What is Japanese Knotweed?

Japanese knotweed identification, first you need to identify the plant – so what is it? Japanese knotweed (Fallopia japonica) and its hybrids are a non-native, invasive species of plant. Since it was introduced into the UK as an ornamental garden plant in the mid-nineteenth century, it has spread across the UK, particularly along watercourses, transport routes and infested waste areas and of course private gardens.

Plants within their native range are usually controlled by a variety of natural pests and diseases. When plants such as this are introduced into new areas, that are free from these pests and diseases, they can become larger and more vigorous. They invade natural habitats and out-compete the native plants and animals that normally live there. Rivers, hedges, roadsides and railways form important corridors for native plants and animals to migrate, and large infestations of non-native weeds can block these routes for wildlife.

But how easy is Japanese knotweed identification?

What Does Japanese Knotweed Look Like?

What does Japanese knotweed look like?

Japanese knotweed is a rhizomatous (produces underground stems) perennial plant with distinctive branching, hollow, bamboo-like stems, covered in purple speckles, often reaching 2-3 m high. The leaves of the mature plant are up to 120 mm in length with a flattened base and pointed tip and are arranged on arching stems in a zig-zag pattern.

The plant flowers late in the season, August to October, with small creamy-white flowers. The rhizome system may extend to, and beyond, a depth of at least 2m and extend 7m laterally from a parent plant. During winter, the leaves die back to reveal orange/brown coloured woody stems which may stay erect for several years. Stem and leaf material decomposes slowly, leaving a deep layer of plant litter.

From March to April, the plant sends up new shoots, red/purple in colour with rolled back leaves. These shoots grow rapidly due to stored nutrients in the extensive rhizome system. Growth rates of up to 40 mm a day have been recorded. These features can help towards Japanese knotweed identification.

What Does Japanese Knotweed Look Like?

What does Japanese Knotweed look like through the seasons?


Japanese Knotweed does not enjoy the UK winter! After the first hard frost, the plant will loose its leaves and go into winter dormancy. The canes of Japanese Knotweed will continue to stand during winter but they will turn brown and become brittle.

Top Tip! – identifying Japanese knotweed is especially difficult in winter because of the lack of leaves and the canes looking ‘twig like’. You can also check the ground for fragments of old canes and also the crown of the plant for signs of growth areas!


Japanese Knotweed will start to grow as early as March in some places in the UK so it is important to be vigilant at all times of year! The growths will initially grow with triangular leaves and red stems. Sometimes they can look a little like asparagus!

Once the growths become more mature the leaves will ‘fill out’ and become less triangular and more ‘shield shape’ with a very flat base, smooth edges and a small tip. They will also lose their red colour and become a vibrant green, making Japanese knotweed identification much easier.

Early Summer

During summer, we have seen Japanese Knotweed grow upto 1 foot a week! The main canes of growth are primarily green with small red/purple specks on them. The stems that come off the main cane grow in a left/right zig/zag pattern. When identifying Japanese knotweed, remember the leaves are shield shape with a flat base, smooth edge and slight tip to the end of the leaf.

Late Summer

As the summer progresses and your Japanese Knotweed continues to grow taller and taller, it will get to a point where it stops growing in height and starts to flower in long creamy clusters. The flowering is designed for seed creation and dispersal but thankfully the seeds are not viable in the UK!

If you are worried about a plant and think it may be Japanese Knotweed, send it to us for a free quick identification from one of our specialists!

Why Is Japanese Knotweed A Problem?

Why is Japanese Knotweed such a problem?

Japanese Knotweed is a fast growing, invasive plant and can cause problems in both Urban and Rural areas. The plant damages the urban environment such as gardens and road verges, by pushing up through tarmac and paving, out-competing other species in the area causing both aesthetic problems, such as ruining garden landscapes and also structural problems, such as when the plant grows into walls and cracks, pushing them apart. This is why Japanese knotweed identification is so important.

As well as rendering a property as ‘unmortgageable’ by the majority of the UK major lenders, the following are areas of residential property that can be adversely affected by the presence of Japanese Knotweed. Although these are the worst case scenarios it is worth considering when dealing with this invasive weed.

