However, there are a few things you should know before you douse your weed infestation in vinegar.
Let’s dig into the science and practicality of using vinegar to kill weeds.
The Short Answer
For many gardeners, hand-weeding, mulching, and tarping are more reliable alternatives.
Vinegar is a possible organic weed killer when used correctly, but it isn’t the best option. USDA research shows that 5% concentration and 10% concentration are effective for killing young broadleaf weeds under two weeks old. It may not work as well for grasses unless used in high concentration.
However, higher concentrations contain more acetic acid, which can be corrosive and more dangerous to your skin and eyes. As the saying goes, “the dose makes the poison,” and highly concentrated vinegar is not a very safe solution for the garden.
Concentrated horticultural vinegar with high amounts of acetic acid is needed to kill older, mature weeds. Spot applications can reduce weed pressure. Even aggressive species like Canada thistle can die from high-concentration spray, but reapplication may be necessary for perennials with aggressive root storage structures because the acetic acid only kills the top of the plant. Organisms in the surrounding soil will be harmed after repeat applications.
Ultimately, vinegar is not the best weed control option. For many gardeners, hand-weeding, mulching, and tarping are more reliable alternatives.
The Long Answer
Preventative techniques like mulching and tarping are the most promising long-term solutions.
Weeds are one of the greatest threats to an organic landscape, specifically one where you aim to minimize soil disturbance with no-till techniques. Aggressive perennials like thistles, bindweed, and grasses are particularly problematic for gardeners. Fortunately, you don’t need to turn to chemical herbicides, and hand-weeding is not the only alternative.
Preventative techniques like mulching and tarping are the most promising long-term solutions, but quick applications can help cut back on heavy infestations. While vinegar is most effective on young broadleaf weeds, it can be used in higher concentrations to combat mature plants and sometimes grasses.
The most active weed-killing ingredient is acetic acid. Household vinegar contains about 5% acetic acid. This component is naturally occurring, but it can kill young, unwanted plants. More concentrated solutions have higher concentrations of acetic acid, requiring more careful handling. Even though it is an organic alternative to herbicides, it can still burn your skin or eyes if used improperly.
Take all of this into consideration as you weigh the pros and cons of using vinegar to control weeds:
Pros
A cheap, accessible, and safer alternative to herbicides.
This is a cheap, accessible, and safer alternative to herbicides. If used in a low concentration and at a low frequency, it is unlikely to harm you or your plants. However, it is best used only as a last-resort option or as part of integrated control. Weed prevention and management methods are more effective for long-term sustainability.
The benefits of using household vinegar to kill weeds include:
- Quick Action: Depending on the concentration, it can kill plants within 8 to 48 hours.
- Very Effective for Small Plants: With household vinegar, it is easy to knock out overgrowth of small weeds under two weeks old.
- Great for Broadleaves: Broadleaf (non-grass) species die quickly after treatment.
- Useful for Lawns: Since lower concentrations are less effective on grass, this could be a useful herbicide alternative for small broadleaf species in lawns.
- Biodegradable: It naturally biodegrades in the soil when applied at a low frequency.
- Salt-Free: One of the biggest issues with synthetic herbicides is salt residue buildup, which rapidly degrades soil. You can knock out the unwanted plants without leaving salts in the ground.
- Low Concentrations Are Safe: Household solutions with less than 5% acetic acid are safe to apply without skin protection.
Cons
It can still be problematic in high concentrations.
While vinegar is technically all-natural and organic, it can still be problematic in high concentrations. Household vinegar is relatively benign, but concentrated cleaning or horticultural formulations could pose more risk than they’re worth.
Research shows that acetic acid concentrations over 11% can burn your skin and cause permanent eye injury or blindness if it reaches your eyes. While at first, it seems like a pleasant home remedy, it becomes more like a chemical as the concentrations increase. Horticultural solutions are typically around 20% acetic acid, which is a much more corrosive chemical than the household kind.
Here are the key drawbacks of vinegar for weed control:
- Dangerous to Skin and Eyes: The most obvious risk of using any concentrated chemical is its danger to human health. High concentrations of over 11% acetic acid can be dangerous when used without personal protective equipment.
- Less Effective for Grasses: Perennial grasses like quackgrass and crabgrass are difficult to kill and may require very high concentrations. This damages soil content.
- Less Effective for Mature Plants: A homemade spray (non-horticultural) is really only advantageous for tiny weeds, which are easy to kill with other methods.
- Only Targets Above-Ground Parts: The desiccating (drying) action of this compound only targets the stems and leaves. The roots remain unaffected below the surface.
