What would Japanese Knotweed do?

I know I have a minor and poorly minded blog, but I think I’ve found a unique way to manage Japanese Knotweed in New England (at least) and I want to share it.

Here’s the short of it:

  • There are labor or chemical intense ways to kill Japanese Knotweed. If you can’t do any of those, don’t kill it. Instead, make it play nice by turning into a spring ephemeral.
  • How? — Like this: when JK is growing, you can cut the shoots and eat them. You can cut the stalks and peel them and make “knotweed lemonade” or whathaveyou. But whatever you do, it’ll grow back…
  • But, when the stalks reach their full height, you’ll notice an obvious difference in the texture of the stalks when you bend them–before they’d break easily, now they kink but don’t snap… Once they become fibrous like this, you can cut them down and they won’t grow back to full size that year.
  • The Japanese Knotweed will continue to be there, and will grow back as a kind of creeper vine with much less height.
  • This docile form of knotweed will allow other plants to grow in and around the area. Some of these plants, no longer deprived of sunlight, may even crowd out the knotweed.
  • The point is: cut it down every mid-spring once it gets to full height, open the canopy and give the friendly JK a hug.
  • And finally, notice if it seems to spread or create any other problems and let me know so I can advance my research on this “living with knotweed” technique.

More detail:

There is plenty on the internet about how to try (and fail) getting rid of our invasive friend, JK. (Here’s a decent home-scale overview) And then of course there are those who say we should embrace Japanese Knotweed because of its medicinal properties and because bees like it, etc.

I’m a lazy pragmatist. But after seeing JK colonize whole banks of miles long creek and take over street corners all over western Massachusetts, I’m not so into loving it. To embrace JK seems to me to be a way to embrace a horrific monoculture of a future. Like all over monocultures, they’re our own handiwork, not nature’s. To wit, despite JK’s medicinal properties, frankly, this is no more or less medicinal than any useful plant–including a lot of the native plants that are literally shaded out under JK’s canopy and become endangered. I’d rather keep the diverse medicine cabinet than the single astringent Japanese resveratrol medicine. Some people have this notion that invasive plants are Nature’s way of healing itself from environmental compromise, like a fever is a way to heal from the flu. Anyone who knows anything about imbalances in a system and healing knows that reactions to instability are rarely helpful: though there’s some use to a fever, it can go way too far and actually cause a lot of harm–and that doing nothing in the face of a systemic disturbance (“embracing the new (invasive) wild!”) is at best an abdication of our responsibility to deal with the environmental problems we as a species have created. And at worst,  it’s throwing up our hands and letting Nature bake with a 105 degree fever. When we’re the infection. Probably neither nature nor we will survive if we did that whole hog.

That said, killing JK (and many invasives) is a losing battle. A lot is written on the Internet about killing it with Roundup. About digging it out. About covering it for 5-10 years with impermeable plastic. Chemical warfare doesn’t seem like a good idea unless JK is threatening to swallow your house. As for digging and burying, if you can do it–great. But the reports I’ve read seem to be pretty universal–if you’re going to kill JK for good, it’s gonna be a long hard battle–a lot of digging, a lot of cutting, a lot of time under plastic… I’m not one for long hard battles. So how about we do this a different way?

Well, I observed JK for a while. In fact, I tried to cut it down regularly and dig it out  following a protocol I read about a while ago for a sensitive wildlife area where herbicide couldn’t be used.

It just kept coming back.

But I noticed something interesting. If I cut it before a certain point, it would grow back. But if I let it get to full height, then cut it, it wouldn’t exactly die, but it wouldn’t grow tall again–it would just creep on the ground and be much smaller instead. So what’s this about?

Japanese Knotweed is a relative to Buckwheat. This is striking because buckwheat will do something similar: if you mow it before it flowers, it’ll keep growing. But once it flowers, if you mow it, it dies. This is part of how buckwheat is managed for soil biomass… It produces stalks and rich green leaves, and finally flowers–and then you mow, and because it hasn’t gone to seed, it simply goes away for good. Knotweed is similar, but doesn’t die, of course. And unlike buckwheat, which has been bred to start its flowering process more or less as soon it gets to its full height, knotweed doesn’t flower until late summer here in New England. But it seems that both JK and buckwheat use a lot of energy to get to that lignified stage when they’re full grown and fibrous. At that point, like noted above, knotweed is stiff and has a different kind of stalk strength than it did when smaller. Of course, JK is used to a million pests and to volcanic eruptions. Nothing kills it. Didn’t we already establish that? It’s worth noting that grazers (goats!) usually only like knotweed before it gets fibrous. So this full-height-cutting is an extra insult. The point is that, at least for a season, it’s stunted.

