Asian knotweeds are invasive alien plants which pose a threat to local biodiversity
Key figures 2021
This project is supported by the Federal Office for the Environment, the Cantons of Vaud and Geneva, and the Fond Vitale Environnement SIG.
What is Japanese knotweed?
- Asian knotweeds (Reynoutria japonica, Reynoutria sachalinensis, Reynoutria x bohemica ) are invasive exotic species imported from Asia in the 19th century as ornamental plants and to provide fodder for animals.
- They have a green, bamboo-like stem and heart-shaped leaves which are slightly flat at the base. The nodes of the stems are often reddish.
- In young plants, the stem and the leaves are also red.
- Knotweed is a geophytic plant, in other words the part which is visible above ground dies down in winter, and grows back vigorously in the spring (géophyte plant).
- Knotweeds are native to Asia and are not susceptible to damage by any of the parasites, insects etc which are found in this part of the world.
- Knotweed grows very quickly (up to 8 centimeters per day and 3 meters in a few weeks), monopolising all the space available and rapidly spreading a canopy of leaves which stops sunlight from reaching the native plants.
- Knotweed is extremely difficult to eradicate. 1 cm of stem or root is enough for a plant to regenerate. Once knotweed is present in an area, whether or not it has been planted deliberately, it will spread very rapidly. Its creeping rhizomes allow massive regrowth after winter, making it the first plant to regrow in the spring and preventing native plants from establishing themselves.
- The roots of knotweed give off toxic substances which limit the development of other plants.
- Regular uprooting by hand, every 2-3 weeks during the growing season (April to October), over several years.
- Asian knotweed ( Reynoutria japonica, Reynoutria sachalinensis, Reynoutria x bohemica) are invasive perennial herbaceous plant species from the Polygonaceae family native to East Asia. They have naturalized in a wide variety of European wetlands.
- These large, vigorous plants have erect, reddish hollow stems, similar to bamboo canes.
- They are rhizomatous / erect hemicryptophyte geophyte plants. The broadly ovate-triangular lower leaves reach 15-20 cm long and are sharply truncated at the base. They are alternate.
- The small white flowers are arranged in panicles in the leaf axils.
Join us to help in the fight against this menace!
Are you keen to help us in the long-term struggle against the scourge of invasive plants?
As part of the team of volunteers working with the campaign Stop Knotweed, you will have many opportunities to participate in uprooting sessions with a group of like-minded people, reaping all the social and physical benefits of this healthy outdoors activity.
You will receive the necessary information about the types of tasks involved, the areas where the uprooting sessions will take place, and the periods of the year (April to October) during which this major campaign will be organized.
All helpers are welcome to assist us in maintaining a schedule of regular Stop Knotweed uprooting sessions, which mobilise a large number of volunteers in the cantons of Geneva, Valais and Vaud as well as in Haute-Savoie.
If your area is not listed on the form opposite, please contact us by phone or email !
asl(at)asleman.org or 022 736 86 20