top of page

About Japanese knotweed

Japanese knotweed, Fallopia japonica, is a rampant plant that is considered an invasive weed. Its creeping roots and tall, bamboo-like stems can quickly take over a space. The roots of Japanese knotweed can grow 1m deep, making them extremely difficult to dig out, and the plant can grow through cracks in brickwork and pipework. It is against the law to allow Japanese knotweed on your land to spread onto other people's property or into the wild.

IMG_0167 (002).jpg

About Japanese knotweed

Japanese knotweed, Fallopia japonica, is a pervasive garden weed. Its creeping roots and bamboo-like stems with large, heart-shaped leaves can quickly take over its growing space. Removing Japanese knotweed can be difficult, earning it its reputation as one of the most troublesome garden weeds. Homeowners should be particularly wary of it, as the presence of Japanese knotweed in the garden can deter potential future buyers and lead to banks refusing mortgage applications.

Japanese knotweed was introduced to Britain by Victorian plant hunters in the 1800s. It was grown as an attractive ornamental garden plant, prized for its exotic appearance, heart-shaped leaves and attractive flowers, which resemble those of astilbe or goatsbeard. However, its rampant growth quickly made it unsuitable for garden cultivation. It's now an offence to cause Japanese knotweed to grow in the wild, either by means of fly-tipping or allowing the plant to escape the confines of your garden.

What is Japanese knotweed?

Japanese knotweed, Fallopia japonica, is a rampant plant that is considered an invasive weed. Its creeping roots and tall, bamboo-like stems can quickly take over a space. The roots of Japanese knotweed can grow 1m deep, making them extremely difficult to dig out, and the plant can grow through cracks in brickwork and pipework. It is against the law to allow Japanese knotweed on your land to spread onto other people's property or into the wild. 

A herbaceous perennial weed, Japanese knotweed grows in large clumps of tall, bamboo-like canes with purple spots, up to 2.1m high. From these stems alternate, light green heart-shaped leaves appear, followed by hanging clusters of creamy white flowers. The leaves are 14cm in length and the flowers grow to 15cm in length. From late autumn the plants become dormant and the canes die and lose their leaves. The dead canes often remain standing – sometimes they can take years to decompose.

In spring, look out for fleshy, reddish shoots growing on their own or among dead bamboo-like canes. New canes, leaves and flowers grow from these shoots.

Japanese knotweed may be confused with other plants, including Russian vine, Fallopia baldschuanica. While the flowers and leaf shape are similar, Russian vine has narrower, almost-arrow-shaped leaves and a much more scrambling habit than Japanese knotweed. The lack of tall stems is the most obvious identifying factor. Himalayan honeysuckle, Leycesteria formosa, is also confused with Japanese knotweed. However, on closer inspection, you will notice that Himalayan honeysuckle has opposite leaves (the leaves emerge at the same point on either side of the stem), not alternate leaves. The long, purple and white flowers are very different, too. Some species of persicaria have similar-shaped leaves, but they tend to be more narrow and don't have the bamboo-like growth of Japanese knotweed.  

Japanese knotweed can sprout from tiny sections of root. It’s extremely vigorous and can quickly spread around your garden and into other gardens. Its roots are known to exploit cracks in brickwork and pipework, and it can even damage roads. If you spot Japanese knotweed growing near your house you should eradicate it immediately, as it could potentially damage the foundations of your home.

Japanese knotweed can sometimes grow from seed, too. This means that if Japanese knotweed is growing in a neighbouring garden it will very likely come into your garden, either by its spreading roots or by seed. Keeping an eye out for early signs of growth can therefore help you remove Japanese knotweed quickly, and keep further outbreaks under control.

Japanese knotweed and the law

Schedule 9 of the Wildlife and Countryside Act 1981 makes it an offence to cause Japanese knotweed to grow in the wild, either by means of fly-tipping or allowing the plant to escape the confines of your garden.

While it’s not illegal to grow Japanese knotweed in your garden, it is illegal to allow it to spread into wild areas or neighbouring gardens, therefore it’s best practice to eradicate or at least control its spread. What’s more, if you're selling your property then you will need to remove it. Since 2013, homeowners selling their property are required to check their gardens for Japanese knotweed and declare its presence, as well as provide details of a management plan for its eradication.

If you're buying a property and Japanese knotweed has been found to be growing there, your mortgage lender may require assurances that a management plan for its eradication is in place. Regardless of whether it has been declared or not, it’s important to check for yourself, to avoid any problems later on.

Under the Environmental Protection Act 1990, Japanese knotweed is classed as 'controlled waste. This means it’s illegal to add it to home-compost or council-run garden waste bins. You are permitted to burn the waste (ideally after allowing it to dry). Alternatively, you will have disposed of it at a licensed landfill site.

bottom of page