do home remedies for weeds or garden pests work? ask jeff gillman
GARDENING MAY BE part art and part science, but when it comes to plant health, and especially to preventing and combating pest and disease, I vote for going heavy on the science, and not getting too artistic. So does Dr. Jeff Gillman, the director of University of North Carolina at Charlotte’s Botanical Gardens, who helped me evaluate some of the internet’s recent popular home-remedies for herbicides, disease and pest control (like the iffy combo above).
I’m a longtime organic gardener, meaning no lover of chemical “answers” to problems, but I’m also no lover of the endless and often-wacky home remedies that I read about year after year.
Some home remedies do work, but some are not just ineffective, but also dangerous, sometimes as dangerous as chemicals.
I was interested to read an open letter in summer 2015 to “Consumer Reports” written by Jeff, a former Associate Professor of Horticultural Science at University of Minnesota, who has a masters in entomology and PhD in horticulture, plus 20 years of practical and research experience with plants. He’s the author of “The Truth About Garden Remedies” and “The Truth about Organic Gardening,” and most recently “Decoding Gardening Advice,” and one collaborator on the popular Facebook page The Garden Professors and The Garden Professors dot com website.
Does vinegar-Epsom salts-soap kill weeds? And what about clove oil instead of Roundup? Can you home-brew a deer deterrent? We talked about all that and more on the July 27, 2015 edition of my public-radio show. Read along as you listen using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
my q&a on home remedies, with jeff gillman
Q. Congratulations on the new position. From a long-ago visit, I seem to recall the UNC-Charlotte gardens as having lots of carnivorous and bog plants.
A. The former director, Dr. Larry Mellichamp, was a carnivorous plant specialist so we are loaded with carnivorous plants. In fact, we just finished having a Titan Arum bloom [timelapse video above], which was absolutely wonderful…
Q. And stinky! [Laughter.]
A. And stinky. It smelled pretty bad, but it was magnificent. I had never seen one before.
Q. I have only seen them on the RHS website or news reports from Kew, for instance, but have never seen (or smelled) one in person.
A. You need to have that experience. Your eyes will delight, and your nose will…well, never mind what your nose will do.
Q. Foetid. To attract flies [and carrion beetles] as a pollinator, you need to stink, right?
A. Absolutely, and this one does.
Q. We won’t have the scratch-and-sniff here on the radio then.
Shall we start with this mixture that’s been going around the internet since spring, of vinegar and Epsom salts and soap, that claims to control weeds as well as Roundup? That’s one I know you mentioned in your open letter to “Consumer Reports.”
A. It’s not the one I stressed, but it is one I felt the need to deal with, because in their latest issue they actually published a letter from someone who asked if it worked as well as Roundup, and they said, “Oh, sure, it’s wonderful”—and I am paraphrasing. But the truth is that this mixture of vinegar, Epsom salts and soap first of all doesn’t work as well as Roundup, and second, it’s potentially damaging to your soil. So I really don’t understand why they are promoting it as strongly as they are.
Q. Potentially damaging to your soil because of the residual effect of pouring on Epsom salts, Epsom salts, Epsom salts—is that the issue? What happens?
A. One application of this certainly isn’t the end of the world. But Epsom salts is a type of salt [magnesium sulfate], and potentially after you add salt for a long period of time, what happens is that it will actually pull water out of the plant. There are certainly worse things: if you mixed sodium chloride with that vinegar, that would be worse for planting in the future. But this is still not what you would consider a “safe” remedy at all.
Q. Not to just use at will.
A. And then of course the other part is that it’s not going to work as well as Roundup, because this is a contact herbicide, or what we think of as a burn-down herbicide—it’s going to kill what it touches. It will burn down the top of the plant rapidly and it will look great, but it won’t kill the roots, so it will come right back.
Q. We should say right away: You’re not on the payroll of the folks who make Roundup [active ingredient: glyphosate], or advocating the use of chemicals. You’re talking about making the smartest decision in each situation for the safest, sanest, most-effective tactic—whatever that is.
A. I’d prefer that everybody go out there and dig up weeds.
Q. I am glad you said that, because we concur. Like you always say, “How about kneeling down and pull out some weeds?” [Laughter. Photo above: Margaret demonstrating her low-tech approach to weeding.]
A. Get yourself some exercise. You and I are on the same page. I don’t particularly like Roundup; I have to be honest. I see a purpose for it, and use it now and again, maybe every two or three years to take out some major weed. But if you think that this vinegar-Epsom salts solution works better, you’re fooling yourself.
Q. So what was the primary thing that got you roused to write to “Consumer Reports?” Was it the clove-oil treatment that’s also been circulating recently?
A. Yes, and clove oil can actually be purchased as an herbicide. You can buy a spray-on product composed of it. The thing is that it was written about as a safe alternative to Roundup, and the implication was that Roundup is unsafe. You’ve probably heard that the World Health Organization has called Roundup a “probably carcinogen.” I understand why they did that, but I wish “Consumer Reports” had talked about what a “probable carcinogen” is.
