By the Plant Ladies, Christina Prime and Teri Chace
As I sit here on this mid-summer day, preparing to write my introduction to this month’s article, on, surprise, surprise, Japanese knotweed, I could maybe delude myself into thinking this may be the last year we have to write an updated version of our first article from July 2018, in which we brought to attention this scourge on our land, as well as so many other places.
The sad thing is, the more Japanese knotweed Facebook pages I join and the larger the infiltration into backyards and roadsides, I can foresee us not being done writing these articles anytime soon. I am not a prognosticator or anything like that but just nodding sage-like and believing that if we can help at least one person who’s fighting to eradicate this plant with our articles, we will continue to forge on. We have to believe we’ll make a difference, one year at a time.
My memory of this plant is from a very few weeks ago. I just happened to be doing some gardener doom-scrolling on the Japanese knotweed pages on Facebook when I read a lament from a sad person. She’d bought a house this past winter and lo and behold the early good days of spring arrived, she was checking out her property and was so disappointed, if not angry, to see the seller hadn’t noted in the real estate listing that she’d bought a well-established Japanese knotweed patch.
She came on the site to ask for help and insight. Most people gave her good advice and then I saw what made my stomach churn. A man denouncing [2%] glyphosate implicitly as not working and saying the only way to kill (yes, he literally said kill) this aggressive plant was to mow it. Oh my gosh!!! Teri and I have seen many people around here doing wrong things no matter what we say but when someone states such a blatant lie as fact, it just makes me want to pound my head into a wall. I am truly sad to know people are still saying downright lies as facts and, after almost 10 years, it hurts worse than ever.
Now please join my fellow plant lady as she reaches out to help sort out the real thing that works from the cover-ups. Hopefully this year she will lead at least one more person to not do the wrong thing and actually beat back knotweed for good.
Live and learn
The past few years of annual articles by us on this dastardly plant have not all been the same. Research has advanced. We’ve tried various things and learned a lot. The Facebook groups Chris mentions have started and grown to thousands of members (see list at the end of this article). News and information are spreading and the alarms are sounding!
Why fight this plant? Why try to kill it? Because it is greedy and rampant, and over time, takes over entire areas. Gardens and lawns. Habitats, ecosystems. Roadsides, fields. It does not share space or resources like soil, nutrients, and water. It is a selfish, dominating thug, excluding all other plants…permanently, unless somebody does something…something effective.
And heaven help you if it is close to your house, garage, or other building or pad, or encroaching on your unpaved or paved driveway or your garden. It can and does breach those things, damage, and even ruin them. True fact: in England, good luck getting a mortgage or insurance if this plant is on a property. In this country, I see that “Japanese knotweed is a dealbreaker for many Canadian mortgage lenders. Because of its destructive root system, banks frequently reject mortgages or require a multi-year, professional plan backed by an insurance guarantee to mitigate the risk.” We can only hope such a plan uses current and correct information.
So this year, we have some new thoughts and new information…please read to the end. But first, the main thing we want to say, to repeat, is that: Japanese knotweed is NOT LIKE OTHER PLANTS. Fighting this plant with logical, traditional, tried-and-true weed-eradication methods simply does not work.
Try and fail
On a walk around the cove in Freeport with my dog a few weeks ago, I met a guy toiling away, cutting down a patch of Japanese knotweed. Not with clippers or loppers (that would take hours and hours!). Not with a whippersnapper (some of the stout “bamboo” stems are too thick). With a scythe! It made me think of a Winslow Homer painting of a fellow systematically taking down wheat with even strokes of a scythe—hard work but marvelous to watch.
I watched him work for a spell, but didn’t want to startle him or talk his ear off! We did say hello and share a few words. He told me it was the third or fourth time this season he’s cut it back. And…it keeps growing back. This technique is perfectly logical and would work with a lot of other unwanted plants. Cut down repeatedly, a plant should falter, its root system should starve and die back.
Unless it’s Japanese knotweed. Cutting it actually seems to provoke this plant, causing it to quickly and often thickly resprout. As the famous saying goes, the definition of insanity is doing the same thing over and over, expecting a new/different result.
Mowing is madness?
I have seen plenty of people who deal with the Japanese knotweed on their property by mowing it. Little tiny reddish leaves reappear in their lawn within a few days or a week, and they mow again. And again. It’s a lot of work and if you take a week or two off, they grow taller and the whole project can get away on you.
Of course, if you somehow like having a stand of Japanese knotweed—this is an option. The thick growth can play the role of a dense hedge or “living fence,” blocking a view of a neighbor’s property or enclosing your yard.
But, I repeat, you are never going to get rid of it this way.
Tarping woes
Tarping doesn’t work either. I know. I tried it for several years with my patch. The stems just pushed up and through. Where I overlapped two tarps, they weaseled through and came up anyway—such ingenuity, such persistence. Annoying and, to be honest, a little scary.
I tried heavier tarps, weighted down with rocks. Where the sprouts and stems couldn’t break through, guess what? The plant just went out beyond where I tarped. This is because an established stand of Japanese knotweed is sure to have a huge, spreading underground root system. Tarping is like playing “whack-a-mole”!
I’ve even seen these plants cross a driveway or street—the smart money’s on the massive root system—likely it’s actually all the same huge plant, all the same root system. We are dealing with a beast here, folks.
Other things that don’t work
Digging up the roots. The problem with this method is that Japanese knotweed roots can grow wide and deep, and it’s very hard to get it all. And if you miss even tiny fragments, trust me, in time they will definitely regenerate. Established patches have been shown to extend 60 feet or. more AND go 10 to 20 feet down—are you prepared for backbreaking labor that might not, in the end, work?
