Experiments at Home: Knotweed Control

We have a knotweed issue at home. For those of you who don't know, Japanese knotweed (Latin names have included Reynoutria japonica, Fallopia japonica and Polygonum cuspidatum) is an herbaceous perennial that was introduced to North America as an ornamental and erosion-control plant but turned out to be highly disruptive to local ecosystems, crowding out native plants, damaging roads and foundations, and spreading via root runners that makes eradication difficult or impossible. It can regrow from extremely small pieces, so it can't be composted or moved; it needs to stay onsite or be bagged and put into the trash can. More information is available from New York State at this link. Anyways, we have some, and I wasn't willing to jump straight to glyphosate. I also wasn't willing to let it go.

The first season I mostly hacked it back by hand, over and over, read up on it, and watched. I took an Old Ways Herbal online class to learn how it can be used to treat Lyme disease. I explored cooking with it using recipes available online.

This season, I have a few more strategies planned to help keep the knotweed under control without herbicide, fossil-fuel-based tools, or bags of trash:

1) Using a European scythe to cut it back routinely. This hopefully prevents the roots from storing energy and expanding, because the plant needs to put its energy into regrowing green material. A scythe is less exhausting than cutting it back by hand, doesn't use any fossil fuels, and doesn't fling bits everywhere to root and regrow the way an electric mower or string trimmer would.

2) Seeing if juglone makes a difference. My neighbors had a walnut tree that needed to be cut down, and I'm chopping the brush from it up into little bits on top of the cut-down knotweed. I'm hoping the allelopathic compounds in black walnut will help suppress it.

3) As soon as possible, I plan to put biodegradable paper mulch on top of the walnut brush, on top of the knotweed. I'll certainly do this before winter.

This is where plans get more tentative.

4) On top of the paper mulch, I might put a layer of wood chips. I also might just leave the paper mulch, and apply another layer of paper mulch in the spring after mud season.

5) On top of this new layer of paper mulch, next spring, I plan to utilize some type of livestock. This might be laying hens (who already live in our backyard), broilers (if that wouldn't traumatize our daughter), or miniature goats (if my neighbors succeed in talking me into it.)

(Oh! Edited to add one more thing: I've also been scattering the seed of aggressive native plants--including but not limited to wild geranium, ragweed, goldenrod, and Joe pye weed where the knotweed meets the grass. This is in the hopes that some of them can to some degree compete and form a bit of a buffer. I'm scattering the seed instead of planting plants because the disturbed ground would only help the knotweed more.)

I hope the mechanical barrier, combined with persistent cutting, combined with herbivory pressure, combined with some degree of allelopathic chemicals, will keep the knotweed in check. Will it? There's only one way to find out, so stay tuned.

Either way, this is an example of what I believe the future of the green industry calls for: experimental thinking; iterative and responsive ecological planning; a combination of active management and slowing down and watching; openly sharing our experiments, our successes, and our failures; and being open to some level of both physical and figurative "mess" as we work with our environment to figure it all out in a way that works for the whole ecosystem, ourselves included.

For more on just naming and a fairly comprehensive critique of the "invasive species" concept, please see this episode of the treehugger podcast: https://www.treehuggerpod.com/episodes/invasive-resistance