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What is Japanese Knotweed and how could it affect your house purchase?

Harriet Meyer / 10 June 2015

With its red stems and green leaves, you might think Japanese Knotweed is merely a harmless, and even pretty plant. Yet it's causing misery for many going through the property buying and selling process.

Japanese Knotweed
Japanese Knotweed's roots can cause damage to house foundations

What is Japanese Knotweed?

Also known as Fallopia Japonica, this plant comes to life in spring after lying dormant in the winter months. It originally arrived in Britain in 1825 as an ornamental plant brought over by a botanist who found it growing on the sides of volcanoes. It rapidly spread through watercourses and the movement of soil in construction.

It can also grow wildly high at up to 7ft tall, putting an end to the life of all other plants around it. The plant has a lime-green long, thin, hollow stem that appears similar to bamboo, with heart-shaped leaves. It’s shoot are flecked with red and purple marks.

In the summer it'll produce cream flowers before dying back in September and November, causing stems to turn brown.

What is the problem?

In Japan, the volcanic climate kept this plant’s growth at bay. However, in Britain, it’s got the conditions to grow unabated.

Mortgage lenders know this and often refuse to give mortgages because of the plant's destructive tendencies. Its roots can bury deep into the ground, risking damage to a home's foundations and any thing around this such as drainage systems.

It’s not illegal to grow knotweed in your garden, although it is illegal to do so in the wild. However, if you grow it at home it’s meant to be kept under control to prevent it from spreading - which can be almost impossible. At worst, the council can insist that you pay to get it removed, which can cost thousands of pounds.

At best, it can wipe thousands of pounds off property values. At worst, it may stop the sale in its tracks if a mortgage lender refuses to offer a mortgage. So there are few, if any, homeowners who would grow it voluntarily.

Read more about things that affect your application for a mortgage.

What can you do?

Take pictures and email these to a weed control company. You need to find out if your suspicions are correct and it really is the dreaded knotweed. A specialist will typically charge around £175 to visit the site and survey the situation.

It's possible you may be able to remove the plant yourself but this can be tricky as you have to get rid of every trace of the root, and it must be disposed of at licensed landfill sites. It’s also possible to gradually kill it with chemicals, although this takes time you might not have.

Alternatively, you can pay an expert to destroy it.

Read more about selling a problematic property. 

Saga Home Insurance provides cover that goes beyond what you might expect. For more information and to get a quote click here.


The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.