stay safe: horticultural vinegar and how to read any pesticide label, with noelle orloff

IN A RECENT industry newsletter, I saw a link to a story about the herbicide called horticultural vinegar, and clicked on it. And then, realizing how little I knew about this product that I see prominently displayed in every garden center I visit, I wrote to the story’s authors at Montana State University to ask them to tell me more.

In our subsequent series of conversations, I learned a lot about these high-concentration vinegars, and most of all about reading all product labels to be a smarter, safer consumer–whether the products are natural, organic, or synthetic.

My guest Noelle Orloff is the Weed and Invasive Plant Identification Diagnostician at Montana State’s Schutter Diagnostic Lab, where she identifies plants submitted by growers, ranchers and homeowners, and provides management recommendations if needed. She’s also a passionate home gardener, and I’m so glad to continue our conversation.

Read along as you listen to the Aug. 9, 2021 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on Apple Podcasts (iTunes) or Spotify or Stitcher (and browse my archive of podcasts here).


Margaret Roach: In the weeks since I virtually met you and your colleague Jane Mangold, I find myself checking the Montana weather to see how you’re faring, because boy, you must be some intrepid gardener and have some very tough plants out there.

Noelle Orloff: Margaret, I am an intrepid gardener, and my plants are really tough. I do a lot of native plant gardening in my own personal gardening life, and they’re doing great, even though it’s been 90 degrees most of the summer.

Margaret: Yes. And you’re a little short on rain, too, I think out there.

Noelle: Oh indeed. It’s a really horrible drought in Montana this year. Yes.

Margaret: Well, I admire your courage [laughter]. We’re spoiled here, I guess still. And it’s havoc now and again, but it’s not like that.

So in your professional life, tell us just briefly a little bit kind of what you do and again, with your colleague Jane Mangold, there at Montana State, and sort of also what the word “weed” means in your world.

Noelle: Great question, Margaret. So the Schutter Diagnostic Lab is a service offered through Montana State University Extension. And we’re a plant clinic that helps people figure out either what organism is that they have a question about, or what’s wrong with their plant. And I work with a whole team of people from plant disease experts to insect and arthropod experts.

But my particular expertise in that lab is weed science. So I work with people on plant identification and also how to manage unwanted plants. And most of our clients are our local extension agents and the counties and reservations across Montana. And I also work directly with growers and homeowners and pesticide applicators, and all kinds of people like that.

So a lot of what I do is work with people about plants they don’t want. And to me, Margaret that’s what a weed is. It’s any plant that somebody doesn’t want for any reason could be considered a weed.

Margaret: And you and Jane work a lot with large landholders, too. So ranchers and other groups that may have large tracks of land, and they may be dealing with very serious invasive plants where you can’t hand-weed it out, right?

Noelle: Absolutely. Yes. Jane and I both work with clients like that. In Montana, a lot of ranchers are working with big landscapes, and public land agencies. People like that are working with large landscapes. And when they’re working with invasive species or noxious weeds or regulated plants in Montana that have impacts to biodiversity and livestock forage and wildlife forage and things like that, those plants are important to control. And also they’re on those large landscapes, where hand weeding is not going to cut it.

Margaret: Right. Right. So you try to help them come up with the least-toxic and most effective solution that’s geared to what they’re facing and the conditions and all that kind of good stuff.

Noelle: Yes, that’s exactly what we do. Everybody we work with, we work with them on kind of an Integrated Pest Management approach. So kind of taking all of the available tools together and seeing what might be most effective from grazing to mechanical control, like mowing, to herbicides—putting all those tools together and coming up with the least-toxic and just kind of the least non-target impacts as well to organisms that people want to have out there.

Margaret: So for those people who haven’t seen it, you and I and Jane collaborated on a recent story on the subject of herbicides, and especially horticultural vinegar, for my “New York Times” garden column. And I’m eager to share kind of what we talked about.

And it’s funny, because when I first approached you guys I had the one question and then it just turned into like, we were kind of collaboratively exploring this subject. I was like, “Why is there this stuff on the shelf in my garden center, that’s not labeled in herbicide, but it’s among all the other herbicides? And it’s this vinegar and it’s like 20 or 30 percent acidic acid?”

