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 answer these questions and more, helping you understand the full impact of this troublesome plant.

What is Japanese knotweed?

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 to the Victorians. Japanese knotweed shoots up and becomes fast growing with its deep root systems.

This Japanese knotweed plant can grow up to 10cm per day in peak summer, more generally up to 2 cm a day in early spring but appears to die in winter. The underground rhizomes (roots) can grow up to 3 metres deep with a radius of 7 metres wide. Making removal extremely difficult.

It is estimated that 1.45 million homes are affected by this weed in the UK.

But what can you do about it? We take a closer look at why it is often seen as a nuisance.

What does Japanese knotweed look like?

Initially admired for its red shoots and heart-shaped green leaves, it was a popular choice for herbaceous borders during spring and summer. However, the Victorians soon discovered its destructive nature and turned against this once-favored plant.

So, how to tell if you have Japanese knotweed? Many people are unsure of what the plant looks like, making identifying it difficult and some plants get mistaken for Japanese knotweed.

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

However, looks can be deceiving! Below ground is another matter altogether.

Japanese knotweed identification:

• 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 (rhizomes) 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 isn’t just a garden nuisance—it can cause serious issues for homeowners, sellers and buyers.

Its roots, which can extend down to 7ft render, are virtually impossible to remove yourself, without the use of extreme chemicals.

If left unchecked, these roots can exploit weaknesses in any building. Causing significant structural damage to walls, drains, floors and hard surfaces. This can result in costly repairs. It can also grow up to 10cm a day, easily creating new areas of infestation.

This means that this plant not only affects the health of your garden but your entire property also!

Under the Japanese knotweed UK law, it is not illegal to have Japanese knotweed on your property, but it is illegal to allow it to spread to neighbouring land. If this happens, you could face legal action under private nuisance laws.

Some homeowners have successfully sued neighbours or developers for allowing Japanese knotweed to spread onto their land, winning compensation for removal costs and property devaluation.

How to get rid of Japanese knotweed

It’s tough, but there are some methods you can try to remove it.

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 their 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 strim 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 without killing it first. 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.

If you’re unsure whether you have Japanese knotweed, a Japanese knotweed surveying service can confirm its presence.

Can you remove Japanese knotweed yourself?

In theory, yes—but in practice, DIY removal rarely works. The roots are so deep and extensive that most attempts fail. You must dispose of Japanese knotweed correctly, taking it to a licensed landfill or burning it on-site. Using a professional removal service ensures that it is completely eradicated, legal compliance and a certification for your mortgage lender.

What kills Japanese knotweed permanently?

The most effective solution is a combination of herbicide treatment and excavation. Simply cutting or digging up the plant won’t work unless every single root fragment is removed.

What to do if you find Japanese knotweed

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 of 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 doubt about Japanese knotweed, speak to the Environmental Agency, or contact specialist removal companies.

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.

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 between £5,000 up to £20,000+.

Does the plant affect house prices?

Yes. A property with untreated Japanese knotweed can have an effect on the house price, generally it could lose 5 to 15% of its value.

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

Sellers will need to disclose the presence of this invasive plant on the TA6 form.

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

If a house you’re looking to buy has Japanese knotweed, then this must be mentioned on the TA6 form from the seller.

Mortgage lenders often ask for proof that the plant will be dealt with before they approve the loan. A professional removal company usually needs to create a treatment plan with a guarantee that can be passed to the new owner. Most of the time, the seller arranges this before the sale goes through.

So, if a seller discloses its presence, take a good hard look at things before you commit.

While you may view it as an opportunity to negotiate a house price. The maintenance costs involved and the hassle of removing it might far outweigh any money you’d save on the property.

Research is absolutely key! Want to learn more about your area? With a property report, you can find out everything you need to know about a specific area, from local schools to who the neighbours are.ic area, from local schools to who the neighbours are. Get your full report here!

Last Updated: March 5th, 2025