Japanese Knotweed-how do I get rid of it

catie(z3-4 PEI Can)November 11, 2005

I have a terrible problem with this INVASIVE weed. In attemptng to kill it, you stimulate it and it sends up many more shoots to take over. The shoots are extremely tough as well as the roots. We are now going to try to cover the area this fall with carpeting to impede the sunlight and 'hopefully' with the amount of snow we receive in winter, in the spring there will be less to deal with... I hope!

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jancarkner(Ottawa CAN)

It will find its way past the carpet no matter what. You'll probably need RoundUp (repeated doses for several years).

    Bookmark   November 16, 2005 at 3:15PM
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The heavy guage plastic is a good idea and the plant...often referred as Canadian Bamboo...is indeed one of the worst invasives. All you can do is dig...dig and more digging. Then use Round-Up. As the shoots may come from the roots, all you can do is keep cutting them off.
Sooner or later the roots run out of energy....sooner or later.

This is an exceptional plant for ensuring a slope doesn't erode, great for hillsides near water.

The problem with this, if you have a clear ground that you want something growing, then Knotweed is the answer...but if you have any nearby plants...especially honeysuckle, it will take over.

Anybody have an aspirin?

    Bookmark   November 20, 2005 at 11:59AM
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franeli(z4 NH)

Hate this plant.
We've tried digging roots out, helps, but you have got to keep at it!
My mom used a weed killer, I think 24-D on hers(not my idea+I would never do it) and it still 'popped' up after several years!
Digging and smothering has kept ours a bit under control.
I think if I had planted some native shrubs last spring, maybe it would help? Had some awesome spring ephemerals(this past spring) come up where that 'stuff' used to be!
We might try 'injecting' round-up low down near the root system next year.
NH Audubon is experimenting with something this spring on several of their properties...I'm keeping a close eye+ear out...

    Bookmark   November 23, 2005 at 10:22AM
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MikeL_Pa(5b/6a NW Pa)

We have more or less eradicated the 5' square patch we inherited from the previous owner 6yrs ago. Ours was right under a 60' tall 100 year old spruce, so digging was not an option. My advice, and what worked here - Let it grow until August until nice fat canes develop, cut them off 8" above ground, jam a stick or icepick or something 8" -10" long down the cane to break the membranes inside, and use a big syringe to fill the cane with concentrated roundup. For the next few years you should get at most small twisted and stunted 6" clumps where you had 7' tall jungle before. It is now very easy to pull anything that comes up.

    Bookmark   December 20, 2005 at 12:10AM
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I've been actively battling it for going on four seasons. It has spread into four neighbouring yards. I have a pie shaped lot. I also have a swath in my yard that is/was 24 inches by about 40 feet. I tried chopping and digging, breaking a few shovels in the process as well as using a rented mini excavator. That seemed to invigorate the roots and they spread out to about six feet wide. I tried various not so poisonous products, granular pool chlorine after wetting the leaves, vinegar and table salt as well as boiling water. two seasons ago, I tried pulling and applying ready mix roundup. Last season, I leveled the clumps and ran over them with the mower and then sprayed the 'stumps' with FULL STRENGTH Roundup concentrate. About every three to four weeks, I re-apply the round up.I've got it about 90 percent controlled in my yard. I plan to continue this in the upcoming season and hopefully eradicate in my yard and tackle my neighbours yards as well. It was growing when I bought the place 9 years ago and like the instant privacy fence, but started to resent the bees, hornets and wasps in late summer. It seemed to hold the mosquitoes during the day as well. When I mowed the lawn, I would be attacked when I brushed aganst it. It was also a pain to remove all the dead stalks in the fall.

    Bookmark   January 12, 2006 at 8:36PM
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nyssaman(Z6 ON)

A flame thrower comes to mind...lol


    Bookmark   January 21, 2006 at 3:06PM
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triple_b(BC 5b)

Hand grenade? Oh never mind. It would spread root bits far and wide to regrow, and that's what it WANTS us to do, isn't it? I can hear it pleading now, just like Brier Rabbit: 'Oh please, DON'T use the hand grenade!'

    Bookmark   January 26, 2006 at 12:05PM
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DianeKaryl said: "This is an exceptional plant for ensuring a slope doesn't erode, great for hillsides near water."

