Controlling Japanese Knotweed with Root Barriers

Root barrier membranes can be used to prevent encroachment or to protect specific surfaces such as asphalt, driveways, etc.

When to use vertical root barriers 

Vertical root barriers are typically used at boundaries to prevent encroachment to or from adjoining land. They are installed to a depth of 2-3 metres depending upon the depth of the knotweed rhizome. 

A trench is dug with a mechanical excavator. The root barrier membrane is positioned in the vertical plane as close to the boundary as possible. Finally the trench is backfilled with appropriate fill material, with particular care being taken to avoid damage to the membrane.

Installing vertical root barriers is an expensive operation, normally only justified where other excavation operations are taking place. It is seldom economic to install root barriers where herbicide treatment is employed.

When to use horizontal root barriers

Horizontal root barriers can be used to protect specific surfaces such as roadways, drives, etc. where it has not been possible to remove all Japanese knotweed rhizome. The root barrier simply forms a barrier, which actually encourages more lateral spread. A sacrificial zone is usually provided at the edge of the root barrier, such that if new growth does appear it can be treated with herbicide.