Should I buy a house with Japanese knotweed?

4 minute read

Japanese knotweed leaves

While you may think that Japanese knotweed is just another plant, in reality it can be extremely damaging to your home. If this plant is found nearby, you might not be able to claim on your home insurance to cover the cost of removing it. If you are considering buying a house with this invasive pest growing nearby, here is some important information to consider

What is Japanese knotweed?

Japanese knotweed has heart or spade-shaped leaves that grow in a zig-zag pattern along the stem. The stems that these leaves grow on are thick and look like bamboo canes. These individual canes can reach around seven feet tall. Japanese knotweed roots spread deep underground and grow through even the hardest of man-made materials, such as concrete. These roots find cracks in house foundations or paving and can make the issue much worse.

Since 2013, all house sellers that have Japanese knotweed growing on their property must declare this in their TA6 form. This form documents and details all information found during the conveyancing process.


What does Japanese knotweed do to a house?

This aggressive plant has been known to cause severe structural damage to homes. Its roots can push through walls and drains, up through paving or asphalt, and can make the foundations of your home weak and unstable. It’s even been known to grow up through people’s conservatories, coming through both the brick and the flooring. It can kill any other plants that are growing within its vicinity and is extremely difficult to get rid of.


Buying a house with Japanese knotweed present

If you’re planning on buying a house with Japanese knotweed, you should consider how much it will cost to eradicate it. According to the Non-Native Species Secretariat (NNSS), it can cost around £1,000 per square meter to have the plant removed and disposed of in a controlled manner so that it cannot spread elsewhere. Because of this, the value of the house is usually affected, and the property should be devalued accordingly.

The plant spreads so easily because of its stems. Otherwise known as rhizomes, this underground system can sprout new plants very quickly and effectively. Trials have shown that a stem that’s 10mm long can produce a whole new shrub in just 10 days. When the plant is trimmed, these rhizomes can produce more shoots, making it spread faster. If it originates from your property and has spread to your neighbours, it’s your legal responsibility to have it removed.

Japanese Knotweed

How to check for Japanese knotweed

During February to March, the Japanese knotweed will be developing new buds. When these first appear, they’re red in colour. As they develop into shoots, the redness will turn a lighter colour. These shoots grow into hollow canes that resemble bamboo. They’re green in colour with purple flecks. In Spring, approximately March to May, the leaves will be brown or yellow in colour. They will eventually turn a dark green in summer. In Autumn, Japanese knotweed will produce lots of small white flowers. Depending on what time of year you are visiting the house, you can use the descriptions above to check your garden for the plant.

Be careful when you’re visiting a property during winter, as Japanese knotweed can die away, so it may not be as noticeable.

Alternatively, you could use Environet’s heat map to determine the areas of the UK where Japanese knotweed is worst. You can also see how many cases of it have been found in your local area.


Does house insurance cover Japanese knotweed?

If you’ve had Japanese knotweed for a while and it has caused subsidence previously, your cover may be declined. It’s possible that your insurance company may want to know more, such as:

  • How long Japanese knotweed has been present
  • Whether it is on your land or your neighbours’
  • How far it is from the house
  • Whether it has caused any damage to your home

When it comes to fixing the problem, most insurance companies won’t pay the cost of having Japanese knotweed removed. This can cost tens of thousands of pounds. They may, however, compensate you for any damage that has been caused by the shrub, such as subsidence or damage to the building.

You do not legally have to remove Japanese knotweed from your land unless it’s causing a nuisance, but you can be prosecuted for causing it to spread into the wild. For example, if you try to dispose of the plant by leaving it on the side of the road. It is the homeowner’s legal responsibility to prevent Japanese knotweed from spreading and you could be sued if you don’t do so in the correct manner. It’s usually best to call in the professionals to remove it properly.


For more expert home advice, try exploring the rest of Age Co's Useful Articles.