Soil containing Japanese knotweed material may be buried on the site where it is produced.
Prior to burial of the Japanese Knotweed you should apply a non-persistent herbicide such as Glyphosate, this should reduce the growth of the viable material. (Checking on the product label it will inform you of the active period of the herbicide; it is advised not to bury the treated material during this time.)
The Japanese Knotweed should be buried in a 5m deep burial pit; the Knotweed is then placed in the pit to a depth of 3m, and then covered with a permeable membrane with a 2m capping covering the membrane.
In some cases it’s not possible to bury the Knotweed 5m deep. If this is the case the Knotweed can be buried at 3m deep but then completely encapsulated into a root barrier membrane cell.
When you excavate your burial pit to a depth of 3m it should be lined with a membrane material, this should then be covered with sand to prevent any machinery puncturing the membrane whilst back filling with Knotweed. You should allow an overlap up the sides to enable you to weld the membrane together giving you totally encapsulated cell. The Knotweed should then be put into the pit to a depth of 1m, the overlap of the membrane is then pulled together to be sealed. It is important to have a minimum amount of seams, if any Knotweed does have the strength to regenerate it will breakthrough any holes or joints.
It is vital the integrity of the membrane is maintained at all times.
Care should be taken and plan produced of where you are going to have your burial pit, you don’t want it to be where it is likely to be compromised at a later date, try to avoid areas where service trenches are to be laid or any other activity likely to tear the membrane.
Accurately map and advise the local Environment Agency office of the record showing the location of the burial site to prevent potential disturbance and possible re- infestation in the future.
Given that the Rhizomes may remain dormant for 20 years, it’s important the supplier of the membrane gives a guarantee exceeding this, minimum requirement up to 50 years.
Many root barrier membranes are available which claim to prevent Japanese knotweed penetrating. A root barrier membrane is only as good as the way in which it has been laid, expert supervision is essential when the root barrier membrane is installed.