British Columbia: can I drown out Japanese knotweed?

Discussion in 'Outdoor Gardening in the Pacific Northwest' started by kkuefler, Apr 18, 2015.

  1. kkuefler

    kkuefler New Member

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    I have a slope at the back of my yard that is filled with Japanese knotweed. it goes into the neighbor's yard as well. I have lived with it for five years, but I suddenly have an opportunity. The neighborhood boys have been playing jungle back there, and have cleared almost all of it! Yay! Is there something nicer and/or native I can get planted there quickly that might prevent or at least compete with the knotweed? It's not all gone, but at least 80% of it is. Seeding something wold be easiest, given the slope. I am not a 7 year boy who is unafraid to fall:-)

    Any advice would be greatly appreciated, thanks!
     
  2. Georgia Strait

    Georgia Strait Generous Contributor

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    i am curious about this as I see this same invasive plant around our area too.

    my understanding is that this plant has deep rhizome roots - so if all the boys have done is cut down the top visible part of the plant - then it will likely re-sprout, correct? (I need an expert opinion here)

    here is some info to explain what I mean - http://www.shim.bc.ca/invasivespecies/_private/index.htm
     
  3. kkuefler

    kkuefler New Member

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    Yes, I have read that as well. We have tried cutting it back before and it always regrows stronger. Because it's in my neighbor's yard ( actually she admitted she planted it years ago, but regrets it now), I doubt I can eradicate it. I'm just wondering if now that it is cleared I can plant something else that will slowly take its place, or at least reduce how much grows back. I have some laurels that have held their own beside it, but if I fill in with that, it will eventually get too tall and be difficult to trim.......
     
  4. Georgia Strait

    Georgia Strait Generous Contributor

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    gosh - if you can team up with neighbor, that might be your best approach.

    What square foot area are you dealing with on your side of the fence? And neighbor side?
    How steep is the slope?

    i can imagine how your neighbor feels - stupidly I actually helped to spread some alstromeria in my own garden - dumbest idea ever. (the pretty orange flower but VERY invasive plant - the seeds literally explode and spread so even planting in a pot isn't the answer)
     
  5. Georgia Strait

    Georgia Strait Generous Contributor

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    QUESTION - is the knotweed grove legally on your property or do you just kind of adopt slope adjacent to your lot line? (is it an undeveloped public road or something like that?)

    if it is on regional district / city /town property, then they should likely be addressing the situation - it is a well-known invasive and most local governments have plans for dealing with these issues.

    http://www.portmoody.ca/index.aspx?page=185
     
  6. Georgia Strait

    Georgia Strait Generous Contributor

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  7. LemonTart

    LemonTart Member

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    I'd be surprised if there's anything that can out compete knotweed, but I'm no expert so hopefully someone will tell us otherwise!!

    I've been beating back a clump in my yard for the last couple of years - this will be the third summer, which is how long we have lived here. The previous owner had been doing battle with it as well, though I'm not sure for how long. After reading up on it, the approach I've taken is to let it grow until early summer, expending much of it's stored energy (in theory, so far it doesn't seem bothered), then cut the stalks and drip undiluted RoundUp down the hollow stems with a syringe. Those stems die, and it shortly pushes out new shoots. Let it grow for several weeks, do the roundup treatment again. Continue until it goes dormant for the winter. I have read that this treatment, or a similar regimen of repeated mowing every few weeks, will kill it after ~4 years. Mowing is not possible in my location, which is why I'm resorting to the RoundUp (do not generally use poisons of any kind in my garden, but the knotweed is a special case).

    Really hope someone will chime in with a better solution than mine, which is obviously not feasible for a large patch. Maybe you could rake up the soil and take a tiger torch to it?

    If you attempt to dig it or pull it, be aware that you should not put this in your compost, nor the city compost if you have that in your area. It should be bagged & put in the garbage, or burned. It can regrow from a very small piece of root, so digging alone is often not successful.

    After the apocalypse, there will be cockroaches...and knotweed.
     
  8. kkuefler

    kkuefler New Member

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    Yes, nothing seems to faze it:-) my best hope is to try to at least tame it somehow. I can't do the roundup for several reasons. We have small children and a dog, and also neighbour kids who play in there. Also it's right beside a creek that runs through my yard and down to Rocky point. It's an area about 15 feet by 50 feet, so taking a syringe to each cane would be quite a production, and I know my neighbour won't do the same, so it's hardly worth it. The city has told us it's on our property and is our problem. All they do is trim the roadside edge of it periodically. *sigh. Maybe I should just learn to love knotweed.
     
  9. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    "Control" of [SEARCH]knotweed[/SEARCH] comes up frequently on the forums. As far as I know, not much has changed in the way of advice from what was posted on previous threads (have a read through the threads linked).
     
  10. Georgia Strait

    Georgia Strait Generous Contributor

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    DANIEL at UBC - how deep are the knotweed rhizomes, generally?

    i suppose it depends if it's behind a retaining wall etc - like "morning glory"

    but in general, can you say?

    thx.
     
  11. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Sorry, no real world experience with these. Resources online suggest up to 3 meters deep.
     
  12. Georgia Strait

    Georgia Strait Generous Contributor

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    ouch. Those are deep roots.

    does it spread in our part of the world readily by seed? (like "scotch broom" at the coast - or "hounds tongue" in Okanagan)

    or mainly rhizome?

    maybe a biological control is being worked on somewhere (didn't they make one for knapweed in Okanagan?)
     
  13. Georgia Strait

    Georgia Strait Generous Contributor

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    re: reproduction Japanese Knotweed - I just answered my own question - above -

    apparently reproduces mainly by rhizome and also garden waste dumping etc - it's the roots that need to be properly disposed and destroyed.

    lots of information about Knotweed and many more noxious (and nuisance) plants in BC

    http://www.agf.gov.bc.ca/cropprot/jknotweed.htm
     
  14. Sundrop

    Sundrop Well-Known Member

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    If you can't beat it, eat it.

    "The best edible part of this plant are the young shoots, preferably when they are about 15-20 centimetres tall (6-8). Depending on your taste buds you may think they have a lemony taste, some say it is more like rhubarb. Young shoots can be consumed raw or cooked and the growing tips and the unfurled leaves on the stalk and branches are edible. Stems can be sliced and steamed, simmered in soups, used in sauces, jams and fruit compotes. Japanese Knotweed is a great source of vitamins A and C. It also provides many vital minerals including iodine and is loaded with resveratrol." http://www.ediblewildfood.com/japanese-knotweed.aspx
     
  15. Ron B

    Ron B Paragon of Plants 10 Years

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    One of the worst infestations of Bohemian knot-weed (frequently misidentified as Japanese knotweed) I have seen was on a river terrace, that probably gets overrun by water sometimes. Many other infestations here are in low places, where the moisture and nutrient levels probably suit a vigorously spreading plant that annually produces large leaves on tall stems. Places that may also be subject to flooding or puddling part of the time.
     

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