Japanese Knotweed: Your Questions Answered

Japanese Knotweed has received nothing but bad press over the years – and with good reason. It is a destructive weed that was introduced to this country in the 1800s and actively planted by local governments to strengthen river and railway embankments.

Now, its ability to dominate local species and undermine buildings and other underground structures is well known. Here we tackle some of the common questions relating to Japanese Knotweed, its treatment and the financial implications.

What is Japanese Knotweed and what problems can it can create?

Japanese Knotweed is a fast-growing non-native species with very strong and far reaching roots. During the spring-summer period it can quickly grow to over 6 feet high and dominate nearby plant life. However, the weed does most damage under the ground with its roots. If left untreated it can damage foundations, walls, and drainage pipes. The weed is hard to kill and requires specialist approaches to ensure it is eradicated.

How can we identify Japanese Knotweed

Japanese Knotweed does have distinctive features that separate it from many other plants, but it can look similar to other types of knotweed that are less destructive, or even entirely unrelated plants such as Dogwood. A good description of the weed from Scottish Field is below, but it is always advisable to ask a specialist to give their opinion.

“It normally has green leaves, but new leaves are dark red, rolled at the edges and around 1-4cm in length. Young leaves are green with red veins, the edges may be slightly rolled, and the length is between 4-8cm. Mature leaves are green, heart or shield-shaped and around 12cm in length, the base of the leaf is usually flat. Early season shoots and stems are fleshy but soon form a vertical green bamboo-like appearance with red rings and nodes.”

Is Japanese Knotweed Poisonous?

No, this is a common misconception but the plant is not harmful to people. It’s not known conclusively whether the plant is harmful to pets if eaten, so it is advisable to keep pets away.

How is Japanese Knotweed removed?

There are two primary approaches: either to dig out the ground where the weed is situated (to a depth of up to 3 metres) and dispose of the earth at a specialist landfill site, or by chemical treatment over several years. In either case a specialist company would be used. Digging out is not a practical option for many properties, the weed’s roots may have spread under buildings or other hard landscaping or even to neighbouring properties. The more common solution is to use a chemical treatment and spray the leaves and into the hollow stems of each plant. This treatment must then be repeated over several years until the is no further sign of the plant.

Does the presence of Japanese Knotweed affect me gaining a mortgage?

Whilst the process for treating Japanese Knotweed has become more reliable and efficient over the years, mortgage companies are still wary about lending when the weed is present. The degree of risk to the property, mainly based on how close the weed is to the property, is the lender’s prime concern. In the first instance, the seller of the property is required to specifically state whether Japanese Knotweed is present, as part of the TA6 form. If the weed is present, the seller must also provide a management plan for its treatment. The surveyor’s report will also guide the lender’s decision – in the worst case, if the presence of the weed is significant and close to the property, they could state that the property is not suitable for mortgage purposes.

Who pays for the treatment if Japanese Knotweed is found on our grounds?

This can depend on where the weed is situated and how it spread to the site. If the weed has obviously spread from a neighbouring property, the law would be on your side to require the neighbour to pay for the treatment. However, proving the source of the weed can be difficult and speed is of the essence since the plant can grow at a rate of 2-4cm a day. It may therefore require your property to take responsibility for treating the problem initially, and then seek reimbursement from the neighbour after the fact.

If the weed has not obviously spread from a neighbour, then payment for the treatment would typically come out of the property’s service charge. In some cases, where the weed is found on a boundary, the cost of the treatment may be shared between your property and the neighbour as you would both have a vested interest in a quick resolution.

If you see a plant on your property’s grounds that you believe could be Japanese Knotweed, you should contact your management company immediately. They should then quickly respond by arranging an inspection to confirm the plant’s species.

Ask A Question