Meditations on Giant Knotweed - is there a middle path?
April 15, 2018 1:46 PM   Subscribe

One of the most dramatic and useful features in the garden of my new house is a stand of about 100 stalks of Giant Knotweed. When I Googled for advice about how to prepare the patch for the upcoming season, all of the results pointed to its awfulness, invasiveness, and how I am a terrible person for encouraging its growth. Is there a middle ground with Giant Knotweed?

It blocks the patio area from the road, was full of honeybees in the summer, and seems like someone worked very hard to cultivate and contain it to an area with a stone-wall edging. I don't see any other stands in my neighborhood, and like I said, it is well-contained for now. I am in MA and can't seem to find any state-wide or local regulations regarding knotweed. I absolutely love it and is essential for the privacy of sweet little backyard. I am a conscientious gardener, and I want to make it work without being the Jerk With The %@!$% Knotweed.
posted by bright and shiny to Science & Nature (20 answers total)
 
Also, if I must remove it, is there another tall and full (and fast-growing) plant that will achieve the same effect of blocking the view into my patio area and will feed the bees?
posted by bright and shiny at 1:56 PM on April 15


Pictures? There are several related plants in the knotweed family that may produce different advice. Also maybe a picture of its edging to get an idea of its containment? I’m not a knotweed hater either (in general) but like I am coming to realize with my rose bushes, sometimes things are lovelier in other people’s places than in our own.
posted by dness2 at 2:00 PM on April 15


While there could be containment by visible barrier, the rhizomes can go to a depth of 7 feet. The seeds are also a big problem. Your plants could be spreading this damaging plant all over without you being aware. Find your local Master Gardener program (often at college extension programs) and ask them about how to dispose of this plant and also what to plant in its place.
posted by quince at 2:12 PM on April 15 [2 favorites]




The other side of the stand

I get that it has to go, and there is no evidence, nor any over the summer, of its spread. I am wondering if there are any tips about management, as a middle ground, in between now and when I will have the resources and knowledge to replace it.
posted by bright and shiny at 2:16 PM on April 15


You could consider a stand of clumping bamboo. People freak out about bamboo but it doesn't spread via the wind and seed, it sends out shoots underground. However, clumping can spread but it is not as invasive or as hard to contain as running bamboo. You could also put it in one of those big metal troughs which raises the bamboo and provides its own visual barrier. Bamboo is evergreen. If you choose a bushy clumping bamboo, you would have year round prett stalks to look at. You will want to prune it so it has room to send up new shoots. You can cut old canes and use them in your garden as well, to make little fences, or trellises for other plants to climb.
posted by amanda at 2:32 PM on April 15 [3 favorites]


It produces a dark and quite interestingly flavored honey, as I recall, and bee keepers love it because it's peak (and copious) nectar flow occurs at a season of the year during which very little else is available.

I've often wondered whether some Asian plant might produce a nectar which would help European honey bees resist the Asian verroa mite -- because anything which would help a prolific pollinator would help the plant -- and the strong flavor of knotweed honey would make it a candidate, I'd think.
posted by jamjam at 2:35 PM on April 15 [1 favorite]


Very last comment, sorry. I am looking online and I believe that it is Bohemian Knotweed rather than Giant. It looks like the Bohemian version does not produce any seeds, but spreads via root fragments and rhizomes...
posted by bright and shiny at 2:43 PM on April 15


Japanese Knotweed is classified as an invasive and prohibited plant in Massachusetts. If you determine that it is Japanese Knotweed, the second link has answers to some of your other questions about growing it in your yard.

Jamjam's comment about bamboo honey is correct - as a beekeeper, it does produce tons on nectar flow, only for about a week in the early fall here in New England. It's also edible!

(I've been trying to kill a stand of Japanese Knotweed for over a decade. Once I think I have the area clear, it somehow comes back a year or two later.)
posted by bCat at 2:54 PM on April 15 [2 favorites]


That looks like Japanese knotweed to me, but I dunno it’s hard to tell in the winter. But either way, it is not at all well contained for a knotweed. They do most of their spreading underground, like quince says way underground, so that flimsy little wall won’t do anything. And it doesn’t look like you are surrounded by tightly maintained areas, so you probably also have shoots coming up over the road or in other areas around your house. Think of the roots of your stand as the ant queen. You can groom what you see above ground but that does nothing to control how busy she is below. You need to get rid of it yes, especially if you are anywhere near wet areas. It’s too bad you don’t have goats. The good news is it’s going to take a little time to get rid of it and there’s no way you can plant any replacement there for a little bit. I would actually put in a little fence or screen. Two 4x4s and some six foot boards spanning the space, and try to keep that dirt area plant free for a couple years until it’s safe. Pressure treated wood and deck screws would last for a few more years after than and be a nice backdrop to hanging strawberries or something. Just an idea.
posted by dness2 at 2:57 PM on April 15 [2 favorites]


Like maybe one panel of this: horizontal fence With a lot of mulch at the bottom. It might look classy!
posted by dness2 at 3:10 PM on April 15 [1 favorite]


Hi.
My qualifications: I garden for a living. I grew up in MA.
Kill it. Please. It is invasive in a horrible way.
There’s a joke about knotweed: what’s the best way to get rid of knotweed?
Answer: bulldozer.
posted by sciencegeek at 3:33 PM on April 15 [12 favorites]


I don't know all the various flavors of knotweed, but that does look a lot like the Japanese knotweed that's a scourge in my area (western PA). The only reason I'd consider not killing it is that it's a hopeless battle. Four years ago I tried to eliminate a single plant that a neighbor pointed out in my yard. I've cut it down and filled stems with Roundup numerous times, and dug up a huge area, sifting roots out of the soil. It still throws up new shoots every year.
posted by jon1270 at 3:53 PM on April 15 [2 favorites]


I've been trying to eradicate knotweed from my yard for 17 years now.

