tissues have remarkable powers of regeneration; a piece of
broken stem or rhizome the size of a thimble can resprout
into a new plant, and this often happens when soil con-
taining pieces of rhizome is transported. Consequently,
knotweed is often seen growing in construction sites
where topsoil has been brought in from elsewhere. It
soldiers on through crummy soil and can sprout through
small pavement cracks and push its way through asphalt.
Try to dig one out, and three will take its place.
Knotweed laughs at pesticides. Its only predators, a
few insects and one or two fungal diseases, have not
followed it from Japan, and so its spread is unhindered.
It is now considered highly invasive throughout the
U.S., Canada, and much of Europe.
Japanese knotweed is such an issue in Britain, where
it enjoys a longer, milder growing season than in the
U.S., that companies in almost every British county spe-
cialize in trying to eradicate it and an equally numerous
"I think urban foresters
should be familiar with all of the
common plants in their local urban
ecosystems (for better or worse),
because we must constantly prior-
itize problems and allocate finite
resources. Understanding the eco-
logical effects of invasives helps us
do that better. I have seen Japanese
knotweed in lots of places but was
unfamiliar with much of what's in
Laura's article."
—Steve Cothrel, Parks and Forestry
Superintendent, Upper Arlington, Ohio
Japanese knotweed flowers are used by bees for nec-
tar, producing a dark "bamboo honey" considered high
in quality. Photo by Jan Samanek, State Phytosanitary
Association, bugwood.org
www.urban-forestry.com 17
