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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. |
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picture: JKW doing a home
invasion, 3rd Street, Stamford CT. Spring 2004 |
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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: |
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picture: path along the
Mill River, Stamford CT, taken over by JKW. |
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picture: JKW in bloom,
Scalzi Park River Walk, Stamford, Ct, Summer 2003 |
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picture: JKW fall color at
Scalzi Park River Walk, Stamford, CT, Fall 2003 |
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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. |
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Pictures: Japanese knotweed
leaves, 3rd Street, Stamford, Spring 2004 |
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Picture: Japanese
knotweed’s distinctive stem, 3rd Street, Stamford, Spring
2003/ |
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picture: dense thicket
along path by Mill River summer 2003 |
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picture: winter view of
weeds along the Mill River Winter 2003 |
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picture: detail of Japanese
knotweed seeds , Mill River, Stamford CT Fall 2003 |
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