You’re calling Roundup a “probable carcinogen,” and that makes it scary, so let’s avoid Roundup. I have no problem at all with that. But then, they recommended clove oil.
Clove oil is eugenol—that’s the chemical—and look up eugenol and you’ll find all kinds of problems. You’ll even find a story on how it even almost killed a 2-year-old, just 5 to 10ml of it.
[Studies with rodents have demonstrated that eugenol could be carcinogenic, and companies that sell the product treat it that way. Read one eugenol-based product’s Material Safety Data Sheet and an MSDS from another manufacturer of eugenol, as examples. The National Toxicology Program study with rats and mice is here.]
If you’re going to recommend an organic solution, I think that’s wonderful. But let’s pick one that’s not as dangerous or even more dangerous than the thing you’re trying to replace.
Q. You’ve tested clove-oil products, not just read the scientific literature?
A. I read it in the scientific literature, of course, but I have also tested it side-by-side with Roundup.
A. It’s a quick-and-dirty experiment, and it would be better if I did a huge replication. But a few weeks ago I did the experiment and the clove oil did fine: It burned the tops of the plants. Roundup burned the tops, but over time also killed the roots. The clove oil did not. It’s another situation where the clove oil just didn’t work as well.
Q. In the “Consumer Reports” article, I think the claim was made that the clove oil would kill stumps of barberry and kudzu and such.
A. Now that’s crazy. We’re talking about a contact poison—in other words, it kills what it touches. If you put clove oil onto a cut stump, you’ll help to kill the top of that stump, but the roots are still healthy and even most of the stem is still going to be healthy.
Q. So “contact herbicide” on the one hand, and on the other end we have a “systemic herbicide.” Is that correct?
A. Correct, like a Roundup. It’s actually going to be taken up by the plant, and transferred to the root system.
Q. So it’s as if it’s metabolized?
A. When you cut down to a stump, and you have some of the plant’s vascular tissues exposed, and put some Roundup on it, it will get taken up by the vascular tissue and transferred to the roots, as long as the cut’s relatively fresh. I have to say: Roundup is not labeled for that, and I don’t recommend that; I don’t recommend anything that’s not on the label.
Again: My preference is digging up the stumps. I think that’s a much better choice. I don’t want to go on record as saying I support using a chemical for that. Spend an extra couple of minutes, and dig out the stump.
Q. And if it’s large enough and troublesome enough–you might need mechanical help. There are also machines, mechanical tools, that could help you remove the roots. I have sometimes hired someone to remove them in a mechanical way—beyond my capability maybe with my shovel, or mattock, but the machine is a non-toxic choice, too.
Q. It’s very important for people, when choosing an herbicide, whether it’s said to be “safe” and “natural” or what, to know whether it’s a contact herbicide or a systemic herbicide. On the labels it also states if something is a “selective” herbicide—what does that mean?
A. A selective herbicide means it will kill certain weeds, or certain types of plants, but not others. The most common type of selective that you have is an herbicide that will kill broadleaf weeds but not grasses. So the herbicide that some people use in their lawns—the weed-and-feed that will kill dandelions or clover, for instance. That’s 2,4-D, and it has been around since the 1940s; it was a World War II top secret.
A. It really was. It will knock out your broadleaf weeds while leaving your grasses. It was heavily used in corn, because corn’s a grass.
Q. So it’s selective. And the others are what, non-selective, or…?
A. Broad-spectrum, and Roundup is broad-spectrum, tremendously broad-spectrum.
Q. So that’s the other thing that we’re looking for if we’re reading a label, and even considering using it.
A. There are a couple of things to look at on the label: I think the first one is the safety of the product. Always on a label you will find what’s known as the “signal word,” and that is either caution, warning or danger. I don’t think there’s ever a reason to use a product whose signal word is warning or danger. With anything stronger than a caution label, you need a professional.
Q. Last time we spoke we talked about “vinegar,” and I am putting it in quotes because people are buying “horticultural vinegar,” which I think is a euphemism, which is 20 percent acetic acid. This is not something I should be exposing myself to out there in my shorts and without proper gear on. This is a strong chemical.
A. Yes, it’s 20 percent acetic acid—and potentially stronger. I told you the story about how I accidentally killed a poor frog.
You just open up the bottle—and of course the first thing I did was sniff it, which was the dumbest thing I could do. It bring water to your eyes, and if it gets in your eye it will burn your cornea.
Q. It will burn skin, and again: If you really read the label, and don’t just go on the internet to purchase some by mail, where it says, “Yeah! Kills everything! Natural! Woo-hoo!” and has a picture of butterflies on the label to boot—if you really read the legally required small print it explains that you are supposed to wear full protection as if you are a licensed applicator, a professional.
It’s being bought off the shelf, and shipped to people all over the place—and it’s dangerous. [Its signal word: danger.]
