What is Japanese Knotweed: How to identify, Remove and Prevent

Japanese knotweed is one of the UK’s most invasive and problematic plants. It grows rapidly, spreads underground and can cause significant damage to your house. If left untreated, it can lower property values, affect mortgage applications, and even lead to legal disputes.

But how do you identify Japanese knotweed? What’s the most effective way to remove it? And how much does Japanese knotweed removal cost? This guide will help you understand the full impact of this plant.

Why is Japanese knotweed in the UK?

Victorians brought Japanese knotweed (Reynoutria japonica) to the UK in the 19th century. They used it as a garden plant, but it has become a very invasive species.

Despite its attractive appearance, this perennial plant quickly became a problem for the Victorians because it shoots up and is fast-growing with a very deep root system that can grow up to 3 metres deep with a radius of 7 metres wide. It can also grow up to 10 cm each day in summer.

It’s estimated that 1.45 million homes are affected by this plant in the UK.

What does Japanese knotweed look like?

At first, people loved its red shoots and heart-shaped green leaves. It was a popular choice for gardens in spring and summer. However, the Victorians soon discovered its destructive nature and turned against this once-favoured plant.

Most people do not know what the plant looks like. This makes it hard to identify.

Above ground, the plant looks fairly nondescript due to its unassuming appearance. Some mistaken plants that look like Japanese knotweed include bamboo and field bindweed. As a result, it can easily go undetected.

Tips to identify Japanese knotweed

• The stems are hollow, bamboo-like, and red-purple.
• Heart-shaped leaves or shield-shaped, bright green, growing in a zigzag pattern along the stem.
• The plant sometimes blooms with small white spiky flowers that appear in late summer.
• The roots are thick, red-stemmed and have an orange colour inside. The roots of this invasive weed are capable of growing new plants even from tiny fragments.

Why is Japanese knotweed a problem?

Japanese knotweed can cause serious issues for homeowners because its roots can grow down as much as 7 feet (2.1 meters).

As such, if left unchecked, the roots can exploit weaknesses in any building, causing significant structural damage to walls, drains, floors and hard surfaces. Also, because it can grow up to 10cm a day, it can create new areas of infestation.

This can result in costly repairs.

Under UK law, if you find Japanese Knotweed on your property, it is your legal responsibility to contain it. For example, it is illegal to let it spread to nearby land. If you do, you could face legal action under private nuisance laws.

Some homeowners have won lawsuits against neighbours or developers who let the knotweed spread onto their land. Compensated for removal costs and loss of property value.

What to do if you find Japanese knotweed

Firstly, if you’re unsure whether or not you have Japanese knotweed, a Japanese knotweed surveying service can confirm its presence. DIY removal rarely works.

If you find it growing in or near your property, and have it removed, you may be required to take out a special knotweed indemnity policy. This is to prevent potential future attacks on the plant and to mitigate against all damage it can do.

These special indemnity policies provide cover for the cost of treatment. Any damage caused by the plant, third-party legal fees (should the plant have spread onto neighbouring properties). And the resultant devaluation of any property found with Japanese knotweed growing in or near the grounds.

If you have any doubts about Japanese knotweed, speak to the Environmental Agency, or contact specialist removal companies.

How to get rid of Japanese knotweed

Summer and early autumn are the most common times for the plant to grow. However, it’s worth being aware of the potential threat it could pose all year round.

If you already have Japanese knotweed growing on or near your property, there are a few courses of action you can take – either chemical or non-chemical. Each has its advantages and disadvantages.

Japanese knotweed eradication can be expensive and can take up to three years to have any effect.

