How to Get Rid of Japanese Knotweed

Getting rid of Japanese knotweed is no simple task. This fast-growing invasive plant is known for its ability to spread quickly, damage structures and overwhelm gardens. Controlling it requires a consistent and well-planned approach, as even small fragments left in the soil can lead to regrowth. While eradication is possible, it often takes time, persistence and in some cases professional support to ensure the plant is fully removed and does not return.

What Is Japanese Knotweed?

Japanese knotweed is a perennial plant originally introduced to the UK in the 19th century as an ornamental species. It quickly became problematic due to its aggressive growth and ability to spread underground via rhizomes. These underground stems are capable of pushing through soil, concrete and tarmac in search of light and water. The plant is classified as an invasive species in the UK and is known for its impact on gardens, buildings and natural habitats.

How Do You Identify It?

Japanese knotweed can be identified by its bamboo-like stems, which are hollow and grow rapidly during spring and summer. The leaves are shovel or heart-shaped with a pointed tip and grow in a distinctive zig-zag pattern along the stems. The plant also produces small creamy white flowers in late summer, which cluster together on upright spikes. It often grows in dense clumps and spreads quickly if not controlled. In winter, the stems die back but remain standing as brown, brittle stalks.

What Does Japanese Knotweed Look Like?

In spring, knotweed emerges as reddish-purple shoots that resemble asparagus. As the plant matures, the stems become green with purple speckles and can reach up to two metres tall. The leaves are lush green, broad and flat with a noticeable mid-vein. The white flower clusters give it a somewhat attractive appearance late in the season, but this can be misleading given the damage the plant causes. In autumn, the leaves yellow and fall, but the root system remains active underground.

Does It Affect All Plants?

Japanese knotweed competes aggressively with other plants for light, nutrients and space. It can dominate an area, outcompeting native and ornamental species and leaving little opportunity for other vegetation to survive. While it does not produce chemicals to directly harm other plants, its dense growth and fast spread make it extremely disruptive. In heavily infested areas, it can completely smother borders, lawns and wild habitats, reducing biodiversity.

Is It Dangerous?

Japanese knotweed is not toxic to humans or animals, but it is considered dangerous in terms of the structural and environmental damage it can cause. Its roots can grow deep and wide, damaging foundations, drainage systems, roads and patios. It can also reduce property values and make it difficult to secure a mortgage if it is found near a building. Although it is not a direct health threat, its presence carries significant financial and legal consequences.

How Do You Remove It?

Removing Japanese knotweed is a slow process that requires careful planning. Digging it out may seem like the simplest solution, but unless every fragment of root is removed, it will likely regrow. Excavated material must also be handled with care, as it is considered controlled waste and must be disposed of at a licensed site. Root barriers and digging in combination with herbicide treatments can be effective, but full removal may take several seasons. Patience and ongoing monitoring are essential.

What Treatment Can I Use to Get Rid of Japanese Knotweed?

Systemic herbicides containing glyphosate are commonly used to treat knotweed. These are absorbed by the leaves and carried into the root system, where they gradually weaken and kill the plant. Treatment is most effective in late summer or early autumn when the plant is drawing nutrients into its roots. Multiple applications are usually required over several years. Any herbicide use should follow manufacturer guidelines and legal regulations, particularly if you are treating near water sources or wildlife habitats.

Is It Harmful to Pets?

Japanese knotweed itself is not poisonous to cats or dogs. However, caution is advised if you are using chemical treatments in areas where pets roam. Some herbicides can be harmful if ingested shortly after application. It is best to keep pets away from treated areas until the product has dried and the soil is safe again. Always check the safety guidelines on any product you choose to use and consult a vet if you suspect accidental exposure.

Can I Remove It Myself or Do I Need a Professional?

Small infestations may be tackled by a homeowner with the right guidance and persistence. However, larger or more established infestations often require professional intervention. Certified removal specialists have access to stronger herbicides and specialised equipment and are also able to provide legal documentation of treatment. This is particularly important for property sales, insurance or mortgage applications, where proof of management or eradication may be required.

How Does Japanese Knotweed Cause Problems?

The damage caused by knotweed stems from its vigorous root system, which can grow through walls, pavements and drainage systems. It creates pressure that can lift paving slabs, crack foundations and block pipes. It also disrupts garden design and planting plans, as it dominates space and returns even after heavy pruning or disturbance. In some cases, its presence can halt building projects or reduce the value of a property until full removal is guaranteed.

Japanese Knotweed and the Law

In the UK, Japanese knotweed is listed under Schedule 9 of the Wildlife and Countryside Act 1981, which makes it illegal to plant or encourage its growth in the wild. While it is not illegal to have it on your land, allowing it to spread to neighbouring properties or public land can result in legal consequences. Disposal of knotweed waste must follow strict environmental guidelines, and some councils may require a management plan if it is found during planning or development works.

Organic Methods of Removing Japanese Knotweed

For those wishing to avoid chemical herbicides, there are organic methods that may help weaken and eventually suppress Japanese knotweed. Repeated cutting or mowing of the plant reduces its ability to photosynthesise and weakens the roots over time. Smothering the plant with heavy tarpaulins or root barriers can also reduce growth by denying it light and moisture. These methods are less aggressive but often take longer and require consistent attention. While full eradication using organic methods alone is difficult, they can be effective as part of an integrated control strategy.