- Metal Reactivity: Vinegar can react with iron, tin, and aluminum, so it should not be applied with metal equipment.
- High Concentrations Often Needed: While low concentrations can knock back small unwanted plants, higher concentrations of 20% acetic acid are required to significantly control plants like thistle, pigweed, or quackgrass.
- Allergic Reactions: It can be very irritating to the skin and lungs.
- Odor: This application gives off an obvious odor that many find bothersome.
- Reapplication: You may need to apply many times to reach your desired result.
After you consider the need for high-concentrations and the reapplication requirements, it often makes sense to just pull out the weeds or use a different method.
How Vinegar Kills Weeds
High concentrations can kill desirable plants, too.
Acetic acid is vinegar’s active plant-killing ingredient. Its mode of action is technically plant desiccation, which means it makes plants dry out. Acetic acid breaks down the plant cell walls on contact, causing the plants to lose their fluids and die.
This compound is non-selective, so applying it to your entire garden is not a good idea. It can kill desired crop plants just as rapidly as it kills weeds. However, since it is usually applied directly to concentrated overgrowths of small weeds, the acetic acid is unlikely to reach your taller, mature crops. Horticultural vinegar can quickly damage soil, though.
The Verdict
A handheld hoe or hori hori knife may require less overall effort to kill weeds.
A handheld hoe or hori hori knife may require less overall effort to kill weeds. Vinegar is only reasonable to destroy clusters of small broadleaf species. Even then, it may not warrant the effort. The compound only targets the above-ground plant parts, so it is not super efficient at removing perennials.
The household compound is cheap and accessible, but the low concentration of acetic acid in regular bottles may render it ineffective. While high concentrations of acetic acid in horticultural products are very effective at killing large plants and grasses, they are much more dangerous to use. Moreover, it takes a lot of effort to fill a sprayer and apply it all over your garden several times per week.
As a former professional organic farmer, I recommend avoiding vinegar. There is no need to spray it in an organic garden. Instead, use alternative prevention and management methods to create long-lasting weed control with less overall effort.
Alternatives to Weed Sprays
Never leave soil bare, as this can welcome weed seeds to germinate.
Instead of spraying weeds, think about how you can prevent them and keep them out of your garden. These practices are safe, easy, and sustainable. They build over time to create longer-lasting weed control by lessening the overall volume of weed seeds and aggressive perennial roots sprouting in your garden.
Options include:
- Mulching: The most obvious way to suppress undesirable plants is to mulch the soil surface. Never leave soil bare, as this can welcome weed seeds to germinate. Deciduous leaves and straw are the best options.
- Compost Application: Apply a layer of compost to the top of your beds every season to enrich the soil and bury any weed seeds that are waiting to germinate near the surface.
- Hoeing: A scuffle hoe (hula hoe) is an easy handheld tool that slices plants just below the soil surface, killing them instantly.
- Hori Hori: This special gardening knife is helpful for lifting deep taproots from the soil, but it does require getting on your hands and knees for manual removal.
- Tarping: For heavily weed-infested areas, a tarp can smother plants in a couple of weeks. This method is completely passive and only requires laying the tarp and then lifting it later. You may water in between applications to encourage more weeds to sprout under the tarp. After they re-sprout, re-cover them to prevent them from accessing sunlight. This can help exhaust the root systems of perennial plants.
- Ground cover: Grow low-height ground cover plants like creeping thyme or microclover to outcompete weeds and add aesthetic “living mulch” to your garden.
- Cover Crops: Plant weed-smothering cover crop blends in empty beds to protect the soil from an overgrowth of unwanted plants. Cover crops simultaneously enrich the bed with nutrients and organic matter.
- Preventing Weed Seeds: The most important means of long-term weed prevention is to follow this simple rule—Never let weeds go to seed! At the very least, you should mow or chop off them at the base before they set seed. As soon as you see flowers, they need to go! Otherwise, they can spread thousands of progeny and create years of weed problems.
FAQs
Homemade sprays will permanently kill small, young weeds. However, unless it is horticultural vinegar, it is unlikely to kill larger, mature plants because the active ingredient (acetic acid) only targets the above-ground plant parts that it physically touches. Moreover, higher concentrations of 10 to 20% acetic acid are necessary to kill aggressive plants and grasses.
USDA research shows that 5% acetic acid household solution can kill weeds within about 8-48 hours when applied directly to the top growth. Concentrated horticultural solutions of 20% acetic acid can kill the unwanted plants in about two hours. Aggressive perennials (particularly grasses) may take longer to die, or reapplication may be required
