RoundUp is a bad word in our house. Thankfully, this sentiment is spreading. More people are becoming aware of the dangers of using long-lasting chemicals, such as glyphosate, that have a devastating impact on the environment for weed control.
And while that’s great news for the environment, there are a bunch of weeds growing up through my flagstone patio that are pretty happy I don’t use RoundUp either.
That is until recently.
I discovered the magic that is horticultural vinegar. (This is the exact brand I use.) With a quick application, my patio smells like a classic Italian sandwich for a couple of days, and the weeds shrivel up and die within hours.
Yes. I said hours. Those photos above were taken one hour apart.
This stuff is amazing both in its effectiveness and because it’s so much better for the environment. But it is still a potent acid, so it needs to be used with care. Let’s get into it.
What is Horticultural Vinegar?
Horticultural vinegar is basically white vinegar, but more concentrated. And white vinegar is just acetic acid mixed in a specific concentration with water.
Funny story.
One day, while working in the Biochemistry and Molecular Biology Department at Penn State, I wanted to make tea for my afternoon break. The electric kettle was disgusting and covered in scale. I searched the kitchenette cupboards for white vinegar so I could descale it, but couldn’t find any. Then I remembered, “Hey, Trace, you support six different labs. I’ll bet any one of them has acetic acid.”
So, I found one of the lab managers and said, “Could you make me some white vinegar? I need about a ¼ cup. 5% acetic acid, please.” And she did. I descaled the electric kettle. I had a great cup of tea—the end.
So, horticultural vinegar is acetic acid and water in a concentration of anywhere from 20-50% acid.
How Does Horticultural Vinegar Kill Weeds?
Horticultural vinegar works by burning the foliage of the plants it comes into contact with. The high concentration of acetic acid pulls moisture out of the plant’s cells, effectively dehydrating the tissue.
This process starts instantly. I was shocked at how fast it worked the first time I used it. By the time I had finished spraying an area, many of the leaves were already turning orange. Within an hour, they were all shriveled and brown.
While this looks impressive, it does come with a caveat.
Horticultural vinegar is amazing for killing annual weeds. The ones that pop up quickly and die off when there’s a drought or when winter hits. For tough, perennial weeds (usually the ones with long tap roots), the acid only kills off the above-ground portion of the plant. Often, the plant will grow back unless that tap root is removed, too. But we’ll get to that in a bit.
It’s also a non-selective herbicide. It will work on any plant you spray it on, the weeds…and your flowers and vegetables.
So, what types of weeds and areas are best suited for vinegar treatment?
Think of spots where you want a total kill and where you’re not worried about accidentally harming your prized perennials or beautiful tomatoes.
Cracks in driveways, sidewalks, patios, gravel paths, and other hardscaped areas are prime candidates. These are places where weeds tend to pop up where nothing else is supposed to grow anyway.
In garden beds, it gets a little trickier. It’s not suitable for spraying around delicate seedlings, vegetables, or flowers. However, if you’re careful and precise, you can use it along the edges or in between well-spaced plants.
What Do I Apply It With?
The best option is a pump sprayer. This is the one I use. I rinse it well after I’m done and spray clean water through it. That way, I can use it for applying foliar sprays and things like neem oil, as well.
You can also add a few drops of liquid dish soap to help the solution adhere to plants more effectively.
Killing Weeds with Horticultural Vinegar
How to Apply It
Be sure to wear proper PPE (personal protection equipment) when spraying. We’ll cover that later. Using your pump sprayer, move slowly and spray back and forth over the area you want to cover. For stubborn weeds, be sure to apply to the base as well.
Give yourself plenty of time and move carefully and slowly, paying attention so you don’t carelessly spray and damage a nearby ornamental or edible plant.
You want the weed or the area to be thoroughly wetted with the vinegar when you’re done.
When (and When Not) to Apply It
Timing matters when it comes to applying horticultural vinegar. The best time to spray is on a hot, dry, sunny day when temperatures are above 70°F. Sunshine accelerates the leaf-burning process, and dry conditions ensure the vinegar won’t be washed away before it takes effect.
Don’t spray on windy or rainy days.
Rain within a few hours of spraying can render your efforts useless, and windy conditions are a hazard because they can carry vinegar droplets onto plants you want to keep or onto you. However, rain within a couple of days after spraying can help break down the acetic acid faster.
How Often Should You Apply It
If you’re wondering how often to apply horticultural vinegar, the answer is it depends. For young, shallow-rooted weeds, one application is usually enough.
For tougher or more established weeds, you may need to repeat the treatment every couple of weeks. Keep an eye on the area and reapply as needed, but don’t go overboard. Repeated use in the same area can kill off the microbiome in the soil. While this may not be an issue in your gravel driveway, it very quickly becomes a concern if you choose to use horticultural vinegar in your garden.
