Question 1

How deep are Japanese knotweed roots?

Accepted Answer

Japanese knotweed roots can develop a system that burrows up to 3 metres deep underground and a further 7 metres horizontally from where the plant breaks ground. The depth and complexity of this root system make it a difficult and costly task to remove completely. Whilst digging out the plant is considered to be one of the most effective methods of eradicating Japanese knotweed, the cost and disruption of doing so can be prohibitive to some.

Question 2

Does Japanese knotweed smell?

Accepted Answer

Japanese knotweed does not have a particularly distinctive smell. Its scent is not considered to be one of its defining features and does not contribute to its undesirable reputation.

Question 3

Is Japanese knotweed dangerous?

Accepted Answer

Japanese knotweed is not poisonous, nor does it pose any physical danger to animals or people. The plant does, however, pose a threat to native plants that are not as well equipped to compete with this foreign element. The environmental impact that this plant has on our own wildlife is often overlooked in favour of the financial costs of treating it. When the plant is allowed to thrive on public waterways or on disused industrial lots, it can quickly stifle the growth of any other plants growing nearby.

Question 4

What does Japanese knotweed do to a house?

Accepted Answer

Japanese knotweed does not necessarily ‘write off’ a house. How the plant affects the property will depend on the severity of the infestation and how close the plants are to the buildings. Although it’s possible to find evidence of Japanese knotweed literally breaking through into homes, this is rare and usually the result of a combination of poor building maintenance and a particularly aggressive infestation. Japanese knotweed’s predominant effect on a house is financial. In the average case of Japanese knotweed discoveries, the value of the property is diminished between 5-20%.

Question 5

Can Japanese knotweed grow through concrete?

Accepted Answer

There is some photographic evidence to prove that Japanese knotweed can grow through concrete, however, this has only been noted to happen in scenarios where the infestation is particularly bad and the construction work is particularly shoddy. In extreme cases, Japanese knotweed is also know to disrupt independent structures such as garden sheds, greenhouses, fences. The plant can also slowly break through shoddy brickwork, paving and tarmac.

Question 6

Can Japanese knotweed damage foundations?

Accepted Answer

It’s possible for Japanese knotweed to damage the foundations of a house, but this will only happen when infestations are long-established and there are already weaknesses in the building. In very rare cases, Japanese knotweed has been known to break its way through floorboards and skirting boards which can lead to a house being unsellable, as in the case of the Joneses in Broxbourne who were recommended to demolish their entire home. Their property’s value plummeted from £350,000 to £50,000 - a rare example but one which has had an impact on the industry at large.

Question 7

Can you sell a house with Japanese knotweed?

Accepted Answer

It is legal to sell a house with Japanese knotweed, however, the invasive plant’s reputation often makes it difficult to sell up when the time comes to it. If you’re attempting to sell a property with Japanese knotweed then you should state that the property has been affected on the TA6 property form. Similarly, if you’re aware that the land has been treated at some point, even if the knotweed has died off, you should still mention it. Failing to mention or lying about your property being affected by Japanese knotweed could lead to a misrepresentation claim being brought against you.

Question 8

Can you get a mortgage on a property with Japanese knotweed?

Accepted Answer

You can get a mortgage on a property with Japanese knotweed, but most mortgage lenders will first ask to see evidence of a knotweed management plan being in place. This plan will prove that you have hired a PCA-accredited removal firm to manage the removal of the plant, and will also be insurance backed, so that in the event that the firm goes out of business before the plan is complete, another company will carry on the work. Although some lenders have relaxed their stance on Japanese knotweed, there are some that still refuse to give mortgages for properties affected by it. Re-mortgaging properties that have recently become infested can also be difficult, depending on the lender that you’re dealing with.

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