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Japanese Knotweed

What is this seemingly innocuous plant that is affecting so many home owners and causing untold distress?

A member of the Buckwheat plant family Polygonaceae, Japanese Knotweed is widely recognised as the single most invasive species of plant growing in the UK today. Originally native to Japan, China and Korea, it is believed to have been introduced to Britain by a Victorian horticulturalist in 1824 both as cattle feed and as a decorative shrub. Nearly two centuries later this large, herbaceous perennial is abundant throughout the UK and causes millions of pounds worth of damage every year.

What issues does Japanese Knotweed cause?

Many issues unfortunately, Japanese Knotweed is listed by the World Conservation Union as one of the world’s 100 Worst Invasive Species, such is its resilience. Dormant rhizomes can survive temperatures of -35°C then re-sprout vigorously the following spring. Cutting the rhizome only results in a hearty reappearance of new shoots. Starving the plant of water has zero effect, and regular domestic toxic weedkillers have little effect.

The roots and stem growth of the plant itself damages building sites, foundations, walls, drains, buildings, paving, roads, flood defences, road surfaces – the list is endless. It also harms entire ecosystems as its dense clusters completely crowd out any other existing herbaceous species and wildlife. Typically regeneration occurs during the spread of Knotweed contaminated soil when a site is developed, as less than 1cm of the rhizome can quickly sprout into a viable new plant.

Site owners can expect a reduction in land value and it is normal for mortgage lenders to refuse a mortgage for a property where Japanese Knotweed is present or known to be growing on adjacent land (valuation surveyors are trained to spot Knotweed for this very purpose). It is then necessary to provide proof that the infestation is being dealt with by a professional eradication programme for a mortgage to go ahead, and often the costs involved are subtracted from the value to be loaned on the property. Similarly, planning permission for sites or building developments is likely to be refused without first evidence of a recognised eradication programme being in place.

Watch the video below for a deeper understanding of the problems Japanese Knotweed can cause:

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Gavin White
About the author

Gavin White

Gavin is an experienced and trusted building preservation and restoration professional with over 40 years of expertise in the field. He is the founder of the Preservation Company, which he established in 2009, and holds certifications in CSTDB, CSSW, and SWD. His dedication to preserving and restoring historical buildings has earned him a reputation as a highly skilled and respected professional in his industry.

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