It really isn't. It's a terrible invasive pest and a small fragment of root can travel far and spread it. This occurs particularly along waterways and is a plague in many natural areas along rivers and streams. There are doubtless natives that could fulfill the same function and would not cause the same problems.

    Bookmark   May 23, 2006 at 10:15AM
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pam_whitbyon(6 Niagara)

Actually, Jeff, you're right on the money with the flame thrower! Fire is one of the few ways to get rid of this nightmare, but it's not too practical for most.

This plant is a big concern. It's destroying all of SW England and is a bigger problem in the maritime provinces of Canada than in the rest of the country.

My sister thinks she has finally got rid of hers. Ironically her house was previously owned by a horticulturist who planted it over 30 years ago when it was in vogue. The problem is, though, it's reached over into her neighbours yard and they are not going to do anything about it - language, cultural differences and complacency have been the obstructions, so it's all a matter of time before it comes back onto her property!

Somewhere on the internet there's an amazing picture of this plant actually growing up through someone's inside wooden window sill! I was looking for it today again but can't find it.

Good luck!

Here is a link that might be useful: Fact Sheet on Japanese Knotweed

    Bookmark   June 5, 2006 at 12:20PM
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I noticed you're a NH resident. You don't happen to live near Twin Mountain, do you? If so, you (or your spouse) may be the person I spoke with a few years ago about eradicating Japanese knotweed. As I was driving by your house, I saw you out in the yard, cutting Japanese knotweed stalks, and decided to stop to talk. I've often wondered how your eradication project has progressed.

Here is a link that might be useful: Japanese Knotweed

    Bookmark   July 11, 2006 at 2:13PM
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sassie60(Z4 ON)

Wow, I'm sorry to hear you have such a problem with this weed. Check on the google search engine and you will find some interesting readup on this noxious weed. I'm having my problems as well with what's call "field horsetail" that's growing in my flower gardens so I can appreciate what you are going through.

    Bookmark   July 23, 2006 at 9:20PM
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My husband and I have been fighting this menace since the summer of 2005 - it came with the house.
Year 1 in summer cut down canes and fill with RoundUp. Just before Fall dig out root clumps and spray RoundUp on anything that was still living. We thought that would be the end of it.
Year 2 in Spring dig up remaining large root clumps (can't get to the one growing in the old stacked stone wall...yet). During the rest of the summer weekly harvesting of new sprouts from slope and back lawn - weed spike works nicely. Dispose of in sealed plastic garbage bag.

Year 3 - the snow has melted and we've started our seasonal "Knotweed Patrol" in the yard.

The plant is a big problem here in the Hudson Valley region.

Vigilance and persistence.

    Bookmark   March 26, 2007 at 5:00PM
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We have a huge border of this plant around our property. While I like the screen it provides, I'm just tired of it making a mess every fall.

So we're attacking it with a vengeance this year, starting now. At the moment all I am doing is clearing the debris from the last two years, but as I uncover the roots I'm going to try injecting weed killer (RoundUp or Killex) straight into the exposed rhizomes. And through the summer injecting the growing plants as well.

One patch behind my shed I'm going to spray well and then cover with plastic and maybe gravel as well.

Also planting replacement plants in the areas as they're cleared.

It'll be an ongoing attack though I expect, as within a half mile there are acres of the stuff.

    Bookmark   April 10, 2007 at 9:10AM
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The way I found to remove knotweed is using your weed trimmer cut it down each week from spring until mid August(the plants will be small and weak by then). Then let it grow until it flowers, at this point you can shoot it with Roundup. This will kill 99% of it. The following spring after it gets a few inches tall spray any remaining plants with Roundup. That is what we did and four years later there has been no regrowth. Best of Luck.

    Bookmark   May 2, 2007 at 9:07AM
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jbann23(6 RI)

Chester525 - You got it!! I've had the same experience spraying at the end of the growth season. Killed the roots over the winter. Just have a small bit left to deal with. I'll keep it cut down and hit it again this fall and that should do it.

    Bookmark   May 11, 2007 at 10:19AM
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We inherited knotweed when we moved into our house almost two years ago. After discovering it wasn't bamboo (I'm so naive!) we began an all out onslaught on it.