And then you guys said, you saw that there in your store, too. And we got into this whole conversation about labels and whatever.

But before we get to that, I suspect you hear a lot about people’s home remedies like I do as a garden writer [laughter]. And those are pesticides, too, if they use them on a pest, like a weed, right? They’re an herbicide. Right?

Noelle: Margaret, I think that’s a great point. I think people they hear the word pesticide and it gets such a bad rap, but really a pesticide is just any substance that we’re applying to a pest that we’re trying to control. So to me, something that someone’s mixing up from their cabinet made up of some household vinegar, some salt and some dish soap is a pesticide.

Margaret: Right. And people don’t understand that pesticide can mean against an insect, against an unwanted plant, against an animal. I mean, it can be against bacteria. So herbicide is one sort of category within pesticides.

Noelle: Exactly. Yeah. Yes, Yes. Yes. Just that a pesticide use to control weeds is an herbicide.

Margaret: Yeah. And so I’ve been an organic gardener for a long time and I don’t really use them. And so, I see people make their own home remedies. And so you mentioned one in the story, that someone told you they were putting bleach on some plants or something. And I was like, “Oh my goodness.”

So let’s talk about the vinegar—quote, unquote vinegar—because I mean, it’s not like the vinegar in your kitchen pantry, is it?

Noelle: Horticultural vinegar isn’t like the vinegar in your home pantry. And I think that the main difference is the concentration of the active ingredient. So the active ingredient—the part of the substance that actually impacts a plant—the active ingredient whether you’re using household vinegar to spray on a weed or horticultural vinegar is acetic acid. And in household vinegar the concentration is going to be about 5 percent, usually. And with horticultural vinegar, it could be more like 20 or 30 percent.

So that’s kind of the difference, the horticultural vinegar you’re going to grab them on the shelf at your garden center is going to be more that 20 or 30 percent concentration.

Margaret: Right. And with your blog post that I read last month that got me to contact you, I think it started with something like: “Does horticultural vinegar kill weeds? Well, it depends.” Right?

Noelle: Yes. It does depend, and kind of with any herbicide, including horticultural vinegar, there are ways to use it that are going to be more effective or less effective, right? So with horticultural vinegar, I think there’s a few main things to keep in mind for its efficacy—how well it’s going to control weeds.

One is how big the weed is. So if you’ve got a teeny little weed, it’s going to work better than a big weed. The weather can make a big difference. Acetic acid or horticultural vinegar is going to work better when it’s hot outside than when it’s cool outside. And it’s going to work better, probably, on annual weeds. So little weeds with little root systems compared to perennial weeds that might have a bigger root system, because it just burns down the topgrowth. It’s a contact herbicide, and it’s not going to move into the roots to affect those at all. So just a few examples. [Above, horticultural vinegar works best on annual weeds with only a few true leaves. Noelle Orloff photo.]

Margaret: So basically when you say burndown or contact herbicide, it means that, and again: This could be a home remedy. This could be an organic substance. And by the way, some of the acidic acid, some of the horticultural vinegars are labeled as organic and some are not. And oh boy, that’s a whole other can of worms [laughter].

Noelle: It sure is.

Margaret: Yeah. Because if they’re not registered as an herbicide with the EPA, a particular brand and concentration, it’s not technically an herbicide. And oh my goodness, it’s very confusing. But: So with a burndown herbicide, the tissue that it comes into contact with is what it’s going to burn down—that’s what it’s going to destroy. So, as you said, it’s not ingested by the plant and metabolized by the plant, and so it’s not systemic.

Noelle: Exactly. It doesn’t move in the plant at all. It just affects exactly the part that it touches.

Margaret: Right. So when I see some seedlings in the driveway or cracks in the pavement that have a couple of leaves that have just emerged, some self-sown, unwanted annual weeds, maybe it’s good for that, but it’s not something that would be good on large plants or well-established plants.

