Greenhalgh & Co.

Chartered Building Surveyors & Valuers

Greenhalgh & Co.

Chartered Building Surveyors & Valuers

21 Towncroft Lane

Bolton  BL1 5EN

Tel: +44 (0)1204 845382

Mob: +44 (0)7813 439196



RICS Company No. 002973


Loss of value due to Japanese Knotweed


Japanese Knotweed was considered an attractive garden plant when it was first imported to the UK in the nineteenth century.  


Knotweed (scientific name Fallopia Japonica) can damage hard surfaces such as tarmac, grow through the floors of houses, occasionally even through the foundations and, as a result of this vigorous growth can exclude almost all of our native species. It is a highly invasive perennial weed, growing to a height of up to 3m, and comprising bamboo-like stems with a purple speckled appearance. Dense areas of tall canes grow during summer and then die back in the autumn. Creamy white flowers appear late in the season. Once present on a site, it grows quickly if left unchecked to cover large areas. During later autumn and winter the canes die off losing their leaves and turning dark brown. The dead canes remain standing, and can take up to three years to decompose, often forming a dense organic layer which suppresses competition from native flora.


In the UK, the reproduction of Japanese Knotweed is mainly through vegetative regeneration of rhizomes and fresh stems. The rhizome is a root-like underground stem which can reach a depth of 3m and extend up to 7m away from the parent plant.


Japanese Knotweed is not an easy plant to control. Unfortunately the extensive underground rhizome system sustains the plant even when the plant above ground is removed. So, the aim of any control programme must be to target the rhizomes. One way of achieving this is the use of chemical treatments, for example herbicides such as glyphosate.


The use of such chemicals can require consents from the Environment Agency, particularly in areas where there may be a risk of run-off to water courses, or where there is adjacent sensitive vegetation. Treatment can take several years before the plant is completely eradicated and during this period continuous monitoring is necessary to check that no new shoots appear.


The costs associated with removing Japanese knotweed are often around £75.00/m2.


But there are two sides to the Knotweed coin.  Japanese Knotweed is edible raw or cooked — young shoots, growing tips of larger plants and unfurled leaves on the stalk and branches. People say it tastes a bit like rhubarb. For the health conscious it is a major source of resveratrol and Vitamin C.


Japanese knotweed does feature in the Wildlife and Countryside Act 1981 as amended by Statutory Instrument 609 of 2010.


In this amendment a series of plants listed as invasive species.

And the act states that:

(2)Subject to the provisions of this Part, if any person plants or otherwise causes to grow in the wild any plant which is included in Part II of Schedule he shall be guilty of an offence


The list is not a short one, and surprisingly there are some favourite garden plants on it, for example: Cotoneaster, Yellow Azalea, Montbretia, Rhododendron, and Virginia Creeper.


Unfortunately for Japanese Knotweed it has been singled out as pest and the majority of people require a discount if it is found growing in or adjacent to a domestic property.


The rights and wrongs of singling out Japanese Knotweed as opposed to Himalayan Balsam (which is arguably more invasive) or dandelions, which are probably close to the top of the gardener’s hit list is debatable. 


However the popular press and therefore the public has singled out Japanese Knotweed, and for that reason a discount is often considered.


In our opinion up to 5% is appropriate.

Japanese knotweed