do home remedies for weeds or garden pests work? ask jeff gillman

questionable herbicide home remedyGARDENING 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.

gillman booksI 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.

margaret weeding 2Q. 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.

by Jeff GillmanQ. I always love seeing your photos of the test plots you sort of “rope off” of the same plants in the same bed, side by side, and each square is treated differently [above].

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.

A. Yes.

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.

Q. [Laughter.]

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.

eggs and baking sodaQ. 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

pitcher-plants-tlmTHE 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

gillman booksI’LL SEND A COPY OF one of Jeff Gillman’s books to each of two lucky winners. Enter by answering this question in the comment box at the very bottom of the page, below the last reader comment:

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.

  1. Kat says:

    Please count me in!! I’d love to find something I felt comfortable using. I usually pull, pick and pluck by hand. Thanks for the help!!

  2. Beth says:


    Any recommendations for removing Bishop Weed? I am not a Roundup fan but the house we just bought has an old perennial bed taken over by the Bishop Weed and it must be removed. Thanks!

    1. margaret says:

      This is a tough one, Beth. The Plant Conservation Alliance has these recommendations (from manual to chemical) that are most effective, but it will take time. A friend when he bought his house years ago took an entire year to eradicate it before considering planting anything new. Spring is the time to hammer it as it emerges and deplete its energy…read the factsheet and see how, but again: don’t expect instant results.

  3. Terri Moreno says:

    Thanks for clearing up some of the nonsense out there. Unfortunately, a newer solution to gardening ills seems to crop constantly and we are all looking for the quick fix, both garden wise and health wise.

  4. Judy Walther says:

    My garden now is small enough now that I hand weed…I find it satisfying. In the past I have used Roundup esp for bermuda grass running. My main problem is squirrels. I recently read to hang red Christmas balls in the tomatoes to confuse them so I bought some at a tag sale and can’t wait to try it!

  5. Chris says:

    I hand pick and hand weed, unless they get out of hand. My neighbors don’t appreciate a front yard half weeded. :)

  6. Mary Kay says:

    Hi. Any suggestions for preventing racoons from esting new growth on vines in pots on our deck? Thank you. Mary Kay

  7. Liz Davey says:

    Hand weeding is my choice except for my brick patio which I spray with 10% vingear a couple times each summer, My main pest is chipmonks in the strawberries. Grrrrrr! I want some too and they are greedy.

  8. marla says:

    Raised beds, weeding vigorously at the start seems to keep the garden pretty weed free.
    Creeping charlie in the flower beds is a headache, but at least it pulls up easily.

  9. erin says:

    I would love to have a safe answer for crabgrass. My husband are in discussion about this on our suburban lawn around our little children. We pull and shovel mostly. I did find success with apple cider vinegar in an open container against tomato-chomping grasshoppers.

  10. ginger says:

    I have used Roundup on fence lines as I have a 20 acre farm. I now weed wack all the lines – not an easy time but there isn’t an easy alternative.

  11. Anne Sikkema says:

    I actually prefer hand weeding now that I have mulched everything! It give me a chance to really look at the plants and soil, give them some verbal encouragement and say hello to the worms. If you mulch well and stay on top of weeding for a couple of years, you will find that you need to spend less and less time weeding. I do 3 sweeps a year. One in the spring, one midsummer and one in the fall, yes before I put them to bed….I leave dead/dying perennials as they are, but I do weed. I live in a small City and except for the house and garage, my lot is entirely in gardens. No grass! .the other trick….if you see any weeds in flower…stop and get rid of the plant. Probably the hardest time for me is spring. Still hard to identify some baby weeds from baby perennials. Have learned to step back and wait until they are better formed and I know which is which….Another hard learned gardening lesson. ;)

  12. Audrey Ostrom says:

    Slugs love primulas quickly decimating leaves and flowers . I put my eggshells into one of those fairly tough bags our coffee is packed in, leaving the bag open to stop it bursting use a rolling pin to crush the shells as finely as possible. Use on the soil around the primulas or whatever plant is being chewed up. Using a spare blender the shells can be combined with water to make an even finer gritty mix which quickly disappears into the soil.

  13. Jane in CT says:

    I’ve been going after garlic mustard since we bought our house in 1999 by scuffing seedling drifts in spring; for larger plants, waiting till there’s been a soaking rain to loosen the soil to make pulling [actually teasing and bending the roots from the ground rather than yanking] easier. I look to see which way they’re leaning to reach the sun and wiggle them out in that direction.

    I’ll employ a 2-toed claw, also, or a straight weeder to loosen the area around it. I’ve used Roundup when there are too many to tackle at once to keep them from flowering and then go in later for their roots since they seem able to survive a Roundup shower.

    For bugs, and even slugs, I’ve had good results picking a bunch, pulverizing with water in a blender, letting it make a “tea,” straining to get out the bits, adding a touch of Dawn or Palmolive as a surfactant, and spraying it back on.

  14. Lois Williams says:

    Hand weed & mulch which takes a great deal of time on our two acres! We do use Roundup for poison ivy/oak. Deer are our biggest problem…all hostas are protected by netting and we try to plant only deer resistant shrubs & plants where netting isn’t possible. I do sneak in some tulips in the back of the beds close to the house and so far so good. We have tried coyote urine, battery operated zappers, hanging Irish Spring soap in the hydrangeas and numerous other remedies…most were not much that help.

  15. Jayne says:

    I found this incredibly interesting but not a bit helpful. I have a plot in an organic section of a community garden. Fewer and fewer people are interested in the organic section, with the restrictions placed . They think -Look what Sevin can do! ANd worse! I just attended a flower show with a conservation component and came away with an organic solution to weeds in our farm paths (the same one Jeff talks about) , and now that good information I was given….you are telling me to fah -get-about- it.

  16. Ferne says:

    A useful book…count me in Margaret. I just hand weed…being a very stubborn person. I will solarize eventually if that doesn’t work.

  17. Margaret Z. says:

    I like to mulch with pine straw. Pine straw works really well with keeping the soil cool and keeps the weeds down. I also use the just dig em up method too.

  18. joanne wallace says:

    On Cape Cod it’s all about hand weeding – I love my swoe for stand up weeding and I have a favorite hand weeder for ground level. Thank you for highlighting Mr. Gillman’s books.

  19. Carol says:

    I prefer to hand weed or pick and squash the bad bugs. I am lucky to not have anything I haven’t been able to control in this way. The only thing that made me resort to a chemical was the lily leaf beatle. I used Captain Jack’s Dead Brew. It has seemed to work. At least it brought the population down and I have continued to hand pick and kill with good results. I have found that just letting Mother Nature take charge, with a little helping hand, works best.

  20. Carol Edelman says:

    What a glorious day out in the gardens today! Happy to see everything growing, even the weeds. Well, sort of.


  21. ellen johnson says:

    hand weeding all the way – very peaceful (except when i’m digging out horsetail – the worst thing ever) and since our yard isn’t big enough to keep me busy, i volunteer weed at the local botanic garden.

    no magic tricks, just a ‘digger’ that gets under the roots

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