For those pesky weeds with deep tap roots, wait a few days and pull the dead plant up by the root. Be sure to wear gloves. If you let the weeds sit for a couple of weeks, you can compost them after that, as the acetic acid will have broken down by then.
How Does it Compare to That Other Stuff?
Glyphosate works systemically—absorbed by the plant and killing it from the inside out—vinegar only damages what it touches. That means regrowth is more likely with vinegar, especially in perennial weeds.
But on the flip side, vinegar doesn’t cause horrific damage to the environment and waterways. And it’s safer when used responsibly. Like most answers to environmental problems, it’s a tradeoff: faster kill with longer-lasting results from synthetic herbicides versus more environmentally responsible spot control with vinegar, requiring more diligence and repeat effort. Plus, there is the bonus of no green guilt.
Safety & Environmental Precautions
I always get frustrated when people hear the word chemical and immediately think something is bad or dangerous. It’s equally frustrating when people hear the words’ natural’ or ‘organic’ and think something is safe and good. Duality is a common thing in the natural world, and we would all benefit from learning that chemicals aren’t innately bad and that natural isn’t always good.
For example, one of the most dangerous chemicals on the planet is virtually colorless, odorless and tasteless.
- It’s one of the chemicals always found in acid rain.
- The vaporized form of this chemical can cause severe burns.
- It’s a major component of toxic waste runoff.
- It’s often found in tumors of terminal cancer patients.
- It’s currently found in almost every lake, stream, river and ocean on the planet.
- And if you inhale this chemical, you’ll likely die.
What is it? Dihydrogen Monoxide.
I’m drinking it right now. It’s water. And it’s completely natural.
I hope I’ve made my point as we discuss the duality of acetic acid when it comes to safety.
Environmental Impact
One big question people ask is whether horticultural vinegar is environmentally safe. Yes. It’s safe.
If it’s used in high concentrations in the same area, over time, it can damage the soil microbiome.
Acetic acid breaks down quickly in the environment. It is both volatile (breaks down quickly) and readily biodegradable. It has a half-life of around 1 to 10 days, depending on the weather. (Rain will cause it to break down faster.) Soil microbes quickly metabolize it into carbon dioxide and water. It’s water soluble. These are all good things, as once it’s out of the bottle and into the environment, it doesn’t take long at all to break down.
Another concern often cited is runoff.
Let me be quite clear: runoff of any type is more of an issue in commercial farming than in your home garden. Granted, as responsible gardeners, we must still exercise caution when it comes to our fertilizer use. However, horticultural vinegar poses no runoff threat when used wisely around your lawn and garden.
An analysis by the EPA found that for acetic acid (horticultural vinegar) to have a negative impact on aquatic life, it would need to reach volumes of around 1 tsp of 20% vinegar per 1 liter of water.
I want you to let that sink in for a moment—1 tsp of horticultural vinegar per liter of water.
The stream that runs through my backyard is Spring Creek. It’s beautiful and well-known for its trout fishing. According to waterdata.usps.gov, approximately 232,200 liters of water per minute flow through that stream.
I could stand at the bank in my backyard and dump gallon after gallon of horticultural vinegar into the stream all day long and never come anywhere near the concentrations needed to harm aquatic life or raise the pH in the stream.
So yes, when used by the average home gardener, horticultural vinegar is completely safe for the environment. Just not the weeds you spray it on. The plastic jug it comes in is worse for the environment than the vinegar.
PPE Is a MUST – This Stuff is No Joke
Let’s talk safety. Acetic acid in these concentrations can cause burns. You need to be especially careful when handling it and applying it, as you would with any other household chemical you use. The stuff you use in your kitchen and make pickles with is anywhere from 3-5% acetic acid. Horticultural vinegar can be anywhere from 20-50% acetic acid.
Always follow the directions on the container. When applying, always wear closed-toe shoes, long pants, and a long-sleeve shirt. Wear rubber gloves, eye protection and a mask. Do not spray it on windy days.
Storing Horticultural Vinegar
Again, follow the storage directions on the container. It’s best to keep it in the container it came in. Store it in a cool, dark, and dry place, away from pets and children. Clearly label any sprayer you intend to use or keep horticultural vinegar in. Or rinse your sprayer thoroughly when you’re finished applying vinegar if you want to use it for other applications.
At the end of the day, horticultural vinegar and my propane weed torch are my go-to tools for dealing with annoying weeds that pop up in my driveway, stone patio and decorative gravel. When it comes to weeding my flower beds and my garden, I prefer to do it the old-fashioned way and pull them up by hand. I am a gardener after all, pulling weeds is a hobby.
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