Japanese knotweed damage is a serious threat to UK properties. This invasive plant can cause significant structural damage and reduce property values by up to 20%* – figures that should worry any property owner. *See this survey by RICS.
It’s growth pattern can be devastating to structures and other plants. It can grow through concrete, compromise the foundations of buildings, damaging them over time. And it can get out of control so fast if left untreated.
Japanese Knotweed damage can cause real financial risks. Beyond the initial repair costs there’s the long term impact on property value and marketability. Many mortgage lenders now require Japanese knotweed surveys before they’ll lend.
Understanding the risks that Japanese Knotweed growing on your land poses is key for anyone with property interests. The earlier you identify Japanese Knotweed and begin to treat Japanese Knotweed, the quicker you will prevent damage.
Is Japanese Knotweed Harmful to Humans?
Japanese knotweed is not harmful to humans and it’s not toxic but you should still take basic precautions:
- Is Japanese knotweed safe to touch? Yes it’s safe to touch, but wear gloves to avoid minor cuts from stems especially if you have skin conditions that makes you more sensitive to irritation from the stem.
- Is it dangerous to touch Japanese knotweed? No, no toxic effects from skin contact.
Although safe to handle, there’s many reasons why you shouldn’t cut Japanese knotweed. Cutting it can actually spread the problem (affecting other plants), even tiny rhizome fragments can grow into a new Japanese Knotweed infestation.
What is Japanese Knotweed and Why is it Such a Problem?
Japanese knotweed is a problem because :
- It’s non native invasive plant, so there’s no natural predators to control it
- Outcompetes native plants for resources
- Can grow through concrete, tarmac and building foundations
- Spreads rapidly through underground rhizomes up to 7 metres horizontally
- Rhizomes can remain in the soil for many years even when the visible growth appears dead
The rhizome system and aggressive growth habits cause property damage and environmental disruption.
The plant’s bamboo-like stems can grow up to 2-3 metres tall, with heart-shaped green leaves and small white flowers in late summer.
Plant growth and spreading often occurs when the rhizomes are fragmented during removal attempts, which can speed up the plant’s invasion into new areas. Hence why DIY removal is not advised.
Can Japanese Knotweed Damage a House?
In extreme cases Japanese knotweed can cause serious structural damage to buildings and even the house itself, but total destruction is rare.
Japanese knotweed infestations can be very damaging if left untreated. This can mean expensive repairs and devaluation of your property.
The extent of Japanese Knotweed damage depends on several factors:
How Japanese Knotweed Causes Structural Damage
Structural damage caused by Japanese knotweed occurs in several ways:
- Foundations: Rhizomes exploit existing cracks and weaknesses in foundations
- Pressure Damage: Above ground growth puts pressure on walls, fences and buildings
- Underground Infrastructure: Roots penetrate drainage systems and water pipes
- Concrete Penetration: In worst case scenarios knotweed can grow through poorly constructed concrete
Types of Property Damage
Common knotweed damage includes:
- Building foundations – weakening and cracking of structural elements
- Walls – accumulating pressure causes damage of mortar joints, garden walls and cavity walls, especially those with shallow foundations
- Drainage systems – rhizomes blocking pipes and causing water damage
- Hard surfaces – growth through paving, tarmac and concrete
- Garden structures – damage to sheds, greenhouses and fences due to vigorous growth
Seven Metre Rule for Japanese Knotweed
What is the Seven metre rule for Japanese knotweed? This rule comes from Environment Agency guidance which states that rhizomes can spread up to seven metres from visible growth. However the revised RICS guidance says Japanese knotweed is a threat if found within 3 metres of a property. The 7 metre rule affects:
- Property valuations and mortgage applications
- Insurance backed guarantees for removal work
- Risk assessments for neighbouring properties, including assessing the area that may be affected by rhizome spread
- Treatment planning and site investigation requirements
Your Legal Obligations
Its extensive rhizome system is capable of destabilizing and damaging property foundations, disrupting piping and water supplies, and compromising fences, boundaries, outbuildings, and even flood defences.
Is it illegal to have Japanese knotweed in your garden? Having knotweed isn’t against the law, but home owners do have responsibilities. You must declare it on the TA6 form when selling your property – this isn’t optional.
A low cost Japanese Knotweed survey helps you stay on the right side of the law. Hide knotweed from buyers and you’re asking for trouble. Court cases and hefty compensation payments can follow, like in the 2023 Downing v Henderson case where the defendant ended up paying £200,000 for not being honest about knotweed on their property.
What the Law Says
- The Wildlife and Countryside Act 1981 makes planting or causing Japanese knotweed to grow in the wild illegal.
- Under the Environmental Protection Act 1990, any soil contaminated with knotweed gets classified as controlled waste.