Noelle: Yeah. It wouldn’t be as effective on established, larger plants. And another place where it might not be the right choice is in your lawn. So one thing about acetic acid is that it’s non-selective, meaning that it impacts any kind of plant. So if you spray a little weed that’s growing in your lawn grass, it’s going to hurt your lawn, too. So that’s another thing to kind of think that’s-

Margaret: Right. So it’s non-selective, it’s kind of indiscriminate.

Noelle: Yes.

Margaret: Yes. So despite the fact that some of the most popular brands of horticultural vinegar that is being marketed everywhere from online, in the big box stores, in the garden centers, in concentrations from 20 to 30 to even 45 percent, I’ve seen for sale online. It may have a dandelion, a picture of a dandelion, on the bottle. But that doesn’t mean that you should, again, like what you just said, Noelle, that you can go zapping all those dandelions one by one in your lawn, because you’re going to make a bunch of really big brown spots. Right?

Noelle: That’s true. Yes. That’s true. And you know, maybe your grass will grow out of it. But it’s going to make some unsightly brown patches probably for sure.

Margaret: So figuring out what the right herbicide is, if we want to use one—and again, an herbicide can even be your home remedy, or it can be the horticultural vinegar. It can be labeled organic or natural or not. Figuring out the right one, and using it at the right time and in the right way on the right plant at the right life stage, that’s kind of the formula for success.

But what I want to know is, and we talked about this in the Times story: We could all go up and down the cracks in the pavement, on our front walk and the driveway and whatever. But even if we burn them down, what if there’s these just brown things sitting there [above]? Do I really want to spend the rest of the season walking up the path past these disfigured plants, or shouldn’t I have just pulled them in the first place?

So it’s also sort of figuring out strategically what’s going to work, and really be an asset, even if it’s with one of these more natural seeming substances, like the horticultural vinegar. [Above, pigweed in the cracks a few hours after applying horticultural vinegar; Noelle Orloff photo.]

Noelle: That’s so true, Margaret. I think a lot of times working with people on weeds and stuff, I like to ask people kind of what their objective is. What do you want to achieve here? And if your objective is to just get rid of the weed right then, reaching down and pulling it out might be the best way to do it.

But if you’ve got a ton of some weed in your sidewalk crack that you’re just not going to be able to get to all of them. I certainly have some of that in my sidewalk cracks [laughter]. It would be impossible to kill all the prostrate knotweed in my sidewalk cracks by hand pulling—maybe a horticultural vinegar would be a good choice then to limit seed production for next year. So it just depends what your objectives are.

Margaret: Right. Near me, I asked one of the employees of local small high-end landscaping firm that does a lot of garden installations and care here. And most of their clients.. Their practice is organic. They do use some organic products and so forth. But I said, do you use this sort of horticultural vinegar? And they said, “Oh yes, we use it on clients’ driveways.”

And I can sort of understand that because where I live, at least, a lot of us have gravel drives and so forth and not asphalt. And you get millions of little tiny weeds at the same time. And so I said, the next question, which is what I want to talk about with you next: safety.

I said, “So do you wear an N95 mask and a face shield and safety goggles and long sleeves and pants and socks and shoes and waterproof gloves? And do you follow the full safety precaution?” Because what does it say on that label for these strong vinegars? It says, “DANGER,” doesn’t it, Noelle?

Noelle: It does say danger. And right now on my computer screen. I have pulled up a 20 percent acetic acid product that’s labeled as an herbicide. And everything you just said is what’s listed as the personal protective equipment on that label. So yeah, that danger warning on there is because this concentration of acetic acid can cause irreversible eye damage.

And so reading the product label and making sure that you’re using the personal protective equipment is super-important, even if you’re using an herbicide labeled as organic. It’s still really important to read the label and make sure that you’re taking the safety precautions that you need to be taking.

Margaret: Right. Because organic doesn’t equal benign or safe necessarily.

Noelle: It does not. The acetic acid may be naturally derived, right? It’s not a synthetic pesticide. And that’s what it means. But it can still have human health impacts. And in this case, it’s potentially to your eyes and skin.

