Frequently Asked Questions by Developers
How do we know whether we have Japanese knotweed on our site?
It is usually relatively easy to identify Japanese knotweed, particularly during the growing season April to October when it is growing at an alarming rate. See our photo gallery
to see what the plant should look like at differing times of the year.
If we can’t see any knotweed, does it mean the site is definitely clear?
No, Japanese knotweed can be hidden from view at the surface if:
- someone has intentionally cut it all back to below ground level to hide it
- temporarily covered over by hard surface, membranes etc.
- dormancy has been induced e.g. by poor herbicide treatment
- out-competed by other plant species such as bramble
What problems can knotweed cause if we ignore it?
Japanese knotweed causes significant problems, particularly on development sites. It can cause construction delays. It can cause damage to property. It can make the sale of property very difficult, thereby lowering value. For more info see our damage caused
If we know we have knotweed on our site what should we do?
You need to diagnose the scale of the problem.
This involves trying to establish the extent of land that is affected and the corresponding volume of infested soils. Depth and lateral spread of Japanese knotweed need to be estimated.
You need to determine any site specific constraints that affect the treatment options, such as proximity of water courses, ground conditions etc.
You urgently need to instigate procedures to minimise the risk of spreading the knotweed further. For example you should prevent any unauthorised access into the area, and prohibit any activity that is likely to disturb the infested soils.
You need to work out a suitable strategy for eradicating the knotweed. This will depend upon the site specific conditions, your timeframe and your budget.
What options are available to us for eradicating the knotweed?
These typically fall into two categories, the chemical methods using herbicides, and the physical methods to remove the source of the problem e.g. the underground rhizome system. For more info see treatment options
What does it cost to get rid of Japanese knotweed?
That depends upon the quantity of knotweed and the method you wish to employ. If you need a quick budget cost, please call us and we’ll be able to give you a rough idea.
What precautions should we take to prevent it from being spread further?
Knotweed is spread by moving pieces of knotweed rhizome (normally within soils) from one place to another. Commonly this occurs when plant and machinery is used on site that disturbs soil. You should therefore prevent any activity that is likely to cause soil disturbance in the infested areas.
You should mark out the infested areas with a suitable buffer zone and ideally fence it off to prevent unauthorised access into the area.
You should employ a firm that specialises in knotweed eradication to resolve the problem for you.