German Federal Agency for Nature Conservation (BfN)


Animal, plants and fungi

Historical spread of Asiatic knotweeds (Fallopia spp.) in Germany

Asian knotweeds continuing to spread and cause major damage

Asian knotweeds continue to spread in Germany. They cause a range of ecological and economic damage, making them one of the highest-cost alien species today.

The Asian knotweeds Fallopia japonica and F. sachalinensis were deliberately introduced to Central Europe as a park and garden plant in the 19th century. A hybrid of the two, Fallopia bohemica, has additionally existed since the early 1990s. The three knotweeds have spread throughout Germany over the last few decades. Alongside active planting as ground cover, a fodder plant for livestock and game and for green embankments, its rapid spread is accounted for its ease of propagation from stems and roots (rhizomes): a rhizome fragment just 1.5 cm long is enough to start a new thicket. The plants rapidly colonise the length of roads and watercourses and invade natural ecosystems such as floodplains.

Knotweeds endanger biodiversity

Due to their thick growth, knotweeds often form impenetrable thickets that exclude other vegetation, take light from other species, and can also crowd out species such as the specially protected ostrich fern. Asian knotweeds are thus classified as invasive alien species that endanger biodiversity in Germany. Due to their massively vigorous growth, they can also damage flood defences and masonry. They can easily penetrate 5 cm of asphalt.

Further spread of invasive alien species must be prevented

As removing widespread invasive neophytes is both difficult and labour and cost-intensive, such action only makes sense in limited numbers of cases, such as in particularly sensitive sites. It is therefore all the more important to prevent the emergence of new populations and the further spread of invasive alien species. This means no new planting of invasive alien species, no disposal of plant material in the countryside, and no transportation of contaminated soil.