Japanese Knotweed – The housebuilder’s nemesis!

Frequently referred to as ‘the curse of gardeners everywhere', Japanese Knotweed has always been known as a formidable plant, especially amongst housebuilders. The plant, a tall and vigorous non-native invasive species, was introduced into the UK as an ornamental garden plant in the mid-nineteenth century. It is a distinctive looking plant with bamboo-like stems which flowers between August and October and now spreads wildly across the UK.

Japanese Knotweed causes frequent problems in the housebuilding industry. Before work can commence on site, the plant needs to be dealt with to ensure it does not grow back again and subsequently cause damage to any property.

There are a number of ways in which Japanese Knotweed can be managed and controlled, which include:

- Excavation of all knotweed material and disposal in an appropriate landfill facility
- Treatment of the plants with a recognised herbicide
- Protection of structures using a root barrier membrane

In Camborne, Midas Homes is working with English Partnerships on a scheme that will provide 390 homes for the local community. However, the site has also become the largest Japanese Knotweed eradication project ever undertaken in the UK. Over £2million is being spent on removing the plant from the site and it is a time-consuming and laborious process.

This project saw attempts at conventional systems render the Japanese Knotweed ‘untreatable'. The vast chemical use over a sustained period could have removed the palatability of the plant to insect attack - in short, none of the systems would be viable. If you'd listened to all the experts then there were two options: either wait five years to build the homes or remove 70,000 cubic metres of material to landfill at a cost estimated to be in the region of £5million.

Were these the only options available then this project would not have commenced and the land would probably never have been purchased; losing the prospect of vital jobs, houses and a crucial boost to the local economy.

TCM (Thurlow Countryside Management) was employed to eradicate the Japanese Knotweed invasion at Camborne where they have adopted an excavation and screening process. Nick Hartley from the company said: "We have been operating for over eight years, in which time over 2000 sites have been successfully treated and eradicated. We are pleased to be working with Midas Homes on such an exciting project in Camborne and continue to look for innovative ways to remove Japanese Knotweed."

Graham Hutton, Midas Homes' Technical Director commented: "Japanese Knotweed has certainly been our nemesis on many occasions. However, we have managed to overcome the problem and although it is a costly and time-consuming process, we are pleased that we've taken control over it - allowing us to select land for development based on location and not whether it's free from Japanese Knotweed!"

Housebuilders 1 - Japanese Knotweed 0!