- The Anti-Social Behaviour Act 2003 gives councils power to issue Community Protection Notices if you don’t control knotweed properly.
- Our Japanese Knotweed and the Law page covers all this in much more detail.
Landowner Responsibilities Summarised
You must:
- Prevent spread to neighbouring properties
- Disclose presence during property transactions
- Dispose of contaminated material using licensed waste carriers
- Take reasonable steps to control infestations
Should Japanese knotweed be removed? Yes, prompt professional removal is essential to prevent further damage and comply with legal obligations.
Property Investment Considerations
Is it Worth Buying a Property with Japanese Knotweed?
Properties with Japanese knotweed can still be viable investments if:
- Professional treatment plans are in place with insurance backed guarantees
- Purchase price reflects remediation costs
- Mortgage lenders accept the management strategy
- Treatment is carried out by accredited specialists
Impact on Property Sales
Can I sell my house if my neighbour has Japanese knotweed? Yes, but you must disclose to potential buyers. Properties with a Japanese knotweed infestation can create a stigma and affect their saleability. The impact on your property value will depend on the proximity of neighbours and severity of the infestation.
Environmental Impact of Invasive Species
The environmental damage from knotweed goes way beyond individual properties and affects whole ecosystems.
Ecosystem Disruption
Japanese Knotweed growing on your land causes problems for local plant growth. Dense stands block out sunlight to other plants, effectively starving them of light and nutrients they need for plant growth. This sets off a domino effect – less native wildlife means less diverse habitats for insects, birds and small mammals that depend on them.
The plant also changes the soil over time. As it forms dense colonies it alters the soil composition and pH levels.
Impact on Waterways
Near rivers and streams Japanese knotweed plant growth is a big problem. The extensive root system can weaken riverbank stability which increases the risk of flooding for nearby communities. Dense growth along watercourses can also block natural drainage patterns.
Water quality suffers too. When knotweed dominates riverbank vegetation it reduces the diversity of plant life that normally maintains healthy aquatic ecosystems.
Professional Treatment and Control Methods
Japanese knotweed doesn’t give up easily. That’s why property owners usually need experts to handle identification, treatment and management properly. DIY attempts usually backfire.
Success comes from combining different methods:
Herbicide Treatment
Specialists use glyphosate applications for herbicide treatment and this is completed over several seasons. The timing of application matters – treat the plant at the right time and results are much better.
Excavation
Digging out all contaminated soil, removing everything (to a licensed landfill site), including root pieces that can regrow. Works well for commercial environments where time is of the essence.
Root Barrier
Physical barriers stop the plant reaching sensitive areas like foundations or neighbouring land. These containment systems work well.
Monitoring
Regular checks ensure any new growth is spotted quickly. Even after successful treatment, vigilance is still required because missed bits can start again.
Catching It Early
Finding Japanese knotweed quickly changes everything. Identify an infestation early and treatment becomes much easier and cheaper. Act fast and you stop the plant building those massive root networks that make removal such a nightmare later on.
Identification
- Bamboo-like stems with nodes
- Heart-shaped green leaves arranged alternately on stems
- Rapid growth in spring and summer
- Clusters of small white flowers in summer
- Red-purple shoots in spring
Read our How to Identify Japanese Knotweed Guide for more info.
Risk
Properties at risk are:
- Near waterways or railways
- With adjacent infestations
- On previously developed land
- In areas with known knotweed presence
Prevention
- Regular garden checks, especially near boundaries
- Proper disposal of garden waste to prevent spread
- Professional advice if you see suspicious growth
- Monitor neighbouring properties for infestations
Cost and Financial Planning
Japanese knotweed treatment costs vary depending on:
- Size and maturity of infestation
- Proximity to buildings and infrastructure
- Treatment method chosen
- Site access
- Long term monitoring
Early intervention typically costs £1,500-£8,000, whilst severe infestations may require £10,000-£50,000+ for comprehensive treatment. Read our Japanese Knotweed Removal Costs page for more detailed information.
Working with Knotweed Services
Professional expertise is key when dealing with Japanese knotweed. Here’s why you should use our services:
- Property Care Association (PCA) accreditation and an approved contractor
- Industry qualifications
- Insurance backed guarantees for long term protection
- Full site surveys and management plans
- Compliance with waste regulations and the Environment Agency
- Local authority liaison if required
Japanese knotweed is a serious but manageable threat to UK properties. Knowing the risks, legal requirements and Japanese Knotweed treatment options mean landlords can make informed decisions about this non native invasive species.
Professional assessment and treatment planning is the foundation for protecting property values and structural integrity whilst being fully compliant with UK regulations for this non native invasive species.