Drains and other buried services

Knotweed rhizomes can exploit existing cracks and gaps in the pipes in their search for water, which will further damage and, in some cases, block the drains. Large, densely packed clumps or ‘stands’ of Japanese Knotweed can disrupt drain runs. In the worst cases, the drains must be rebuilt.

Patios, paths and drives

Japanese Knotweed can grow between slabs and movement joints of concrete drives and disrupt brick paving. Repairs can involve the removal of the existing paving and bedding material, treatment of the plant, removal of the disruptive crowns and roots and replacement of the path, patio or drive.

Boundary and retaining walls

Closely packed growth can push its way under garden walls with shallow foundations. The mass of the stands can ‘push over’ retaining walls, often resulting in sudden collapse.


Vigorous stands of Japanese Knotweed can overwhelm lightweight, insubstantial and poorly founded outbuildings such as garden sheds, greenhouses and in some cases, poorly built garages.


Although the effects will be similar to those described for outbuildings, owners, valuers and surveyors usually attribute greater importance to these structures.


The invasive nature of the plant can ruin well-planned and well-stocked gardens. Some owners spend tens of thousands of pounds on renovating and redesigning outside spaces, including sophisticated water features and bespoke outbuildings.

The plant can be very easily spread and in the UK the plant is mainly spread through rhizome fragments or cut stems. Greenhouse trials have shown that as little as 0.7 gram (finger nail) of rhizome material can produce a new plant within 10 days. Cut fresh stems have also been shown to produce shoots and roots from nodes when buried in soil or immersed in water. Once cut stem material has been allowed to dry out thoroughly and has reached the orange/brown ‘woody’ stage, there is no further regeneration. Rhizome material may take much longer to die and may remain dormant for long periods, possibly as long as 20 years.

The spread of Japanese knotweed is a serious threat to our countryside, and the native plants and animals that rely upon it. Tackling the plant should be taken very seriously with thorough planning and execution if we are to combat this invasive weed. If you are unsure whether you have been successful in identifying Japanese knotweed, get in touch with CYB Environmental.

Japanese Knotweed RICS

RICS – Management Category Assessment

A property is considered as being affected by Japanese Knotweed if it is found within the boundaries of a property or within 3 metres outside of the property boundary. To help understand the correct level of control, the Royal Institution of Chartered Surveyors (RICS) have created a framework, based on the management of Japanese Knotweed. This framework is the Japanese Knotweed Management Category assessment, categorised from A – D , with an approach on the management of Japanese Knotweed. The framework focuses on the damage that Japanese Knotweed may have caused, and the impact to loss of amenity space.

Control and Removal methods

Japanese Knotweed Chemical Treatments

Chemical control

Chemical control is the application of specialised herbicides, after identifying Japanese knotweed, over a period of several growing seasons. This is often the most economical treatment option and will cause the least amount of disruption. Especially so in a residential context, where space is limited and property boundaries are closely located. Planned and managed chemical control is often the only realistic option for most properties in terms of practicality, cost and the need to satisfy lender requirements. Once the plant is dead, it is possible to cut and burn them. Ideally, burnt material should not be removed from the site as the risk of contamination is increased.

Japanese Knotweed Removal

Excavation of the plant and its roots

After identifying Japanese knotweed, the plant can be cut and the infested soils can be excavated and removed to an off-site, appropriately licensed, waste-management facility. The volume of excavated soil can vary from site to site and is an expensive and time consuming type of removal.

Japanese Knotweed Management

On-site burial and/or
encapsulation with membranes roots

Japanese Knotweed can be excavated and then buried on-site, but it must be covered with a specialist root barrier membrane to prevent any re-growth. A root barrier membrane can also be used to encapsulate Japanese Knotweed where space does not allow burial.

Our experts will be happy to discuss the best removal method to your specific requirements.

Contact Us


London: 020 3005 8755
Bristol: 0117 428 0177
Cardiff: 0292 167 1147
3 Borthwick Street, London SE8 3GH