Margaret: It can cause very serious skin burns, and apparently inhaling the fumes can irritate the lungs as well. And that’s why, like you said, that the danger word and those instructions that are on a product that says danger—those as they call them signal words on the label—that’s meant to tell us about the potential acute toxicity. It’s not a thing about the environmental impact, or whatever; it’s not about long-term anything. It’s about danger, right then, acute toxicity to the human who’s using it. Yes?

Noelle: Yes. You’re right. And paying attention to that is so important, like I said, whether you’re using an organic or a synthetic pesticide. So glad you brought that up.

Margaret: It’s very confusing because, again, it’s the labeling laws, I guess. They have these signal words, danger being the most extreme one, the most “dangerous” one. And we don’t as consumers, uneducated, not like you a weed scientist. We don’t know what the language is. So what else on a label should we be looking for? And this is a label for any kind of pesticide that we’re considering using, herbicide or otherwise, natural or organic or otherwise. What else is on there that we should be zeroing in on do you think?

Noelle: Most pesticides will have the site where the pesticide is allowed to be applied. So some will be agricultural land, and some will be residential areas, things like that. I think that’s really important, especially for a lot of synthetic herbicides. Yeah. It can get really interesting if you start applying agricultural herbicides to home areas.

Margaret: Yeah, let’s not do that [laughter].

Noelle: Let’s not do that. You see a lot of tree injury from that kind of stuff in Montana, anyway. So the site of application is really important. There’s always a little first-aid section that I think is good to skim over as you’re getting ready to use it.

On these herbicides, these substances labeled as herbicide, at least, there will be a personal protective equipment section, read that, adhere to it. I see people out there spraying weeds in flip-flops, and I don’t think there’s very many herbicide labels that tell you that that’s O.K. So the acetic acid one says shoes plus socks. So listen to that kind of stuff.

And then there will be a section about environmental hazards that I think as thoughtful weed managers we’re interested to look at. And then hopefully—not every label is exactly the same in this way—but a lot of times there’ll be really great information on there about which weeds can be controlled well, and maybe even some ideas about weather conditions that are good to apply a specific pesticide in, and things like that. So labels can have a lot of really great information on there and just vital information, like personal protective equipment, right?

Margaret: Just to drive that point home for people, because again, it says vinegar, there may be some dandelion on the label, you’re thinking, “Oh, this is going to be just great.” And I see the comments and some of the big box online stores, where people rate the product and they give it five stars, and they say, “I felt so good because I don’t have to worry about my kids or my dog being harmed by it.”

And again, these concentrated acetic acid products you are meant to be wearing, I’m just going to repeat it: face shield, N95 and safety glasses and long sleeves and long pants and waterproof gloves. And when you take those gloves off—you shouldn’t take those gloves off until you rinse the outside of the gloves, and this is serious business people. So we’re not “ready, shoot, aiming” with this stuff, are we?

Noelle: We’re not, I think that’s a great point about thinking about the people, the pets and other people that are around after you apply the pesticide, this acetic acid product that I’m looking at here has some kind of use requirements, which are kind of describing how workers need to be protected if they’re using this in an agricultural situation.

And in there, it says don’t allow workers to enter the area where it’s been used for 48 hours without protective equipment.

Margaret: I know.

Noelle: And certainly I would wait until it had dried fully before having any pets, any children in that area.

And I know sometimes these labels can be kind of esoteric. The print is small. There’s a lot of information in there that people aren’t used to looking at.

If you’re looking at a pesticide label, or even if you’re thinking about using some other substance in your garden as a pesticide, and you have a question about how toxic it is or how dangerous it is, get in touch with somebody who knows about that stuff. I would just plug your local extension service for that. I think, we’ve got pesticide-safety experts throughout the country and the extension service. And I think if you have any questions about stuff like this, reaching out to those folks is a great idea.

Margaret: Well, Noelle Orloff I’m glad to speak to you about this. And I learned a lot, as I said, in our collaboration on the Times story, and I’m going to give some links to how people can find out how to find the expert people you just mentioned, at their extension and so forth. And I hope I’ll talk to you again soon.

Noelle: Thanks, Margaret. It’s been so fun and interesting and informative getting to talk to you about this stuff and dig into it a little bit more.

