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Japanese knotweed was introduced to the UK in the 19th century as an ornamental garden plant. It had been used in Japan to stabilise sand banks and there have been suggestions that it was similarly employed to stabilise embankments in the UK.

Lacking the competitors, diseases and animals that keep it in check in its native range, knotweed’s uncontrolled and invasive nature quickly allowed it to become a pest in the UK. As only female plants were introduced, no pollen was available from male plants to allow fertile seeds to develop. Consequently, almost all knotweed in the UK has spread from small fragments of plant material (mainly roots) that have been transported to new locations in knotweed-contaminated soil.

Knotweed grows rapidly underground and pushes up annual shoots each spring. The roots and shoots are capable of exploiting gaps in buildings and hard surfaces such as concrete and tarmac, which can cause significant damage to them over time. The root system of knotweed can be very deep (a few metres) and spread several metres from the aboveground stems.

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