Information About Japanese Knotweed

The climate is changing, and nature is changing along with it. You can see the effects of this in the municipality of Voorschoten as well. This is partly due to the spread of invasive plants such as hogweed and Japanese knotweed. Japanese knotweed, for example, is a tenacious plant that can cause significant damage to your garden, home, and public spaces. Learn how to identify Japanese knotweed and what you can do to control it.

Japanese Knotweed in Public Spaces

The municipality keeps track of the plants' locations on a map. Have you spotted Japanese knotweed in a public area? If so, please report it using the reporting form at . Be sure to clearly indicate the location and specify that it is Japanese knotweed. You can also attach a photo to your report. Alternatively, you can contact the Customer Contact Center by phone at 14071.

During the growing season, the municipality mows the plants once a month. This weakens the plants and prevents them from spreading further.

Overview Map

On the map, you can see where Japanese knotweed has been spotted in Voorschoten so far.

Japanese Knotweed on Private Property

Do you have Japanese knotweed on your property? If so, you can hire a landscaper or control the plant yourself. A landscaper can advise you on this. The municipality will not come to inspect the site. You can find detailed advice and an evaluation of control methods in the report by the Probos Foundation.

What You Need to Know About Japanese Knotweed

1. Japanese knotweed is an invasive alien species. An invasive alien species is a plant, animal, or other organism that is not native to the Netherlands but has nevertheless become established here, partly due to climate change.
2. Japanese knotweed dies back above ground in the winter, but blooms above ground from March/April through November.
3. The roots run deep (sometimes as deep as three meters). The stems are green with red spots and hollow inside. The stems resemble bamboo.
4. Japanese knotweed grows at an astonishing rate. First, you see small red buds and leaves, and shortly afterward, the stems shoot up out of the ground. In the summer, the leaves turn a fresh green and grow as large as your hand. White flowers appear at the tips of the stems. The plant can grow up to two meters tall.
5. Japanese knotweed is beautiful, but dangerous. It crowds out other plants, and its tremendous growth potential causes damage to bike paths, paved roads, and the foundations of buildings and homes. All it takes for the plant to invade your home is a small crack or hole.
6. Early removal is therefore of the utmost importance—not only for your own yard and home, but also for public green spaces and outdoor areas.

What You Can Do Yourself to Control the Plant

1. Digging up
   It is important to remove all the roots. Even the smallest piece of Japanese knotweed can grow into a new plant.
2. Mow and keep mowing
   If digging it up isn’t working because the roots are already too deep, pull out the stems and then mow as close to the ground as possible. Repeat this every two to four weeks for several months. Keep at it—especially keep mowing. Mowing will exhaust the plant, and there’s a good chance it will eventually disappear.
3. Lawn clippings = residual waste
   It is important that you remove the lawn clippings (not just the roots and loose plant debris, but also the soil in which the Japanese knotweed was growing) and dispose of them as residual waste. So do not put it in the vegetable, fruit, and garden waste (GFT) bin, but in the container for general waste. This is because of the risk that the plant could spread further through the GFT.