But here’s what to do if you find Japanese knotweed:

• Try to stop it spreading. Spraying or injecting the stems with approved herbicides (chemicals) can be an effective treatment to stop knotweeds spreading. You must do this every year until there is no evidence of regrowth. Another way to prevent it from spreading is to install root barriers, which can help contain the spread. However, do not cut, mow, or trim it as this can cause new growth!
• Removal: dig it out, let it dry, and burn it. This involves digging down to the roots and disposing of the plant appropriately. You can’t dispose of it with normal household waste, as that can cause it to spread. Never put it in green waste bins. Professional treatment is usually necessary to ensure complete eradication.
• Alternatively, some homeowners choose to use the eco-friendly MeshTech method.

It’s important to note that trying to tackle the problem yourself can make the situation worse or could affect guarantees you might require in the future. So, it’s important from the outset to get the correct advice with a coordinated approach with neighbouring landowners.

Where can the plant be found in the UK?

Japanese knotweed is widespread across the UK, particularly in:

• Bristol
• Merseyside
• London
• Greater Manchester
• Lancashire
• Birmingham

You can check a Japanese knotweed heat map to see if your area is affected.

What does it mean for those buying or selling a home with Japanese knotweed?

Whether you’re buying or selling, it’s something you need to take seriously. Here’s what it means, depending on which side of the property deal you’re on.

If you’re selling a home with Japanese knotweed

Sellers have a legal duty to disclose the presence of this invasive plant on the TA6 form, which is the property information form every seller fills out when listing a home. If you know there’s knotweed and fail to mention it, you could be held responsible down the line. It’s not something to ignore or hope will go unnoticed.

Before you even list your home, it’s worth checking if knotweed is present, especially if you’re unsure. Getting a professional in to confirm it or rule it out can save a lot of hassle later. If it is there, most sellers arrange for a professional removal company to assess the problem and put together a treatment plan. That plan should ideally include a guarantee, something that can be handed over to the new owner.

It’s often the case that mortgage lenders won’t approve a buyer’s application unless there’s proof that the knotweed is being dealt with. So, having everything in place before your home goes on the market. Including any documents relating to treatment or guarantees can help avoid delays or falling through altogether.

Bottom line? If you know about knotweed, be upfront. It could feel like a setback, but dealing with it early and transparently often makes the whole process smoother.

If you’re buying a home with Japanese knotweed

Before committing to buy a house with Japanese knotweed, be 100% sure of its impact on the property, because it can be tough (and costly) to remove.

If a house you’re looking to buy has Japanese knotweed, the seller must mention this on the TA6 form. Always double-check this document and ask your estate agent directly. While agents aren’t required to investigate, they do have to pass on anything they know. So, if they’ve been made aware of knotweed, they can’t keep that to themselves.

Mortgage lenders will usually ask for evidence that the knotweed will be professionally managed before they approve the loan. This is where a proper treatment plan comes in. One prepared by a specialist, not a quick DIY fix. The plan should ideally come with a guarantee that covers the new owner, too. Most of the time, the seller takes care of this before the sale goes through, but it’s important you see the documents for yourself and know what’s included.

So, if a seller discloses its presence, take a good, hard look at things before you commit. You might see it as an opportunity to negotiate the house price, but the reality is that the ongoing maintenance costs and hassle could far outweigh any savings you make on the property.

Research is absolutely key. Want to learn more about your area and what else to expect? With a property report, you can find out everything from local schools to what the neighbours are like.

Japanese Knotweed FAQs

Is Japanese knotweed poisonous to touch?

No, Japanese knotweed is not poisonous and won’t cause burns or rashes. However, it’s best to wear gloves when handling it, as the stems can be sharp.

Can Japanese knotweed grow back after removal?

Yes, if even a tiny piece of root remains, it can regrow. That’s why professional treatment is recommended.

How much does Japanese knotweed removal cost?

Removal cost for the plant can vary from small infestations, generally needing herbicide treatment costing between £1,500 to £5,000. Whereas large removals can cost upwards of £5,000.

Does the plant affect house prices?

Yes. A property with untreated Japanese knotweed can have an effect on the house price.

Last Updated: June 6th, 2025