Why Japanese knotweed can ruin your life

The large green leaves are attractive and the tall bamboo-like stems can add structure and definition to your garden.

Japanese Knotweed in a garden with a white greenhouse

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The knotweed rap sheet

  • Grievous structural harm  Guilty
  • Theft of £2,500  Guilty
  • Anti-social behavior Guilty
  • Squatting  Guilty
  • Provoking civil unrest  Guilty  

But don’t be seduced. Japanese knotweed - or fallopia japonica – which was introduced to the UK in 1825 as an ornamental plant, is now the scourge of thousands of properties across the UK.

It’s causes real strife and costs victims thousands of pounds.

So here’s what you need to do!

  1.  Find out if Japanese knotweed is growing in your garden
  2. Get rid of it. As soon as you can.
  3. Read on to find out more...

Plant identification

If you suspect you have a knotweed problem, it’s important to properly identify the plant before you panic.

The bamboo-like stems or canes have characteristic purple flecks and grow to about 7ft tall in the spring and summer.

The leaves are large at up to 14cm (5.5 inches) and shaped like a heart or spade. Creamy white ‘tassles’ appear in the late summer and early autumn, measuring up to 15 cm.

Growth and spread

The problem is the speed with which the plant grows and spreads – and the fact the roots can work through tarmac and brickwork and compromise your house’s foundations.

It dies back to ground level in the winter, but between April and September it can shoot up by as much as 20 centimetres a day – 20 centimetres a day – and reach over two metres high.

It doesn’t produce viable seeds in the UK, but it spreads through an underground root system, which can penetrate more than four metres deep and extend for seven metres.

Fragments and cut plants can also cause new growth. So it’s highly unlikely that you’ll eradicate it by chopping it back and yanking at the roots.

Indeed, you’ll probably need to pay a professional to do the job.

Structural damage

But it’s not just your garden you have to worry about. If Japanese knotweed takes root, it could affect your property.

It can, for example, grow through tarmac and cause structural damage to your property. The roots – properly known as rhizomes – can crack or block underground drains and disrupt patios, driveways and paving.

The plant can undermine walls and easily cause lightweight structures such as garden sheds to collapse.

Under control

It’s not illegal to have Japanese knotweed in your garden, but you can get into trouble if you don’t control the plant and it starts to spread beyond your property.

It is an offence to plant or cause Japanese knotweed to grow in the wild.

“But it’s not just your garden you have to worry about. If Japanese knotweed takes root, it could affect your property..."

Official action

The government is so concerned about knotweed that the Home Office has recently reformed the rules on anti-social behaviour, giving local councils and the police the power to issue a community protection notice to householders who don’t get their knotweed in hand.

That’s what’s commonly known as an ASBO. For having a plant in your garden that’s not even cannabis.

A community protection notice is pretty serious and can order someone to “control or prevent the growth of Japanese knotweed or other plants that are capable of causing serious problems to communities.”

A breach of the notice would constitute a criminal offence and could result in a fine of up to £2,500.

Neighbour disputes

Knotweed can also cause disputes between neighbours.

Who is responsible for the knotweed? Did it grow in your garden and spread to your neighbour’s property? Or did it originate on the other side of the fence?

If you cannot agree an action plan and division of costs, you could end up in the civil courts with a claim for damages. 

Cutting your loses

Japanese knotweed is strong and tenacious, so it’s not easy to bring under control.

Cutting the plant is often ineffective because it does nothing to tackle the underground rhizomes.

You should also never strim Japanese knotweed as it will then spread to surrounding areas.

Waste disposal

You could try digging it out of the garden. But its rhizomes run deep, so it’s hard work to eradicate the weed completely.

There’s also the problem of waste disposal. You can’t just chuck the stuff in the garden bin because knotweed is classed as ‘controlled waste’ under the Environmental Protection Act 1990.

It must therefore be taken to a licensed landfill site by a licensed waste carrier.

Alternatively, you can allow the weed to dry out and burn the debris.

Chemical warfare

Many gardeners prefer to treat their knotweed with a chemical spray – and a glyphosate-based weedkiller is the most effective. Look for a brand that specifically targets Japanese knotweed and follow the instructions carefully.

It usually takes two or three seasons to be rid of the plant completely, so be persistent and patient.

Call a specialist

It’s probably better to call in a specialist if you suspect that knotweed has infiltrated your garden.

The charges vary depending on the region and the height and spread of the weed, but could run into hundreds if not thousands of pounds.

Make sure you understand the fees before any treatment plan begins and check that the firm offers a guarantee or warranty.

In other words, if the plant comes back, they should come back too.

Insurance cover

Most buildings insurance policies do not cover the cost of any treatment or removal of Japanese knotweed.

You don’t have to disclose the presence of the plant on your buildings insurance proposal form unless asked to do so – at which point you need to be upfront and honest if the stuff is growing on your land.

If the plant has caused any structural damage to your property, such as subsidence, then you should be able to make in a successful claim, provided you have taken reasonable steps to eradicate it.

In other words, if you ignore the presence of the vicious vegetation, your claim for structural damage might be turned down on the basis that you did not exercise reasonable care to prevent the cause of the problem.

Property value

You won’t be surprised to learn that the presence of knotweed can have a detrimental effect on the value of your home.

It can also make it difficult to buy or sell because banks and building societies are often reluctant to offer mortgages on properties with knotweed problems. 

Mortgage trouble

RICS, the building surveyors’ association, suggests that knotweed is a potential risk if it is found within seven metres of your property.

But lenders adopt different attitudes to the risk. Some refuse any mortgage application if there is even the slightest evidence of knotweed, now or in the past.

Other banks and building societies will grant a mortgage as long as a treatment plan is in place, or the knotweed has been removed by an approved specialist.

Please note: any rates or deals mentioned in this article were available at the time of writing. Click on a highlighted product and apply direct.


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