Cutting off the flowers so the plants don’t go to seed. Well, that’s a management tactic for some other plants, but it won’t work with Japanese knotweed—don’t even bother. Here in this climate, viable seeds may not even have a chance to develop before winter comes. No, Japanese knotweed is not spreading by seeds around here. It’s spreading via bits of roots.
Burning. Setting aside concerns about the dangers of burning brush (especially now that our summers are getting drier, it seems), this is a bad idea. Japanese knotweed is native to Japan, where it grows on the sides of volcanoes. It laughs at burning. Don’t even bother.
Spraying heavily. You may feel so homicidal towards this plant that you attack it too vigorously. Various chemical sprays can scorch, damage or kill the leaves, bamboolike stems, branches, and flowers, yes. But the root system lives on, and it will resprout. More is not better, plus you can harm adjacent plants and your soil, or yourself, your family, animals. Do not go crazy blasting this plant with random garden chemicals or even “safe” formulations like vinegar. It won’t work.
Spraying at the wrong time. You might think springtime, as growth begins, makes sense—get ‘em while they’re young. But all the plant’s energy is surging upward then, and the toxin will not travel down into the root system, where it needs to go. Do not spray Japanese knotweed in spring or summer, tempting though it may be, as nice as it may be to see the dead, browned topgrowth…this condition is only temporary and the roots will live to create whole new stands.
One thing that has proven to work: spraying in late summer or early fall with weak glyphosate.
Let me just say that I only came around to this method after getting discouraged and failing at other methods. I’m an organic gardener and a nature-lover and it was hard to turn to a reviled weedkiller. Using glyphosate, I’ve come to believe, is like treating cancer with chemotherapy—a necessary poison for a greater good, saving a yard, habitat, or ecosystem.
Okay, here’s what to do. Spray “in the window” of opportunity between flowering and the first frost. Flowering, as with many plants, sucks a lot of energy, so the plants are overall weaker or vulnerable then. Spraying after the flowers fade spares the lives of pollinators, including bees, who—not knowing any better—seek sustenance/nectar from Japanese knotweed flowers. Also late-season Japanese knotweed plants (as with many other plants) are directing their energy downward now. (Spraying in spring always fails because the plant’s energy is surging UPWARD.)
Spraying at least two weeks before the first frost hits gives the spray enough time to work. Here on the Neck and Islands, I’d recommend taking action in late August through early September.
Mist the leaves (top and bottom of the leaves, if you can safely reach both sides); don’t let the spray drip, don’t drench, no need. Within the first hour or two of spraying, the leaves drink in that poison and convey it down into the roots below…where the chemical gets busy killing the roots. Even deep and extensive ones that you will never see and no shovel will ever reach.
This works. Typically a good August or September spraying session kills 90% or more of a patch of Japanese knotweed—it’s simply amazing. Give it about two weeks to show results (and enjoy viewing the extensive dead patch the following spring). Quick results mean you only killed the parts you can see aboveground; your real target is the root system.
You’ll have to follow up in the next year and beyond to kill stragglers and weird chemically distorted growth, again, in that window. Let the few survivors grow all spring and summer so there’s maximum foliage for the spray to land upon.
Some tips for success and safety:
Buy a product that lists ONLY “glyphosate isopropylamine salt” as its active ingredient. RoundUp has other products and formulations, so you need to check the label. If you buy concentrate, dilute it with water to between 1.4 to 4%, that’s it, no more; for me, the sweet spot is about 2%. (After, store the sealed container up high in a dark, cool place where nobody can mess with it, including kids.)
The generic recommendation is 2-4%. But most of us have been using the yellow jug of RoundUp that only has 1.4% —it’s pre-mixed—and have been successful. Look for “Poison Ivy Strength,” available at Canadian Tire and Home Hardware.
Spray in batches so you don’t have leftover. Glyphosate binds to impurities in water and becomes inert, so leftover will neither be toxic nor useful.
Spray on a windless day to avoid drift. If you have nice garden plants, bushes, or trees close by, drape them with old towels or blankets or cover with cardboard boxes so no spray can get on them. You only want to kill the knotweed.
Suit up in old clothes, closed shoes, gloves, even a Covid-era mask, and then launder the clothing and take a hot, soapy shower after. This is just being prudent. If you work carefully, you should not get any on you.
Never spray over your head. Some people cut their tall patch down in June, and spray the shorter regrowth “in the window.” I’m against cutting for any reason, honestly. Just spray what you can reach. It’ll work.
The following spring, if you want to clean up all the dead stuff, cut it and bag it and send it away in the trash. Never the green bin—heaven forbid you do anything to spread this problem plant! (And do not yank or tug at dead stalks; if there’s any life left in the roots, a possibility, you may provoke it into resprouting.)
Parting words:
Do nothing? Attacking Japanese knotweed incorrectly seems to provoke it. It will resprout or spread out with vigor. I have noticed some people who have it on their land and don’t do anything have somewhat less of a problem. Often a patch will only expand slowly if you leave it alone. Of course, I don’t really recommend this……in the end, you’ll be sorry because, over time, Japanese knotweed will spread out.
But what I’m saying is, if you’re not up for attacking it correctly at this time, don’t poke the hornet’s nest. Leave it be and take proper action when you’re ready.
I would also add that it’s especially distressing to see Japanese knotweed on an island…a contained ecosystem. Surely we can fight back and reclaim our natural habitats.
More information and moral support:
Look over or join these Facebook groups. You will learn a lot.
Japanese knotweed—Canadian support group
Worldwide Japanese Knotweed Support group
The one Chris mentioned that often has incorrect information and comments, but may still offer useful or interesting conversations, is: Nontoxic Japanese Knotweed Solutions.