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Japanese Knotweed and Mortgages - What You Need to Know

Posted 27 November 2017 by Nick Parkhouse

Japanese knotweed can make getting a mortgage tough. Here’s everything you should know about it...

It may be pretty, with lovely white flowers, but Japanese knotweed is one of the biggest problems facing British homeowners today.

The Environment Agency describe Japanese knotweed as “indisputably the UK’s most aggressive, destructive and invasive plant”.

So, what do you do if you have a Japanese knotweed problem? What are lenders’ attitudes to the plant? And how does Japanese knotweed affect your mortgage? Our guide explains everything you need to know.

What is Japanese knotweed and how does it damage property?

Japanese knotweed is a strong-growing perennial with tall, dense stems. It arrived from Japan in 1825 as an ornamental plant and it spreads through deeply-penetrating underground stems, called rhizomes.

The problem with Japanese knotweed is that it is an invasive plant that can cause serious trouble to any property. The plant's roots can extend up to 3m in depth and 7m in all directions and it can grow at a rate of more than a yard a week.

The roots can penetrate deep into the ground, damaging your property’s foundations, walls or drainage systems.

How is Japanese knotweed detected?

During spring, you can spot Japanese knotweed by looking for reddish/purple shoots that appear from the ground and fat, asparagus-like ‘spears’. These shoots can grow up to 2cm a day, quickly forming dense clusters of bamboo-like stems that develop green shovel-shaped leaves.

By early summer the mature Japanese knotweed stems are hollow, with purple speckles. The plants can reach 3m in height and the leaves alternate on each side of the stem producing a zigzag pattern.

The flowers that emerge by late summer are creamy-white in colour, and appear in lengthy cluster/spike formations.

Who is responsible for the prevention and eradication of Japanese knotweed?

It is not illegal to grow Japanese knotweed, but you must keep it under tight control and prevent it from spreading into the wild or to neighbouring gardens.

If Japanese knotweed is on your land, then it is your responsibility to deal with it. You do not have to remove the plants or control them on your land – although this is recommended – but you could be prosecuted if you let knotweed spread.

You could be fined up to £5,000 or be sent to prison for up to two years if you let plant material spread into the wild or into a neighbouring garden.

What are the implications of getting a mortgage on a property affected by Japanese knotweed?

The presence of Japanese knotweed can have an effect on the value of a property and a property’s mortgageability.

The seller has an obligation to disclose the presence of knotweed during pre-contract enquiries, while the estate agent also has an obligation under consumer protection regulations to advise you of any material facts that would affect your decision to buy. The guidance to these regulations identifies Japanese knotweed as being ‘material’.

Failure to disclose these details can result in legal disputes between buyers and sellers.

If you are considering buying a property where Japanese knotwood is identified, or if the lender's valuation report unexpectedly identifies the presence of knotweed, you will need to consider carefully how to eradicate it, how much this will cost, and who will bear the cost.

Until the knotweed is eradicated, and the property certified clear of the weed, there may be an effect on the lender's willingness to lend.

Mortgage lenders will generally need evidence of treatment that will eradicate the plant as a condition of lending.

How can I get a mortgage if Japanese knotweed is being detected?

Surveyors who inspect property for mortgage purposes are instructed to report to lenders where knotweed is present.

Each lender has a different policy on Japanese knotweed and mortgages. Lenders will often consider a mortgage if knotweed is present depending on its severity, proximity to the property, and other factors.

For example, Santander will lend if a professional has carried out remedial work, although they may insist you keep ongoing costs of control in a separate savings account. Leeds Building Society will not lend if the surveyor considers that Japanese knotweed is likely to affect value or saleability in the future, while Nationwide also requires an insured professional to eradicate the problem before they will lend.

What are the costs of getting rid of Japanese knotweed?

Getting a professional in for Japanese knotweed eradication may be a condition of your mortgage. Read our interview with the managing director of one of the UK’s biggest knotweed control firms to find out more.

However, you can also deal with the problem yourself. Guy Barter, chief horticultural adviser at the Royal Horticultural Society (RHS), says: “We are not talking about plants from another planet such as triffids. You can often treat knotweed yourself.”

There are three main ways to treat the problem:

  • Spray with chemicals – you can use approved pesticides to tackle the problem, although it may take three years before the underground rhizomes become dormant. You may need to get permission from Natural England if the area is protected, for example sites of special scientific interest, or from the Environment Agency if the plants are near water.
  • Bury plants – you can bury Japanese knotweed at the site where it’s produced as long as you bury it at a depth of at least 5m, cover the plant remains with a material that does not allow the plant to grow through it. Make sure that you do not bury any other types of waste with it.
  • Burn plants – you can burn the plants, although knotweed crown and rhizome may survive burning.

Bear in mind that Japanese knotweed is classed as ‘controlled waste’ under the Environmental Protection Act 1990 and so it must be disposed of at a licensed landfill site.

My neighbours are affected by Japanese knotweed. What should I do?

You should firstly contact the property/land owner or occupier and ask them to prevent any weeds spreading onto your land that are controlled by law.

If you’re concerned that a Japanese knotwood issue is not being controlled, you can send an ‘injurious weeds complaint form’ to Natural England. There have been legal disputes between neighbours where one party believes the other is not dealing with a knotweed problem.

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