Invasive Species Week: Japanese Knotweed

What?
Japanese Knotweed was introduced to the UK as an ornamental plant but has spread extensively in the wild. With its rapid growth of more than 20mm a day, it forms dense clumps over 3m high which crowd out and prevent the growth of native plants.

The rhizome root system, from which new plants grow, can extend several metres away from the original plant and be up to 2m deep. The plant spreads so rapidly not only through progression of its root system but because any fragments of its stem or root will grow to form a new plant (a piece as small as 0.8 grams can regenerate). This makes it a very difficult plant to eradicate.

Japanese Knotweed will grow in any type of soil no matter how poor and is often found along railways, riverbanks, roads and particularly on derelict sites.

Identification
Japanese Knotweed forms dense clumps and grows up to 3 metres tall.
The stem is hollow with distinct nodes like bamboo and breaks easily. In Spring it is fleshy and red tinged and in
Summer it is green with purple speckles.
Leaves in Spring are pinky red and uncurl as the stem grows. In Summer they become large oval or heart shaped
mid-green.
Flowers are cream coloured and appear in drooping clusters towards the end of August.
The plant dies before November often leaving behind the upright brown, hollow, woody stalks.
Why?
• Avoid environmental harm: Japanese Knotweed
shades out native plants by producing a dense canopy
of leaves early in the growing season. Although
Japanese Knotweed is not toxic to humans or animals, it
offers a poor habitat for insects, birds and mammals.
• Avoid prosecution: It is illegal “to plant or otherwise
encourage” the growth of Japanese Knotweed. This
could include cutting the plant or roots and disturbing
or moving surrounding soil which may contain root
material unless as part of an eradication process.
DO
3 Immediately STOP all work
within 7 metres of the suspect
plant and contact your line
manager for instructions if
you think you have identified
Japanese Knotweed on your
site.
DON’T
7 Excavate or move any soil from
within 7 metres of a Japanese
Knotweed plant without instruction.
7 Track plant or vehicles over the
area.
7 Stockpile potentially contaminated
material within 10 metres of a
watercourse or drain.
TILHILL Forestry
Toolbox Talk
TT/05 Version 4 – February 2016 1 of 1
SF/09 Version 1
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TT05 Japanese Knotweed