Revealed: Norfolk's hotspots for Japanese Knotweed in 2021

The fast-growing, invasive, plant Japanese Knotweed or 'or as it is also known, Polygonum cuspidatum

The fast-growing, invasive plant species, Japanese knotweed, can affect property prices - Credit: Getty Images/iStockphoto

Now that summer is officially here, sightings of one of the UK's most invasive species of plant are expected to soar - and several places in Norfolk have been identified as hot spots.

Throughout spring, Japanese knotweed emerges from the ground as purple or red asparagus-like shoots, before growing into lush green shrubs with heart or shovel-shaped leaves. It can grow up to 10cm a day between May and July and by mid-summer reach heights of around three metres. 

Japanese Knotweed expert, Environet, has created a live online tracker to help people locate and record the pest plant.

According to the tracker, the area around Trowse, with the postcode NR1 2EN, has recorded 79 occurrences of Japanese knotweed within a 4km radius, followed by 68 in Norwich (NR1 1RE) and 67 in Caistor St Edmund (NR14 8QN).

Map of East Anglia with orange and yellow hotspots identified to depict Japanese knotweed sightings

Environet's live tracking map, which helps people to record sightings of the invasive plant Japanese knotweed - Credit: Environet UK

At least 40 occurrences within a 4km radius have also been spotted in Sprowston and at least 25 in the area between Salhouse and Rackheath.

According to Environet's research, approximately 5% of homes across the country are currently affected, knocking around £20 billion off UK house prices. 

And while it's not illegal to have Japanese knotweed on your property, you should aim to control it. Homeowners looking to sell are expected to declare it and provide a management plan.

Environet say that the general public can help in the fight against knotweed by reporting suspicious plants using the heatmap’s ‘Add Sighting’ feature and attaching a photo to be verified by experts. 

Japanese Knotweed invading wetlands areas in the countryside

Japanese knotweed can grow up to 10cm a day between May and July - Credit: Getty Images/iStockphoto

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Users who want to check on an area can simply enter a postcode to discover the number of reported knotweed sightings nearby, and hotspots are highlighted in yellow or red, like a traffic-light system.

"Knowledge is power when it comes to Japanese knotweed and this heatmap is invaluable to homeowners and buyers who want to assess the risk in their local area," says Mat Day, Environet's regional director for East Anglia.

Mr Day says that despite its fearsome reputation, the plant can be dealt with - but it's best to seek professional help.

While it may be tempting to dig out the plant at root level, disposing of it can be challenging, as it's classed as 'controlled waste' under the Environmental Protection Act 1990, and therefore requires disposal at licensed landfill sites. It should never be included in normal household waste or put out as part of green waste collection schemes.

Fallopia japonica or Japanese knotweed. Branch with green leaves and white flowers

According to Environet's research, approximately 5% of homes across the country are currently affected, knocking around £20 billion off UK house prices. - Credit: Getty Images/iStockphoto

Back in May, Environet revealed its list of Japanese knotweed hotspots for spring across the country. Bolton in Greater Manchester came top of the list, with 621 infestations within a 4km radius, followed by Bristol with 465 and St Helens in Merseyside with 440.

What is Japanese knotweed?

Japanese knotweed was brought into the UK in the 1840s, as part of a shipment of 40 boxes of Chinese and Japanese plant species delivered to Kew Gardens. It was intended to be an ornamental garden plant, but has since become an invasive non-native species, which needs to be controlled.

Identification is important, though, because it can easily be confused with other plants, including Russian vine and Himalayan honeysuckle.

According to the RHS, Japanese knotweed rarely sets seed in this country but can sprout from very small sections of creeping underground stems, known as rhizomes. It is an offence to cause it to grow in the wild.