Japanese knotweed is often cited to be one of the UK's most destructive plants, and it is not to be ignored. However whilst it is true that Japanese knotweed can cause problems to your property if left untreated, help is available. The quicker it's identified and treated, the easier it is to control.
Is Japanese Knotweed Dangerous?
Japanese knotweed is a non-native invasive plant that can cause problems to your property. 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 (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.
However, Japanese knotweed is not dangerous to humans or animals. In fact, it's edible! There are recipes online using knotweed and there are even products such as gin and wine incorporating knotweed. We don't recommend that you harvest knotweed due to its invasive nature and the risk of spreading which can lead to criminal prosecution. Note that it is illegal to transport Japanese knotweed without a Waste Carrier Licence.
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 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 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.
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.
The invasive nature of the plant will ruin a garden or soft landscaped area. The amenity use of an outside space will be lost.
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 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.