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Green shovel shaped leaves of Japanese Knotweed

Japanese Knotweed in Sussex, Surrey and Hampshire

Japanese Knotweed (Fallopia japonica) is a rapidly spreading and fast-growing weed.  It was originally introduced to Britain as an ornamental garden plant but is now considered to be an invasive non-native species which is controlled by special legislation.

In winter the plant dies back to ground level and often cannot be detected at all, especially if growth from the previous year is removed.  However, underground the rhizome, a creeping flat mat of intertwined stems, continues to thrive and puts out sideways shoots and roots.

By the late spring, the stems turn vertical and start to re-emerge.  First indications are a reddish-purple fleshy shoot emerging from a crimson-pink bud at ground level.  These then grow rapidly and by mid-summer produce dense stands of sturdy canes which grow to be in excess of two metres tall.  These canes are often mistaken for bamboo but have characteristic purple flecks and produce alternating branches from nodes along its length.

Young shoot breaking up above ground

The leaves alternate along the stem in a zig zag pattern.  They are typically quite broad with a shovel or heart shape to them and can reach a length of 14cm in length.  In late summer, when in flower, the creamy-white flower tassels can descend up to 15cm.

Green shovel shaped leaves of Japanese Knotweed
Leaves on reddish stems alternating in a zigzag pattern

Under the provisions of Schedule 9 of the Wildlife and Countryside Act 1981, it is an offence to cause Japanese knotweed to grow in the wild.  Since 2013, the seller of a property is required to state whether Japanese Knotweed is present on their property by completing the TA6 Property Information form.  As the seller you must check your garden for Japanese Knotweed and the TA6 form asks you to confirm whether your property is affected and, if so, to provide a management plan for its eradication.

As the buyer, you will see on the TA6 form that Japanese Knotweed is present.  It is then likely that your mortgage lender will require details of the eradication plan and may temporarily refuse to lend on the property.  A management plan by a professional eradication company, backed by a transferable guarantee, is usually sufficient to release the mortgage funds.  It is most common for this plan to be provided by the seller before the purchase is completed.

Further legislation, the Anti-social Behaviour and Policing Act 2014, also included regulations regarding the control of invasive non-native plants which could result in the owners of properties affected by Japanese Knotweed being prosecuted for failure to control an outbreak.

Control of a Japanese Knotweed outbreak is considered to be extremely difficult and can result in a detailed eradication plan.  Disposal is not simple as it is classified as controlled waste and cannot simply be sent to landfill and contractors must be specially registered waste carriers.

For the homeowner, it can often take three or four growing seasons to completely eradicate a Japanese Knotweed outbreak with weedkiller as the underground rhizome mat is particularly resilient.  Specialist contractors have access to more potent weedkillers and may be able to reduce this timeframe.  The Royal Institution of Chartered Surveyors (RICS) together with the Property Care Association (PCA) have established the Invasive Weed Control Group (IWCG) trade body for Japanese Knotweed specialists, which provides a register of vetted consultants and contractors.

You should note that there are a number of plants that look quite similar: some bamboos resemble Knotweed in the autumn and winter, then, during the growing season, Fallopia baldschuanica (Russian vine), Leycesteria Formosa (Himalayan honeysuckle), Houttuynia cordata (heart-leaved houttuynia) and Persicaria microcephala (red dragon) can often be mis-identified.

Japanese Knotweed outbreaks are being reported more and more often.  London is a particular hotspot, but outbreaks have occurred all over the UK including Sussex, Surrey and Hampshire.  Notably, Japanese Knotweed has been reported in Brighton, Shoreham, Lancing, Littlehampton, Bognor Regis, Chichester, Portsmouth, Southampton, Reigate, Dorking, Guildford, Epsom and others.  The photos above were taken by one of our surveyors inspecting a property located in Worthing.

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