Why is this interesting? Well–here in New England, JK start growing in April and reaches full height by early June. This is a little later than the norm, but follows the essential pattern of spring ephemerals. Spring ephemerals are plants like ramps, trout lilies, blood root and trilliums that only are active for that brief couple months when it’s warmish but the tree canopy isn’t fully grown in, when there is sunlight on the dense forest floor. After the ephemerals go dormant, the ferns and bushes grow in, and the maples and ashes and birches are full of leaves. Japanese knotweed is so invasive partly because it’s an early riser and it crowds all these normal season plants out, coming out more or less when the ephemerals come out (but then it doesn’t go away). So what if, rather than killing JK, we simply get it to play nice by making it a spring ephemeral?

This is sort of like putting the gremlin in a suit and bow-tie, and putting a teacup in his hand and taking him to a tea party. I know. But stick with me.

Though there are certainly cases where this won’t work so well (ie, on barren salty roadsides), and there’s an argument that you should never let knotweed get to full height (to prevent successful photosynthesis), what I’ve observed is that this full-height-cutting allows in knotweed’s neighbors, including (hopefully) native plants–but at least less problematic non-natives–to come out and play. In the part of our property where knotweed is flourishing, I wasn’t even aware of the other plantlife in the area until I did this. Though the knotweed came back in a stunted form, it was even hard to find among the brambles, the burdocks, grasses, and other plants. It is quite possible that this other plant life could out-crowd the gremlin once JK is deprived of its height and sun advantage. I would wager that rhizomous, warm season grasses (as they used in this study) could do this well. You could even plant some fancy grass or aggressive native groundcover to accomplish this very purpose. Of course, you must remember that the point isn’t necessarily to kill JK–just to tame it. This taming strategy work well even in a forest if you don’t mind scything JK once a year.

Potential problems?

Well, a couple:

Though I’ve observed this stunting phenomenon a few times now, I have seen JK manage to regrow more strongly in a third area–almost to full height but not quite. This was along a salty dry roadside where nothing (and I mean nothing) could grow except knotweed. My hunch is that that knotweed was extra strong and had the energy to do bounce back in that case.

Also, this may only work in New England…? I don’t see why it wouldn’t work elsewhere, but yYou’ll have to try it and let me know.

And finally, paranoid logic would suggest that if you cut knotweed like this, you could encourage it to spread vegetatively. In other words, if you have a 5’x5′ stand of JK this year and you cut it as soon it gets to full height, maybe next year you’ll have a 6’x6′ stand or worse. I haven’t seen this, but I suppose it’s possible. It’s also possible that, no matter what you do, you’ll have a 6’x6′ stand–that knotweed, being what it is, grows outward without restraint. This amounts to a damned-if-you-do logic that paralyzes any action except bombing the whole neighborhood. What I’d suggest remembering is this: if you have a weedwacker or a European scythe, cutting a 6’x6′ stand or even a 8’x8′ stand of knotweed isn’t much harder than cutting a 5’x5′ stand. And however large the stand, if you’re doing this right, JK is still playing nice after you cut it, so its spread isn’t going to matter as much.

Thoughts? Observations? Let me know if you try this and what happens.

PS: Don’t dispose of knotweed root or plant matter in another area besides where you cut it. This probably goes without saying if you’ve been around the block a time or two. The only exception to this rule is in a biogas generator. Yeah? Right? You with me? Japanese Knotweed: the infinite source of low-lignin biomass. Along with garlic mustard. And artemisia. And black swallow wort. and Asian wisteria and bittersweet. A lot of biomass out there. Anyhow, a project for next summer.

Also, you’ll probably figure this out. But, when you eat JK… Well, let’s just say, don’t eat too much unless you’re feeling stopped up. It’ll got a knack for keeping people regular.


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