Guidance on the control of Japanese knotweed
What is Japanese knotweed?
Japanese knotweed (fallopia japonica) is a native plant of
Japan, Taiwan and Northern China. It was first introduced to the UK
in the early 1800s as an ornamental plant.
What does it look like?
It is a vigorous perennial plant that can grow in excess
of three metres in height and is commonly seen on riverbanks
and wasteground. When Japanese knotweed colonises areas, the plant
forms dense thickets that die back to dead, rigid stems in the
winter, only to re-grow more vigorously the following growing
Why is Japanese knotweed a problem?
In the UK, Japanese knotweed has no natural predators or
controls. Consequently it has been able to colonise areas
throughout the British Isles. The lack of natural controls has
resulted in a number of problems including shading out other native
species, the accumulation of litter amongst the stems, riverside
erosion when knotweed dies back and damage to pavements, buildings
and car parks as knotweed is able to grow through asphalt.
Japanese knotweed grows vegetatively, spreading by means of
underground stems or rhizomes that push through the soil and put up
aerial shoots periodically. When broken off, very small fragments
of rhizome (as little as 2.5cm/1 inch in length) can form new
plants. Rhizome fragments are also viable for a long period of
time. For these reasons, and since Japanese knotweed has no
particular habitat preferences in the UK, this plant is a major
Is it an offence to allow Japanese knotweed to grow in the
Japanese knotweed has a number of closely related sub
species which also form hybrids, all of which come under the
provisions of the Wildlife and Countryside Act (1981) which states
that 'it is an offence to plant or otherwise cause the plant to
grow in the wild.' Furthermore, the Environmental Protection Act
(1990) classes Japanese knotweed as 'controlled waste' and
consequently should be disposed of at a licensed landfill site
under the EPA (Duty of Care) Regulations (1991).
How can I control Japanese knotweed?
There are various approaches used to control it. Primarily,
these comprise spraying and cutting or a combination of both. Where
appropriate, grazing may also be a management option. Another
alternative is covering the Japanese knotweed with a membrane and
over-planting with a quick-growing species such as willow.
How can I control Japanese knotweed on my land?
If Japanese knotweed is regularly pulled up or cut, the plant is
weakened and over a number of years will begin to die off. If
feasible, a good way of disposing of the plant once pulled or cut
is to thoroughly burn it. However, unless you intend to take the
plant remains to a licensed landfill site, the Japanese knotweed
must be kept on site, otherwise a breach of the above legislation
will have occurred.
Another alternative is to apply a herbicide. One of the most
common herbicide applications for the control of Japanese knotweed
and other invasive plants such as Himalayan balsam, is a herbicide
that contains glyphosate as an active ingredient. Glyphosate is
what is known as a non-specific herbicide, which means it will
affect most plants to which it is applied. Therefore, care must be
taken when applying glyphosate based herbicides if the treatment is
close to sensitive areas. Glyphosate used for domestic use can be
purchased from garden centres and retailers under a number of names
including Roundup, Tumbleweed and Tough Weed Gun.
The effectiveness of the herbicide is dependent on the amount of
Japanese knotweed that needs to be treated. If you wish to treat
large stands of Japanese knotweed you may wish to consult a
contractor. If you consider that the area of Japanese knotweed that
needs treating is manageable, you may wish to consider a
combination of cutting and spraying in early summer followed by
spraying again in late summer.
Whichever management approach is decided upon, regular
monitoring of the area should be undertaken to ensure the knotweed
is not spreading elsewhere or contaminating watercourses.
Where can I dispose of Japanese knotweed?
Japanese knotweed and soil containing it are classed as
'controlled waste' under the legislation referred to above. This
means it can only be disposed of at licensed landfill sites. The
nearest waste disposal site licensed to accept Japanese knotweed
Biffa Waste Services, Trecatti Landfill Site, Fochriw, Nr
Dowlais, Merthyr Tydfil, CF48 4AB
Telephone no. 01685 721882 / Fax no. 01685 387285.
- Will need a minimum of 24 hours notice to arrange
- Minimum charge of three tonnes plus a proportion of the
landfill tax depending on weight.
- Trailers to be covered during transit with small quantities to
be securely bagged up, not loose, and drivers to ensure vehicle is
empty and clean before leaving site.
What other factors in relation to Japanese knotweed should I be
- The Vale of Glamorgan Council and Environment Agency Wales are
not obliged to control Japanese knotweed on behalf of other
- It is the landowner's responsibility to control Japanese
knotweed on their land if it is affecting neighbouring land.
- If treating Japanese knotweed near watercourses, the
Environment Agency Wales will need to be contacted on 08459 333
- The persistence of Japanese knotweed rhizomes makes the plant
hard to eradicate. Therefore, be aware that you will need to treat
it for a number of years, even though you may think you have killed
it after the first treatment.
- Early identification and treatment of Japanese knotweed will
save money and time in the long term as the plant is only beginning
to establish and will be less vigorous compared with when it is
- Licensed Japanese knotweed sprayers must have a current
National Proficiency Test Certificate. For knapsack spraying, these
certificates are PA1 and PA6 or equivalent.
- Mowing and flailing Japanese knotweed will cause it to
- Do not compost or chip Japanese knotweed.
Who can I contact for more information?
If Japanese knotweed is growing on Council land in the Vale of
Glamorgan, please contact the Council's call centre on 01446
When growing near a watercourse or river contact the
Environment Agency Wales on
08459 333 111.