Damage caused by Japanese Knotweed

Japanese Knotweed Damage

Japanese knotweed is a non-native invasive plant that can cause problems to your property.

Is Japanese Knotweed Dangerous?

If Japanese knotweed grows close to a property building, retaining/garden wall, fence or garden building, the underground roots and rhizomes can damage these structures as they exploit the cracks/mortar joints and weaknesses. The pressure exerted by the expanding rhizomes will result in damage. It will push up through tarmac car parks and drives and paved areas.

In their search for moisture, Japanese knotweed roots and rhizomes can interfere with drainage pipes and other structures, blocking and sometimes lifting pipework and clogging sumps and drainage pits. Other underground infrastructures are at risk, such as cabling and water pipes. Typical damage from Japanese knotweed is shown below.

Can Japanese Knotweed Cause Damage to Property?

Japanese knotweed will exploit existing weaknesses in property underground services, walls, foundations, fences, out-buildings and conservatories. In its search for moisture, the rhizomes will forge their way through structures without regard for their purpose. Whilst the rhizomes can create problems underground, the aerial growth provides very dense cover over a wide area, preventing native flora and fauna from growing and thus reducing the ability of indigenous, native plants from growing. As the plant can grow to 10 or 12 feet high, with large leaves and dense cover, it can reduce the useable area of a garden therefore cause the loss of quiet enjoyment of a property.

Japanese Knotweed Damage to Drains and Other Buried Services

Knotweed roots can exploit existing cracks and gaps in the pipes in their search for water, which will further damage and, in some cases, block the drains. Large, densely packed roots and rhizomes of Japanese knotweed can disrupt drain runs. In the worst cases, the drains must be renewed.

Japanese knotweed damage to electricity cable underground
Knotweed growing through electrical cabling underground.
Japanese knotweed growing in an underground drainpipe
Japanese knotweed growing in an underground drainpipe.
Japanese Knotweed Invading Patios, Paths and Drives

Japanese knotweed can grow between paving slabs and brick or block paving and the expansion joints of concrete drives and paths.

Japanese knotweed damage to paving
Knotweed surfacing through a slabbed patio.
Japanese knotweed growing through tarmac
Japanese knotweed growing through tarmac.
Japanese Knotweed Damage to Boundary and Retaining Walls/Fences

Closely packed stands can undermine garden walls with shallow foundations and old or poorly constructed fences. The mass of the stands can ‘push over’ retaining walls/fences, often resulting in sudden collapse.

Japanese knotweed damage to boundary wall
Damage to a retaining wall caused by Japanese knotweed "pushing over" the wall.
Japanese knotweed growing through tarmac
Cracked wall caused by Japanese knotweed growth.

Vigorous stands of Japanese knotweed that are left to grow will overwhelm lightweight, unsubstantial and poorly built outbuildings/garages and garden sheds, greenhouses etc.


Although the effects will be similar to those described for outbuildings, owners, valuers and surveyors usually attribute greater importance to these structures.

Japanese knotweed damage to shed
Japanese knotweed overwhelming a garden shed.
Japanese knotweed damage to shed
Damage caused by knotweed is visible after Japanese knotweed clearance.

The invasive nature of the plant will ruin a garden or soft landscaped area. The amenity use of an outside space will be lost.

Japanese knotweed damage to garden
Japanese knotweed undergrowth. It's dense and very invasive.
Garden completely destroyed by Japanese knotweed
Garden completely destroyed by Japanese knotweed.
House and Home

According to the Environment Agency’s “The Knotweed Code of Practice”, Japanese knotweed rhizomes can extend up to seven metres horizontally and three metres vertically from the last sign of visible surface growth.

This means that even if there is Japanese knotweed on your property a few metres from your house, the rhizome network could already be under your patio or house. Once it’s spread under your house, it can exploit small access areas and invade your home.

Japanese knotweed growing in house
Japanese knotweed growing through the floor boards in a house.
Car workshop with knotweed growing inside through the wall
Car workshop with knotweed growing inside through the wall.

Japanese knotweed is NOT to be ignored

If you suspect you have Japanese knotweed on or close to your property, but you’re not sure of the extent of its’ growth, contact us and we can help.

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