I read into it a little bit and found a site that notes in Clark County, Washington, they did an injection of herbicide (something like Roundup concentrate) and it was 90+% effective, so here's what I did:

I got some needles and syringes and injected Roundup concentrate right below the lower nodes on the large canes. On small canes (less than a 1/2 inch in diameter) I cut and poured round up concentrate. I also cut and poured with some of the large canes too. With the really small stuff, I took some Lilly Miller Blackberry Killer and poured it into a plastic dish and painted it on the leaves.

The injection worked (so far anyway) about 95%. We didn't get any new shoots from the clumps where I injected the canes the previous year. There were some random shoots here and there, but smaller.

Your best attack is to inject or cut and pour and paint on killer. Whatever you do, don't pull them. Even an inch of root can start a new plant. I did pull out the big root trunks on some of them and haven't had any problems, but I noticed when I pulled a couple of those huge clumps out, there were some new buds starting.

It's really an amazing plant (don't get me wrong, every time I see it by the freeway or on a slope, I have fantasies of injecting it and watching it wither and die). It is great for slopes and erosion control. I also actually looked into harvesting it for medicinal uses, but it'd be hard to compete with the Chinese market.

But seriously, like people say, it is just something you have to deal with for several years. Just don't let it drive you crazy.

    Bookmark   November 25, 2007 at 2:29AM
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Hi everyone, for anyone suffering from this monster be thoughtful for those in jolly old Blighty. Over there they have suffred from this plant since Victorian days when it was planted to stabilize railway embankments. Now it is widespread, it can often be seen breaking through concrete roads.A friend of mine had acreage and it was full of the stuff and after trying many things his best ally was his weedeater. He would attack it weekly and after a few years his fields were largely clear. In Britain it is illegal to transport this weed so when you dug it up or cut it down you were stuck with it and your only option was to burn it. So to those with this weed please do not take it to the dump, it will grow again and someone else will have it. All the very best, Robbyroos.

    Bookmark   March 14, 2010 at 11:38PM
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My father actually likes this plant, and tried to fertalize it to make it grow better.... go figgure!
As a result, we have found its weakness. and I have menaged to sucessfuly remove it from the yard of my summer cottage, in under 2 years, with minimal work.


Clean up all the old growth in the spring,cutting off any emerging shoots as well, and LIBERALY coat the ground with lime in the affected area. Re-apply lime whenever you notice that it has all been washed away by the rain. Cut off any shoots as they emerge ( lawn mower works great!!) and dig up the root clumps as they die and loosen.

This stuff can live covered up under plastic for 5 years or more, and send roots down to a depth of 3ft! It also takes only a 1,inch piece of root to start the "infection" of a piece of property!

The best part about the lime treatment, is you get an realy healthy crop of grass whe you are finished, and you dont have to break any anti pesticide by-laws to get the job done!

    Bookmark   May 15, 2010 at 9:31PM
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Goats like the new shoots.

I had a small patch near the house. I dug and cut and chopped. I finally resorted to the cutting of canes and adding roundup in the hollow. Even then it took several applications.

It isn't an ugly plant but I've never seen anything take over like that does in the north!

    Bookmark   May 21, 2010 at 6:26AM
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Is using lime for eradicating knotweed harmful if my cats sleep in that area?

    Bookmark   May 28, 2010 at 9:32PM
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I have a problem with this mean weed. I have been simply clearing it, not knowing what else to do. The folks at the Montreal Botanical Garden say there is not much to do about it and the safest bet is to keep clearing it so it never really gets access to sunlight, which would eventually weaken it to the point of death.

I have been sick and tired of this weed, especially since it was taking up all the room I had to grow vegetables. I built two ten-inch deep raised beds out of wood planks. I stretched heavy (pro grade) landscaping fabric out under them, filled with yummy soil and planted veggies. One of my beds has a six-inch landscaping fabric overlap (bed A), but there was just barely enough fabric left for the other to have a one-inch overlap (bed B).

I am happy to report that there is absolutely no knotweed to be seen in and around bed A. As for bed B, sprouts came up along the landscaping fabric overlap. They grew right among my bush beans, but it isn't a problem, as the colour of the bindweed is easy to spot because it clashes with the bean leaves. I rip them out whenever I find any, and my beans are producing nicely.