Every time I come close, it pops up again... in part because my neighbors let theirs grow. I have to mow in areas I'd prefer to have flowerbeds or wildlife habitat because it's the only way I can minimize it. Try not to be That Neighbor.
posted by metasarah at 4:35 PM on April 15 [2 favorites]


I can confirm that knotweed produces a delicious honey. If you’re in southwestern Pennsylvania, look for ‘bamboo’ honey from McCormack Apiaries. It’s available at at least one Giant Eagle, Agway, and farmers markets.
posted by ReginaHart at 4:45 PM on April 15


The persistent stems look a lot like Japanese knotweed, but either way, my understanding is that both giant knotweed and Bohemian (Japanese x giant hybrid) behave similarly. As others have said, for established plants it's the rhizomes that'll get ya. This plant is very difficult to kill, in my city it has spread and taken over acres and acres of riparian habitat, which may have been somewhat degraded previously, but is now a Japanese knotweed monoculture. If it is alive, it will spread... that's just the way of invasive species.

I completely empathize with wanting the privacy screen... I'm in the midwest so I don't have much to offer for alternative recommendations, but most states have a Native Plant Society group which you could hit up. Regarding the pollinators, it is true that these knotweeds are pretty attractive to insects! However, pollinator populations are nearly always better served by native species, which are more likely to cater to specialist insects with particular floral requirements, rather than just generalist and/or non-native species, like honeybees. (No offense to honeybees, but they still get the majority of the conservation PR, while the also-struggling native pollinators just don't get as much attention.)
posted by Ornate Rocksnail at 5:08 PM on April 15 [2 favorites]


Knotweed is edible. If you have livestock you can feed it to them. Bring in a cow or a horse or some sheep and your knotweed will be pruned for you. It's also a decent spring green for people and the new leaves are edible all year round, but the spring ones are best.

I find that waiting until it is about two feet tall and cutting it back does a lot to discourage it, because it spends lots of energy on that growth only to have to start over again. That seems to slow it down better than going after the brand new shoots. If I eradicate those it seems to spread out and try a little bit further over. I make sure to cut it before it flowers at the very latest.

I will never be free of knotweed. My neighbour has it. I also had to say good by to a couple of decent sized shade trees I was cultivating that were by the property line because he used Round Up on it. Round Up and heavy cutting made it go dormant for one year, but it killed the trees. I do not recommend Round Up. It's just as easy to cut the stuff as it is to cut it and then apply the Round Up, and once you have applied Round Up there will be an enormous number of plants that will no longer ever grow in that soil.

The surest method to eradicate knotweed is to lay concrete and build a shed that covers the entire patch. That, of course is a nuclear option, but half measures could be considered. If you can cover the ground so there is absolutely no light on it, the plant won't come up. (The roots can go through concrete but not the shoots.) If the municipality had instructed me to eradicate my knotweed stand as shown in your pictures, I would cut it all down and then cover it with something like recycled siding, or plywood. And then I would build a little deck on top of the area out of salvaged pallets, and put a bunch of large containers full of earth on top of the deck, completely covering the surface, since it would not be the kind of deck you would want to walk on, or sit on with chairs etc. In other words I would make a raised container garden on it.

If you wanted to use black plastic sheeting under the deck you could do that, but you would have to replace it sooner than the siding. However the entire deck and container garden could be removed in very early spring quite easily in order to replace the plastic on a yearly basis for as many years as necessary for the knotweed roots to die.

The plant I would replace it with would be sunflowers which I would put in the containers on the deck. Sunflowers grow about as fast as knotweed and provide a privacy screen but your neighbours will compliment you on them. Since you would be starting them a few inches off the ground and then in containers they would already have a bit of a head start.
posted by Jane the Brown at 6:13 PM on April 15 [5 favorites]


Also a gardener, also in MA. I would tell you to kill it with fucking fire but alas even that may not work.
posted by lydhre at 7:28 PM on April 15 [2 favorites]


The three Great Lies:

* The check is in the mail.
* I'm here from the government to help you.
* This isn't that running bamboo, this is clumping bamboo.

Please do not replace knotweed with bamboo. You will regret it. Much depends on where you live. My grandmother plants morning glories every year, and they cover the porch and are wonderful. She lives in Michigan. I live in the Pacific Northwest and we call the same plant "bindweed" and we can never, never get rid of it no matter how hard we try.

Good luck.
posted by kestralwing at 12:45 AM on April 16 [1 favorite]


That looks like Japanese Knotweed to me, but I'm no botanist. The one good thing about it being such a terrible invasive is that there are a ton of resources on knotweed removal and management. With such a small stand, you have the option of things like injecting herbicide into the stems instead of spraying if you have neighboring plants you are concerned about, but be prepared for an ongoing effort because it can keep coming back for a long time.

There are definitely best practices for management, which typically includes a combination of mechanical removal and herbicide. Your state extension office, Department of Natural Resources, Department of Transportation, and/or local watershed group or conservation districts should have how-to guides for removal. If not, googling a phrase like "japanese knotweed control" will get you way more results than you can possibly read.
posted by Dip Flash at 6:41 AM on April 16 [1 favorite]


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