J
apanese knotweed is a plant caught up in the polariza-
tion of our times. Both its virtues and its malevolence have been
inflated in the public imagination, and it is at once known as both
miracle drug and botanical monster. In Canada, a nation not prone to
paranoia, knotweed has been described as "a demon weed so relent-
less, bloody-minded and destructive, it's been called the terrorist of the
plant kingdom." Strong words for a creature with no teeth, claws, or
toxicity to humans. Internet herbalists tout its miracle cancer-fighting
properties with equal hyperbole. Yet, with this plant, the quiet facts are
more interesting than the hype.
Brought to Great Britain and the U.S. from its native Japan as an orna-
mental perennial in the late 19th century, knotweed behaved itself in
backyards and botanical gardens until the 1930s, when it escaped the
garden gate and set about colonizing. It now grows just as happily in
roadside drainage ditches and construction dumpsites as it does along
woodland margins and streambanks.
The plant's hollow, arching canes can grow 3 inches (8 cm) in a day. Its
rhizomes send out runner shoots in all directions so that, like bamboo,
an individual knotweed plant can quickly grow into a dense thicket.
Its
Japanese knotweed
(Polygonum cuspidatum; Latin
synonym Fallopia japonica) is
indisputably a major nuisance
in the urban forest, including
that of the most populous
city in the U.S. NYC Parks
Natural Resources Group
has documented extensive
research and control methods
they've used, in partnership
with the Bronx River Alliance
and other entities, to combat
knotweed along the Bronx
River and in other natural
areas in the City's five bor
-
oughs. Their strategy involves
a combination of mechanical
and chemical means.
Control of Japanese knot-
weed is widely acknowledged
to be imperfect at best. While
we can and should manage
its presence in our urban for-
ests, this plant is here to stay.
Why and how is it so suc-
cessful at colonizing the most
degraded sites? Why is it so
hard to control? And what
are some of the positive attri
-
butes you might not have
heard about? In this piece,
Laura Wyeth, a horticulturist
with a particular interest in
the adaptability of weeds,
explores some of what makes
Japanese knotweed unique.
(right) The author with the dreaded (and fascinating) Japanese knotweed.
Knotweed 360°: Bad Actor in the Urban Forest
(with Some Redeeming Qualities)
By Laura Wyeth, Horticulturist
Laura Wyeth is a Horticulturist with
15 years' experience in the field and
a special interest in the evolutionary
adaptations of weeds.
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