So, the conclusion I have drawn from this experience is that if you cover the ground so that absolutely no light gets through and if you weight it all down considerably, the bindweed chokes. I think that folks who tried covering with plastic and weighing down with bricks and stones failed only because whatever weight you apply has to be uniform and heavy. If you only place rocks and bricks at intervals, you are leaving room for shoots to push through in spots where there isn't any weight. Trust me, this weed has a knack for finding the slightest hole to push through, so you have to use something granular and mercilessly cover every square millimeter of ground.

Next year, I am planning on covering the entire area with landcaping fabric, installing my new, improved raised beds on top of that and filling in the paths with concrete blocks (which will be laid on a few inches of sand). I will report again next year.

To those of you who are willing to invest a bit into choking bindweed, I suggest using landscaping fabric with a minimum six-inch overlap, covering that with about two inches of sand (to ensure that the layer on top of the fabric is fine and compacted), and then covering that with at least four inches of fine rubble (particles not exceeding an inch in diameter). However, I also noticed that whatever growth did manage to surface is trying to jump the fence to the neighbour's, so I recommend covering a larger area than the area affected. I think a four foot margin would do. So, if the affected area is a four-feet wide swath, you would be covering a width of twelve feet.

Has anybody else managed to control japanese knotweed by covering and weighing down?

    Bookmark   August 15, 2010 at 2:02PM
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I have Japanese Knotweed on the slope in front of my house in Southern Japan.

Knotweed (kudzu/kuzu, or kazura/kadzura) is a problem here in Japan too. The hills are covered in it although they say that it has a natural predator and some sort of insect is eating its leaves.

I am thinking of using Roundup on the roots about now (late August) but seeing as how I live in the land of knotweed, I am also thinking that I should live with it.

As noted above, it does prevent soil erosion on my slope. It does produce a lot of dead stalks in Autumn, but they are fairly easy to bundle up (epecially if there were only knotweed, no trees). The stalks are pretty easy to cut, never needing to saw.

It keeps the trees in check and the trees, that can grow tall, spoil the view and their harder branches are more difficult to deal with (I am bagging and binning plant waste).

My dogs eat knotweed.

So perhaps I should just learn to live with knotweed, and keep it out of my neighbours garden. Trees do not grow into neighbours gardens, but knotweed does. It is this anti-social aspect of knotweed that seems most problematic. Even if one does not mind it oneself, it is going to get into everyone elses property and upset those that hate its guts.

I am not sure what to do, but I am pretty sure that I am not going to win.

Here is a link that might be useful: Japanese Culture

    Bookmark   August 25, 2010 at 9:11PM
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I was able to eradicate a small (100 sq. m) established patch of knotweed by manual cultivation. I pulled those I could, and chopped the rest to the ground, three times each growing season (in May, June and August). This reduced it by about 75% each year, and eradicated it after the 4th year.
Advantage of manual method is that it avoided herbicide contamination of adjacent pond and wetlands, and allowed interspersed native shrubs to take over. Disadvantage is that it requires persistence and effort. Location: NW WA.

1 Like    Bookmark   April 11, 2011 at 7:56PM
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one thing to note is that the young sprouts can be eaten, though if you've been treating it with round up you might not want to. you can use it as a substitute to rhubarb. i used to feed it to my rabbit and he loved it

    Bookmark   May 11, 2011 at 8:56PM
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Did you know that herbalists use Japanese Knotweed to treat Lyme disease? The roots are dried and used as an oral supplement to kill the spirochete bacteria. I just thought it was ironic that lime is used to kill Japanese Knotweed. Don't kill all of it please.

    Bookmark   June 13, 2011 at 11:28PM
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Well, we're into year 4 of trying to get rid of this hideous plant. I started by pulling as much as possible and then digging up the root clumps,but they break and the plant returned. Roundup worked pretty well, but you have to be careful of other plants and trees. I have had them pop up 30 feet from the yard. They are becoming easier to pull and we found that sticky monkey flower (wildflower) actuall prevents the bamboo from growing in that area

    Bookmark   June 14, 2011 at 10:53AM
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Wherever we have had a long bonfire, the knotweed did not come up again (2 years and counting). Flame torch does not work. You need a long burning fire to achieve root burn. Good luck and be safe. Have shovel and water ready and dig a line around the fire area. Goes without saying you should not use this method by structures or other flammables.