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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 11th year in March 2020. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the Aug. 9, 2021 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).

  1. Heather Maxson says:

    I just read the article on the DIY herbicides just in time, as I was about to merrily start spraying weeds in my gravel driveway. If we have too many to hand pull, what do you recommend? Thank you!)

  2. Crew Mom says:

    Great post and NYT article as always, Margaret, thank you. One of the struggles we have trying to be responsible users of modest amounts of herbicide is application. The problem areas we have (driveway, road edges) are too large to manage with the little hand held spray bottles, and every single larger sprayer marketed to home gardeners we’ve tried is absolute junk, failing after only a handful of uses, including some from companies who market to the trade and should be doing better (looking at you, AMLeonard). I’ve never seen the sprayer in your photo above. Would you be willing to share some information about it, or are there some you can recommend? Thanks so much.

  3. Catherine A Mitchell says:

    Good to know about pesticides and herbicides. Reading all about the labels and even if you make you own it’s still a pesticide. Thank you for this blog. I’ve learned so much. Glad that I have subscribed to through my garden club here in Missouri.

  4. Jenn L says:

    I’m so glad you talked about this subject! I’m on numerous gardening groups and there are so much misinformation out there! I am constantly cringing when that happens.

    I would love it if you could talk about battling Japanese knotweed. The MA and CT extension office recommended specific herbicide target management but the herbicide has gotten such bad wrap uneducated folks are telling people not to use it, and knotweed just continues to take over. There are specific time you have to apply said herbicide. I think if someone like you talk about it on your podcast and interview the expert, that would be so helpful to get the correct information out there

  5. Lynda Pollock says:

    Such a good reminder! As a Master Gardener I tell my neighbors when asked that whatever they choose they need to read and follow safety precautions. I always suggest a specific product that’s been tested and shown effective as opposed to stuff mixed up in the kitchen.

  6. Jane Sherrott says:

    I will never use hort vinegar

    I sprayed concentrated hort vinegar on a large concrete fountain, scrubbed it then filled it with water and let it run off to get rid of green gunge. I was horrified by what happened- the runoff (now the concentrated hort vinegar quite well diluted) ran onto the grass and caused worms to come writhing to the surface of the grass. I picked up the poor worms and put them on wet dirt then sprayed them gently but they looked like they were writhing in pain. I imagine the hort vinegar not only harms the worms and insects in the soil, but also the bacteria and fungi that are so critical for soil health.

    Learn to live with some weeds, chop and drop mulch to stop seed germination, use a knife to dig out weeds if you must- taking the time to weed naturally connects you to your garden’s beauty and helps develop a healthy ecosystem.

    1. MB Whitcomb says:

      True to my experience too. Your point on hand weeding is eloquent and spot-on. I have 1200 feet of road and ditch for my one acre, and, while I love hand weeding, can’t do it all by hand any more. We use miniscule amounts on individual plants only, and plant native plants immediately…but along the road, the machines disturb it regularly, and introduce new noxious and physically harmful weeds like wild parsnip.

  7. Mary says:

    I love when you delve into the day to day maintenance items of gardening. A friend uses the horticultural vinegar and never mentioned the care that needs to be taken when using it. I also doubt they realize that the product does not get into the roots. Lots of good points about what to look for on labels. I have not used any herbicide or pesticide in many years, but I am ready to find something that works on bindweed.

  8. Michelle says:

    Great article. I never use herbicide anywhere. I hand pull as much as possible or use a crevice tool. A good remedy for cracks in walkways and driveways is to fill them with polymeric sand. It binds together and prevents weeds from germinating. Looks good and saves weeding time. Very easy to apply.

