Please Note: This Article is 9 years old. This increases the likelihood that some or all of it's content is now outdated.

For Landlords, the discovery of Japanese knotweed can be a real headache. Onward sales will be hampered until the problem is resolved, disagreements among tenant communities may make resolution tricky and, of course, there’s the issue of cost and where the financial and legal liabilities lie.

Alison Boothby untangles this knotty problem…

Japanese knotweed was introduced into the UK from Japan in the 1840s as an ornamental plant and is now the number one on the list of the UK’s most invasive plant species. The Environment Agency has described Japanese Knotweed as “indisputably the UK’s most aggressive, destructive and invasive plant”. It is particularly rampant along waterways, railways and on many brownfield sites and its rapid growth – up to three metres in height – means that it overshadows native plant species, has a significant impact on wildlife and causes damage to property. It has been estimated that it would cost in excess of £1.5bn to eradicate Japanese knotweed from the UK.

How to spot it

Japanese knotweed looks different at different times of the year and learning how to spot it is important. In the early spring red/purple shoots appear from the ground and grow rapidly forming canes. As the canes grow the spade shaped leaves gradually unfurl and turn green. The plants are fully grown by early summer and mature canes are hollow with a distinctive purple speckle and form dense stands up to 3 metres high. The plant flowers in late summer and these consist of clusters of spiky stems covered in tiny creamy-white flowers. During the late autumn/winter the leaves fall and the canes die and turn brown. The canes remain standing throughout the winter. The rhizome is the underground part of the plant. It is knotty with a leathery dark brown bark and when fresh snaps like a carrot. Under the bark it is orange or yellow.

How it spreads

All plants in the UK are female, so the seeds in the flower are not pollinated. The plant spreads by vegetative means with canes arising from the rhizome which grows underground, from an existing crown, where previous growth has taken place, or from a cut stem. All new outbreaks of knotweed result from fragments of viable rhizome that may be spread within soils being moved from site to site, by fly-tipping, or by natural processes such as river bank erosion, or by animal movement.
There are hybrid varieties of Japanese knotweed, notably Giant knotweed, which has larger leaves and generally taller plants. It is not as invasive as Japanese knotweed, but has the same legal status and treatment methods.


There are all sorts of myths about Japanese knotweed growing through hard surfaces. We asked Mark Thompson of Environet UK to explain: “It’s not entirely true to say that Japanese knotweed will grow through a hard surface, but in its insatiable quest for light and water, it will exploit any weaknesses in the formation and break through cracks in mortar, expansion joints in concrete, splits in drains and joins in paving. The most common form of property damage from Japanese knotweed is caused by laying a hard surface such as asphalt, concrete, patio slabs, driveway block paving and the like over Japanese knotweed infested ground.”

Underground sewers, drains and land-drains are particularly susceptible to Japanese knotweed. The knotweed rhizome will find its way into the smallest hole on a pipe joint to find water. The rhizome will continue to grow gradually blocking the drain and finally breaking it apart.

Mark again: “We have evidence of Japanese knotweed being spread down surface water drains. Pieces of rhizome break off the parent plant and are conveyed down the pipe, infesting the watercourse with Japanese knotweed at the point of discharge. Japanese knotweed can also grow within cavity walls. We have experienced stems and healthy leaves growing out of vents and air bricks located 2m above ground level. When knotweed grows in cavity walls it has the capacity to force the two skins of the wall apart. We also have a recorded incident of knotweed growing within a cavity wall of a single storey building, and forcing its way through the flat roof of the building.”

In practical terms, what happens is that driveways and pavements become uneven, potentially dangerous, as well as unsightly; pathways lift, walls collapse, drains need replacing, fences are pushed out of line or fall over – all of which are headaches landlords to deal with. But unless the underlying cause is dealt with – i.e the Japanese knotweed eradicated or correctly controlled – any work done to repair or to rebuild will all be wasted and the Japanese knotweed will return.

Awareness gap

We spoke to several landlords who told us that they often rely on tenants or on teams of groundsmen and maintenance staff to be their eyes and ears on the ground. The biggest problem seems to be a lack of awareness and understanding of Japanese knotweed. With the latest updates from the Law Society to the Property Information Form TA6 and the new CPRs (Consumer Protection Regulations) both specifically asking about the presence of Japanese knotweed, there’s certainly a question mark over whether just not knowing, or not having noted its presence will satisfy the liability under any Duty of Care obligations.” One thing is certain: landlords need to make sure that they, their tenants and all their contractors know what to look out for, can recognise it and take appropriate action.”

Legal implications

Alongside the practical frustrations of discovering Japanese knotweed on a property, there are legal implications too. In some cases you can be forced to clear infested land under the Town & Country Planning Act section 215 for Local Authorities. Environet UK is frequently approached by concerned property owners who have the plant encroaching from a neighbour which, if not handled carefully, may result in neighbour disputes and a claim under the common law of nuisance.

If you cause the knotweed to be spread off site, you could find yourself at the wrong end of criminal proceedings under either the Wildlife and Countryside Act 1981, or the Environmental Protection Act 1990 “duty of care”. Offences under these Acts can result in custodial sentences.

Soil contaminated with Japanese knotweed is classed as ‘controlled waste’ and must be disposed of at an appropriate licensed landfill site. If you consign knotweed infested soils off site other than strictly in accordance with these legislative requirements, whether intentionally or not, you will run the risk of prosecution.

Financial implications

The discovery of Japanese knotweed can be an expensive find, but the sooner it is dealt with correctly, the better. Left alone it will only thrive, cause more trouble and be more expensive to remove. It tends to be the sale of property that prompts action to destroy or control the plant as it’s virtually impossible to get a mortgage on a property with Japanese knotweed present. It makes sense now for landlords to make contingencies to deal with the problem upon discovery and not wait for it to delay or potentially stall a property sale. Leaving the problem will only make it more costly to remediate.

Treatment options

Your first consideration is to decide whether you wish to completely destroy the plant (eradication) or prevent further spread or damage (control). A Japanese knotweed specialist will be able to put forward the available options and advise the best course of action. In simple terms there are two courses of action: herbicide treatment or physical removal. Herbicide treatments are usually the most economical, but patience is required as they will take at least one growing season. Physical removal is swifter, but not possible in all situations. The good news is that whatever your situation, there is a solution.

For more information visit or call Mark Thompson on 01932 807837.

Please Note: This Article is 9 years old. This increases the likelihood that some or all of it's content is now outdated.



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