    Bookmark   September 2, 2011 at 5:23PM
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I've moved house 3 times in the past 20 years, each time to a new country (Italy, Belgium and Sweden) and by some beastly coincidence, have discovered Japanese Knotweed waiting for me in each place. My current battle takes place at latitude 62´┐ŻN, which is close to the most extreme northerly extent of this hardy plant.
Tarps and light-tight membranes may work but (a) it can easily grow out past the edge, so all you do is spread the problem, and (b) apparently it can hibernate for as much as 20 years, so your membrane has to be there for a long time.
Digging is difficult, first because a well established plant can have a root system at least a metre down, and sometimes twice that, as I have personally discovered. Second, leaving even a little rootlet can mean you've just planted another one for you to do battle with a couple of years down the line. Getting the root out with all its rhyzomes is a major task and typically involves serious earth-moving equipment.
Roundup is effective, but you have to go slowly-slowly - they say that a rapid high-intensity assault causes the root system to close down and hibernate rather than die, so it may well pop up again a few years later.
Chopping and mowing can be really bad, bad solutions because the plant can grow from a fragment of one of the nodes where the leaves come out. If you chop or mow into a bag, and get rid of the contents of the bag by burning, fine, but if you just spatter the surroundings with bits of plant, you could be doing the plant a favour.
From my Italian experience in getting rid of the thing, you have to have patience, and attack it with a variety of means, and be ready to keep on dealing with it for several years. I finally got rid of the problem by moving house, but the infestation was slowly succumbing to a mixture of treatments - cutting it down (carefully) whenever it had started to look happy with life, meaning about 3 or 4 or 5 times a year, and then, in the autumn, letting it grow reasonably big and then spraying its leaves with glyphosate (Roundup). http://dnr.wi.gov/invasives/publications/pdfs/japanese_knotweed_control.pdf recommends painting the cut stems with concentrated glyphosate, but I haven't tried that.
My new infestation is located partly under my wooden house, which as many houses in Sweden, is raised on low pillars. This pretty much rules out digging - which is OK by me. But it also means I do have to get rid of it since I don't want to share my bedroom with a Japanese plant.
Winters are cold here, and we can get down to 30C degrees below freezing. I've been told that one (experimental) way of weakening the plant and making it susceptible to the other attacks is to hammer a metal pipe into the middle of the plant root system in the autumn. The idea is that when it gets really cold in winter, the the pipe carries the cold into the ground (normally the snow acts as a blanket), slowing the root down and weakening the plant over several years.
Currently the plant is sulking under a black membrane and some paving stones, but I'll try the pipe treatment a bit later.
The real battle will begin next spring.

    Bookmark   November 9, 2011 at 10:39AM
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The information you shared in the post related to the Japanese knotweed is very useful. I must say that one should always look forward to the control of such weed otherwise it can damage the building and other parts due to it's rapid growth.

Here is a link that might be useful: Japanese Knotweed Specialist

    Bookmark   July 13, 2012 at 4:57AM
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Hi All
I fully understand the upset and worry this plant causes everyone who has it in their garden or property. I myself have had the headache of getting rid of this from my garden. Thankfully I have found this company www.sghmaintenance.com who have already managed to tackle this problem for me and have relieved me of some of the worry. I've set a 2/3 year plan with them so I haven't got to pay a big amount in one go, this was one oft main worries.

    Bookmark   March 17, 2013 at 7:07PM
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the knotweed will grow under the carpet we did this when we purchased our home and had it everywhere. what we did is try and find the main root ball the biggest one, dig it up deep to get as many roots as possible, just pulling by hand will not do it, when you break it off the liquid inside the shoot regenerates to make it grow again you will have to do this for a very long time, it took us 4 years to clear our yard up and we still get shoots that pop up so we dig them up and keep the process going, hope this helps

    Bookmark   April 20, 2013 at 3:59PM
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Dilute at the rate of 1 part herbicide to 40 parts of water for treatment of most prenial weeds and 1 to 40 for treatment of hardy invasive plants like Japanese Knotweed and 1:20 for Ivy

Here is a link that might be useful: Knotweed Control

    Bookmark   June 17, 2014 at 10:08AM
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SouthCountryGuy Zone 4b-5 SE BC(Zone 4b-5 SE BC Canada)

Spammer suck.

    Bookmark   June 30, 2014 at 11:24AM
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