If you have found Japanese Knotweed on your property, you may be wondering what to do next. Most importantly, you’ll need to understand what the potential damage and costs could be to your property, and the potential impact Japanese Knotweed will have on a mortgage.

Several news reports in recent years have fueled fears of Britain’s most invasive plant. As a result, members of the public have attempted to remove their Japanese knotweed themselves. This is a mistake. If you spot knotweed in your garden, there are a few important guidelines you should take into consideration. Under no circumstances should you attempt to remove knotweed yourself. 

It is not illegal to have knotweed on your property, but irresponsible behaviour resulting in the spread of knotweed into neighbouring properties can earn you an ASBO, which can result in fines of up to £2,500. 

What is Japanese Knotweed?

Japanese Knotweed is a very invasive, fast-growing plant that can grow at a rate of 10 cm per day. Its ability to grow aggressively can result in costly damage to property and infrastructure.

Japanese Knotweed (Fallopia japonica) is native to Japan and was introduced as an ornamental garden plant in Victorian times. It grows rapidly, quickly smothering other vegetation and aggressively colonising any soil it is allowed to thrive in.

The non-native weed spreads quickly, with its bamboo-like stems and large light green leaves reaching 2m in height, along with an intricate network of underground rhizomes, which make it a difficult species to eradicate. Simply pulling the plant upwards will not stop the spread, and may in fact cause it to spread even faster.

Japanese Knotweed in garden areas

The presence of Japanese Knotweed in a garden can seriously affect the value of your home, as well as the chance buyers have of getting a mortgage accepted. 

Japanese Knotweed’s strong and sturdy plant structure means it can thrive in a wide variety of growing conditions. Soil pH or salinity has little impact on plant growth rate, with Japanese Knotweed surviving in temperatures as low as -35 ° C. 

The damage caused by Japanese Knotweed in garden areas can be extensive, with these plants often managing to spread to neighbouring properties too. They can exploit holes in concrete and brick, take root and cause structural damage to patio areas, retaining walls, and even driveways. 

Their root systems grow profusely, growing up to three metres deep and up to seven metres wide. Its ability to grow up to 10 cm per day in summer means it can quickly and easily overwhelm surrounding plants, and threaten properties. 

Japanese Knotweed inside house & building foundations

Japanese Knotweed is known for destroying the foundations of buildings. The most notable case of this was reported by the BBC in 2011. Shortly after discovering Japanese Knotweed in their back garden, property owners were alarmed to find that not long after, the weed had grown through the skirting boards of their dining room. Experts estimated that the value of their property had since dropped from £ 305,000 to £ 50,000 and that their knotweed infestation had made it impossible to sell their home.

Although the foundations of the property weren’t necessarily damaged by the Japanese Knotweed, the infestation under their home made paying for the removal an expensive prospect. Experts advised that the only way they could ensure the plant was completely removed from the property would be to demolish the entire structure and dig up the 3 metres (10 feet) of contaminated soil below.

A guide to reporting Japanese Knotweed

You should always report Japanese knotweed if you think it is harming your local environment and may not yet have been identified by local authorities, or if you think it may soon invade your property. Although the law doesn’t require you to do so, reporting Japanese knotweed to the proper authorities can help the government keep tabs on the ongoing threat posed by this invasive plant.

If Japanese Knotweed is found on your own property, you are not legally obliged to report it, however, if you plan on selling your house you will be legally required to notify the buyers of any Japanese Knotweed which is present on your property.

Do you need to inform your estate agent about Japanese Knotweed?

Planning to sell your property? If you discover Japanese knotweed on your property, you should report it to your real estate agent as soon as possible. If you’re considering selling a home that has Japanese knotweed growing on it, be as open as possible with your real estate agent about the situation. 

When your real estate agent has access to all the information about your property, you are more likely to sell it faster. You are required by law to disclose Japanese Knotweed on your property, so if you don’t tell them about the infestation, you run the risk of jeopardising future sales as well as your business relationship with your agent.

Final Thoughts: Take control with a professional survey

If Japanese Knotweed spreads to neighbouring properties, you will be held liable. It is a highly invasive species with a high damage potential, and many mortgage lenders require sellers to have a full Japanese Knotweed removal plan in place. 

If you suspect you have Japanese knotweed on your property, it is important to conduct a Japanese knotweed survey to determine the extent of the problem, and the best method of treatment for your property to ensure you remain compliant and avoid being liable for extensive costs in future.