What is the best plan to contain Japanese Knotweed?


I recently purchased a property that has a rather impressive expanse of Japanese Knotweed. I have more-or-less abandoned the idea of eradication. From the research I have done, it appears like a lost cause. Are there any tips the office can provide with containment? Specifically to Maine (does the short growing season and deep frost line provide any benefit)? I’d like to keep it’s footprint as small as possible.


Jonathan Foster, Special Projects Assistant

I’m very sorry to hear about the Japanese knotweed infestation–you can take some small solace in the knowledge that you aren’t alone in dealing with this headache.

First, let me provide a couple of resources for you:

State of ME Natural Areas Program fact page on Japanese knotweed (quick read)

State of NH Dept of Agriculture booklet on Japanese knotweed (far more in-depth)

The short version is that once established, it’s very difficult to control and will out-compete just about everything in its niche. While I like the way you’re thinking about plant issues in general, unfortunately, our short growing season and long winter don’t do much to depress the species’ growth. Frequent mowing or burning, along with the careful application of glyphosate (as always, reading instructions carefully and following them conscientiously) are the primary methods of intervention, and for a large stand, it’s a long term project. You can stay on top of it, and I know people anecdotally who have persevered and triumphed, but it will require diligence and effort.

I’m very sorry not to have more positive news/advice for you, but I wish you good luck and happy gardening, nonetheless.