A. People are thinking of it as natural and therefore safe. There’s a term for it that we should probably be using, and that’s greenwashing.
Q. So we’ve talked about 2015’s popular home remedy that’s not so effective, vinegar and Epsom salt and soap; we’ve talked about the strong vinegar; about clove oil. What about some disease-control home remedies—shifting to disease remedies. Are there some that do work?
A. There are a few that do work. Let me run through some really popular ones for you:
Number 1 that I see is baking soda, and it actually can work. Since the 1920s we’ve known that a baking-soda spray really can help control powdery mildew. A baking soda spray varies, but usually it’s a Tablespoon or 2 of baking soda in a gallon of water, plus a little bit of soap.
Here’s the thing, though: A couple of years after research showed that this spray could control powdery mildew, research then showed that it didn’t control blackspot. So all these people are using it to control blackspot, and it really doesn’t work on that. On powdery mildew—yes, go for it.
Q. And not after the plant is entirely coated in mildew—we don’t start then, right? Early intervention, yes?
A. All of these home remedies are not what we call curative; they’re all preventative. You actually need to start it even before you start to notice the powdery mildew. That’s one thing on the downside about home remedies. By the time you see it, it’s not too late, but almost.
Q. What’s Number 2 on the hit parade of home remedies that do work?
A. The one I think the most of—though it’s not perfect—is milk. One part whole milk, two parts water. I say whole milk because that’s what I have tested. Other people say powdered milk or skim milk, 1 percent—they all seem to work fine. My experience is with whole milk, so that’s what I recommend. Again: You have to start applying it [weekly] before you have problems.
Q. What are we using it for in this case?
A. It works well for blackspot, and reasonably well for powdery mildew. Those are the only two things I tried it against. The reason they think it works is that it contains a protein called lactoferrin, and lactoferrin is an anti-microbial.
Q. So there is chemistry involved in all of these—it’s chemistry, not magic. [Laughter.]
A. Exactly, and so often when we hear people promoting home cures, and organics, they’re saying, “There are no chemicals.” Nature’s made up of chemicals. And nature can give us some wonderful chemicals to use—but we just have to be thoughtful about using them in a proper way.
Even flame weeding is using a chemical [propane].
Q. A lot of organic farmers I know are doing it, and it can be very effective, but it does have its downsides and dangers. It’s a little scary.
A. I burned all the hairs off my hand once. I actually like it, but you’ve got to be careful—it’s fire. And don’t do it on a dry day, please.
Q. What about homemade animal repellents (she says—not that she’s overrun with every animal under the sun in her garden). [Laughter.]
A. There are a actually a number that are pretty good. The one that I recommend, which we’ve used in field plots (not for research, exactly, but I had a graduate student use it to repel deer and it worked pretty well): about 5 eggs or so in a gallon of water.
Q. Blend it up so it’s like it’s emulsified?
A. Yes, you blend it up; some people like to add a little soap. The best animal repellents out there, especially for deer, include some quantity of eggs. On the container it will say, “putrescent egg solids.”
Q. That’s another nice word: We started the conversation with “foetid,” so now we’re at “putrescent.”
A. Doesn’t smell as bad as the Titan Arum, but it still smells pretty bad.
Q. So we could blend up 4 or 5 eggs, in some water and use it as a spray. Do we let it fester first?
A. You don’t need to let it rot first. It’s one I don’t suggest spraying on your veggies, because they won’t smell good.
Q. More for use in the shrubbery and so forth, where you have browsing.
A. It’s a good winter spray. One of the advantages to the commercial sprays over home-brewed, is that they include ingredients to help the spray stay on the plant for longer.
Q. Are those surfactants?
A. Yes, surfactants—and they’re basically soaps.
Q. Thanks, Jeff.
visiting u.n.c.-charlotte botanical gardens
THE U.N.C.-CHARLOTTE Botanical Gardens, with 10 acres of outdoor gardens plus conservatory collections, is open daily during daylight hours, with greenhouses open 10-3 Monday to Saturday and 1-4 on Sunday. Details are at this link. A diversity of seasonal highlights in the collection range from native plants to bog plants (above), camellias to orchids, carnivorous plants, desert plants and more.
prefer the podcast version of the show?
MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. 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 July 27, 2015 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
enter to win the books
Do you have a weed-control “secret,” or some other homebrew solution to weeds or other garden challenges. Or do you rely on store-bought products or some other tactical approach?
As you know, I’m old-fashioned: pulling weeds, and hand-picking pests (like Japanese beetles and cabbage worms), and generally relying on extra-careful “housekeeping” (especially in fall, in the vegetable garden) and lots of mulch to keep things together.
I’ll draw two random winners after entries close at midnight on Sunday, August 2, 2015. Another chance to win! I’ll draw another random winner after entries close at midnight Sunday, April 24, 2016. US and Canada only. Good luck to all.