  9. Thanks for this…I ran some trials in my gardens, and found, on a heavily weeded gravel driveway, that it killed things down, but a slime mold (or something blacky-green and VERY slipprey) grew in large amounts…this made the driveway a hazard. In another trial, I did not see a frog, and it literally screamed. It burns skin too. Nope. There is no better “selective” herbicide than the human eyes and hands. Machines usually give advantages to things that grow by stolons and weeds in seed, effectively distributing them. That said, we DO have a biological stew of invasive plant species, and I totally oppose a BAN on commercial herbicides. They are a “last resort” tool. We have many “tools” that are toxic or carcinogenic…like chemotherapy drugs and even sawdust (ACTUALLY carcinogenic, not “probably” as Round-up is considered). We don’t scream and yell for the total elimination of these things. Petroleum is one of the most toxic things around, but no one is abandoning their cars or toys. So let’s keep things in perspective. If Round-up is the fastest way to get rid of plants that out-compete native plants, I support it…too much of their habitat is gone and they can’t grow where they are native, I am for it. I don’t say this lightly. I have spent five months now, weeding everything by hand MORE than full time, on one property trying to get back to native balance…made a little progress, but only if I spend the rest of my life on my hands and knees. Been working with invasive plants for more than 30 years…if you think the other political party is a bad adversary, try invasive plants…we need to stand together against this problem…the IUCN points to invasive species being responsible for more extinctions than even climate change…both potentiate the other, and we are only paying attention to climate change…the biggest oversight that will compromise the health of our future generations and biodiversity. Great piece, Margaret, totally love you. If you ever want to vacate as our guest in Cape Breton in a house by the Bras D’Or Lake, look me up, we’d treat you like royalty. Such fine work.

  10. Wendy Wallwork says:

    Cannot be stressed enough how potentially harmful ” horticultural’ vinegar can be.

    Household white vinegar can be used full strength on small weeds in pavement cracks, early, often & on a hot day.

  11. Woozie Wikfors says:

    Margaret, a number of times in this article you referred to the active ingredient in vinegar as “acidic” acid. Please correct this.

  12. Kathy Pile says:

    Being an avid gardener it’s important to be aware of herbicides and pest control. I try to stay organic and use household items to help me with pests in my garden. Dish soap in a spray bottle with water works well for most of my issues. Thank you for the insights.

  13. Kathie says:

    Appreciate the information and REALLY appreciate that you reposting it from your NYTimes article, which I can’t read until another month passes because of the firewall and no subscription.

  14. Ray Benton says:

    At the time this podcast aired, and the NYT article came out, I put together a one-pager about using vinegar which I shared with family and friends. One thing not mentioned in the podcast is that vinegar of the 20% to 30% variety, when applied to weeds also impacts the soil. The most important soil characteristic is pH and vinegar changes the pH of the soil. Not only are the living plants burned and (in the good sense) killed but the vinegar makes it difficult for them to return. If that is a problem, because maybe you want to plant something where you treated it with vinegar, you can re-treat the soil with an alkaline base. It will return to a more neutral pH, which will allow for more efficient cellular cation transfer—whatever that means. The base used should be determined by what nutrients the plants need for best growth. That is all well and good. I just want to kill the weeds and on a gravel walkway! If the vinegar inhibits weed growth during the rest of the summer, that is okay with me. It will dissipate in 6 to 12 months and have to be retreated next year. And to reiterate what the podcast said, be careful with the fumes and do not get any of the vinegar on yourself. People tend to be less careful with vinegar, because they are used to applying it to the salads and eating it, but that industrial strength stuff is toxic. Think of it not as vinegar but as acetic acid, with the emphasis on ACID.

  15. Linda Duda says:

    When it comes to any pesticides and herbicides the first thing stressed in the Master Gardener program is “the label is the law”. So important to know this.

  16. Ann says:

    Boiling water and pouring it in the cracks of my driveway and sidewalk has worked great for me. You just stay on top of it. 2-3x per summer. And I have found just digging the weeds out properly lasts longer.

  17. Jeanne Mann says:

    I cannot thank you enough for your article about 20% vinegar which I have been using really in my small backyard garden to keep encroaching vines from the neighbors from invading over my fence. I have been doing it with no protection. I had no idea that it was dangerous and I think you’ve changed my life for which I thank you

    1. margaret says:

      Jeanne, it means a lot to me that you took time to comment. This is the stuff that gives me the shivers — how little we consumers really know about so many household products we use. Yikes, right? Glad to spread the word.

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