Beware of Japanese knotweed’s winter hibernation

The Japanese knotweed growing season ends in late autumn and, like many perennial plants, its above-ground growth dies back. But despite looking dead, knotweed is replenished with new energy reserves from the summer growth which are drawn down and stored in its powerful underground rhizome system, ready to re-emerge stronger next spring.

After the first frost, knotweed’s heart-shaped leaves turn yellow and fall to the ground. Its bamboo-like canes lose their green appearance and start to turn brown and brittle – although most will remain standing. The distinctive crown will still be visible, but no fresh growth will appear until the ground begins to warm in the spring, usually around March or April. Environet has a free ID Guide that is full of  tips and pictures to help identify knotweed during winter.

Homebuyers beware

Homebuyers should be especially vigilant when viewing properties during the winter months, when property owners may be tempted to take advantage of the plant’s hibernation which makes it much easier to conceal. Failure to disclose the presence of knotweed could lead to a costly legal claim for misrepresentation when the plant regrows.

Is there Japanese knotweed in your area?

If you are looking to buy a property and are concerned about the presence of Japanese knotweed, take a look at Environet’s interactive map, to see if you are potentially buying or selling in a high risk area. The map was designed to inform homeowners and homebuyers of the local presence of knotweed and the potential risk to their property. Data is generated from over 50,000 known infestations, with new sightings added daily.

What to do if you have concerns?

If there is evidence of Japanese knotweed nearby, booking a survey by a professional team is the best option. The survey company will first look for visible signs of the plant. It is good to be aware that any full survey for Japanese knotweed, needs to consider the extent of the rhizomes underground and how far these have spread. The survey team will also look at the potential source of the infestation, confirm whether any damage has been caused and whether the knotweed is active or dormant. Once the survey has been completed, a tailored management plan will be put together for you.

Don’t wait for spring!

Come spring, when the ground temperature begins to warm, knotweed will emerge and begin to grow rapidly. But there’s no need to wait until then to deal with the problem. Herbicide treatment cannot be carried out during the winter months, since it requires the plant to be in leaf, but there are very effective, cost-efficient treatments that can be undertaken through the autumn and winter with excellent results, allowing gardens to be fully operational during the summer months. One method involves excavating the bulk of the knotweed rhizomes from the ground, reducing the plant’s vigour and stimulating growth, enabling any new shoots that emerge the following spring to be herbicide treated.

Free invasive plant checker

Environet offers a free ID service for anyone who has a suspicious plant in their garden and wants to check if it’s knotweed, which is commonly mistaken for ivy, bindweed and Russian Vine. Just email a photo to expert@environetuk.com.