‘We don’t know exactly how the plant found its way here from Japan. What we do know is that it thrives in Europe,’ explains project manager Laurence Koetsier. Starting from 3 August 2020, Koetsier is set to spend three weeks supervising the removal of the weed. ‘The reason why we waited before removing it is because the plant is growing at the end of Christian Neefestraat near the A10, where there’s no one living for it to bother them. But since we now intend to prepare the land for construction, it’s time to get rid of the Japanese knotweed.’
Removal of Japanese knotweed
To say that Japanese knotweed is rampant is an understatement. Despite its relatively unassuming name, this species of plant can leave a trail of destruction in its wake. Laurence Koetsier: ‘After removing it, we even have to have the soil cleaned.’
Strong and persistent
In the future, there will be apartments on this site. The provisional design will be completed later this year and construction starts at the end of 2021. Koetsier: ‘So that will take a while. The main focus now is on the Japanese knotweed and we need to remove it very carefully, so that it can’t wreak any more damage later on.’ The problem is that the plant grows incredibly fast, is very persistent and strong. ‘Knotweed grows through anything and can cause damage to street tiles, foundations, houses, cables, pipes and drains.’
Removing the plant is also far from simple. ‘If just a millimetre of root is left behind, the plant can regrow just as quickly’, explains Koetsier. ‘That’s why we’re digging up this area of around 300 sq. m. to a depth of 1.5 m, up to the point where the groundwater starts and the plant can’t take root. We’re also applying a wide margin, so we’re absolutely sure that there will be no bits of knotweed left here when we’ve finished.’ The soil that is removed is dealt with very carefully. ‘When you normally dig up soil, it just goes to a soil bank for companies to use. Not in this case. It’s carefully cleaned before being taken there.’
The fact that Japanese knotweed is not a very popular neighbour is proven by the fact that the city council has a special team for removing and identifying it. Koetsier: ‘It might sound a bit extreme; there are also some places where the plant can’t cause so much damage. But when it does, it needs to be very carefully removed.’ This map shows where Japanese knotweed is still to be found in Amsterdam.