Eco-gardening is at its best in The Monday Garden
May 2, 2004, Issue 110
Out of 4000 invasive plants in North America polygonum cusipdatum has distinguished itself by making everyone’s top 10 list (except you lucky people in Zone 8 and 9; I believe that it also shuns the North Pole). Japanese knotweed, also known as Mexican Bamboo and by several unprintable epithets, is about as stoppable as a major mudslide.
picture: JKW doing a home invasion, 3rd Street, Stamford CT. Spring 2004
A knotweed, JKW’s related to jewelweed see Issue 81 buckwheat, etc. It got into North American in the late 1800’s by use of its good looks and hardiness in the garden. The havoc that it’s wrecking in our wild lands makes you think twice about any alien plant that makes seeds or fruit and is promoted as “fast growing, hardy, easy care, drought and pest resistant.”
Members of The Monday Garden “Eat An Invader Today” Club should note that the young shoots are delicious cooked and served like asparagus. (Caution: Never eat plants grown near a road, building, dumping site or driveway.) However, the yummy shoots are supported by a system of underground stems (rhizomes) that can extend out 60’ from the parent plant, sending up little JKW’s all across your lawn or favorite woodland stream bank. Its need for a root barrier (cage?) is similar to that of bamboo.
Unfortunately, the seeds, which mature in autumn, are spread long distances by the wind and don’t have little root-cages attached. So it’s germinate, colonize, make seeds, get wind borne, germinate, colonize, make seeds. The rapidly spreading JKW stands are so thick that nothing else has a chance. Soon, a colonized area looks like this:
picture: path along the Mill River, Stamford CT, taken over by JKW.
picture: JWK in bloom, Scalzi Park River Walk, Stamford, Ct, Summer 2003
picture: JKW fall color at Scalzi Park River Walk, Stamford, CT, Fall 2003
This no noxious lawn-weed; it’s a certified invader of our precious wild lands.
HOME DEFENSE:
• First, don’t buy plants that can become invasive, and don’t harbor them in your yard.
• Next, exercise vigilance: learn to identify the bad guys and get the babies before they get established.
• Third, contain existing colonies by preventing further root spread and by keeping them cut back to prevent seed formation.
Yeah, but how do you then get rid of a colony like the one in the top picture? A very small clump can be dug up BUT if you don’t get every bit of root, each bit will become a new plant. Also, when you disturb the soil, all the buried seeds get a chance to germinate. There was an army like this way back in ancient myths: slay one solider and a hundred new ones spring up.
So, what to do? Well, the traditional remedy, short of chemical warfare (which isn’t all that effective against JKW anyway), has been to repeatedly cut JKW to the ground. However, this can take years, and the JKW can probably out last you. Donna Ellis from UConn’s Department of Plant Science, who’s a member of the Connecticut Invasive Plant Working Group had an interesting recommendation for my at Master Gardeners’ program . The new suggestion: cut the JKW to the ground in the spring and cover the area with black plastic or shade clothe for the season. The sun heats the plastic and kills everything underneath, including the JKW’s roots and seeds. The following year, you can replant the area , hopefully with non-invasive natives that provide wildlife food and habitat.
Pictures: Japanese knotweed leaves, 3rd Street, Stamford, Spring 2004
Picture: Japanese knotweed’s distinctive stem, 3rd Street, Stamford, Spring 2003/
picture: dense thicket along path by Mill River summer 2003
picture: winter view of weeds along the Mill River Winter 2003
picture: detail of Japanese knotweed seeds , Mill River, Stamford CT Fall 2003
Photo credits: Sue Sweeney
© Sue Sweeney 2005
Comments (3)
What the readers said
I remember my brother had a riverbank full of this outside his house in Oradell, NJ. The dense root structure is great for stabilizing steep river banks if you don't care about choking out everything else (and he didn't). And great for growing under heavy shade. But yes, a constant battle to keep it from spreading into actual "garden" space. Gregg (NY)
That was so interesting about the knotweed -- There's a picture in the paper today of someone chopping it down at Rosa Hartman Park.. I love the idea of chopping and covering with black plastic. For small areas, that is very easy and practical. Liz (CT)
I actually have this in my backyard and have been trying to get rid of it for 5 years now. No matter how much I pull, they seems to come back stronger, taller and for some reason the roots deeper. Thanks for the tip... I let you know if it works!!!. Jennifer (NJ)
Posted by sue sweeney | April 17, 2005 5:37 PM
Posted on April 17, 2005 17:37
I work and live in Louisville Ky. I recently found this horrible plant trying to establish at an Historical property along the river. I cut it back and treated with Roundup. The black plastic sounds like a better approach.
Posted by Lisa | April 28, 2006 2:36 PM
Posted on April 28, 2006 14:36
Lisa-- If you're going to use chemicals, do a quick web search first -- the risks involved just aren't worth it -- we're better off with the plant or bug.
They are doing black plastic trials on Japanese Knotweed in at a park in my town right now; let me know how it works for you. Also check the DLT-100 ("Dandelion Terminator") -- I did an article on it 2 weeks ago and am dying to find time to take one to a mess of JKW and and see what it'll do for the roots. My town's also trying this on the JKW as part of the local trials.
Sue
Posted by S. W. Sweeney | May 1, 2006 1:57 PM
Posted on May 1, 2006 13:57