Environet: How close is Japanese knotweed to your home?
10 May 2022: As the Japanese knotweed growing season gets underway, invasive plant specialist Environet UK reveals the knotweed hotspots for spring 2022 using data from its interactive online tracker, Exposed: The Japanese Knotweed Heatmap.
Populated with almost 55,000 known occurrences of the UK’s most invasive plant, Exposed is the most comprehensive online record of knotweed infestations, charting the spread of the plant across the country. Users can enter their postcode to discover the number of sightings nearby, with hotspots highlighted in yellow, orange and, in the worst cases, red. The map enables homeowners to understand the risk knotweed poses to their home, or one they wish to buy.
The Great Britain Japanese knotweed hotspots for 2022 are:
|Rank||Location in Great Britain||Infestations within 4km radius|
|1||Bolton, Greater Manchester||684|
|3||St Helens, Merseyside||441|
|5||Capel Garmon, Snowdonia, Wales||398|
|6||Llanelli, South Wales||389|
|9||Streatham, SW London||300|
Japanese knotweed first arrived in UK in 1850 in a box of plant specimens delivered to Kew Gardens. Favoured for its rapid growth and pretty heart-shaped leaves, it was quickly adopted by gardeners and horticulturalists who were oblivious to its invasive nature. Knotweed hibernates over winter but in March or April it begins to grow, with red or purple spear-like shoots emerging from the ground which quickly grow into lush green shrubs with pink-flecked stems and bamboo-like canes.
For homeowners, the plant can pose serious problems if left unchecked, with the potential to grow up through cracks in concrete, tarmac driveways, pathways, drains and cavity walls. The roots can grow as deep as 3 metres and spread up to 7 metres horizontally. While serious damage to property is rare thanks to regulation which requires knotweed to be dealt with when a property is sold to a buyer using a mortgage or if it encroaches across a garden boundary, it commonly impacts use of the garden, causes legal disputes between neighbours and can impact a property’s value by around 5%.
Homeowners and buyers who are unsure whether a property is affected by knotweed can now call in help from a specially-trained trio of sniffer dogs, Mick, Mack and Buddy, who will search a property for the unique scent of the plant’s rhizome even where it’s dormant beneath the ground or has been deliberately concealed.
According to Environet’s research, approximately 5% of homes are currently affected by knotweed, either directly or indirectly, but sales can proceed as long as a professional treatment plan is in place with an insurance-backed guarantee to satisfy mortgage lenders.
Nic Seal, founder and Managing Director of Environet, said:
“Japanese knotweed tends to strike fear into the hearts of homeowners but as long as they’re aware of its presence and take action to remove it before it causes any serious damage or spreads to a neighbour’s property, there’s no reason to panic.
“By publishing the 2022 British Japanese knotweed hotspots we hope to raise awareness and encourage people in the area to be vigilant for signs of knotweed as the growing season takes off, so they can act quickly if needed.
“Anyone living near or moving to one of these hotspots would be wise to check their garden carefully, enter their postcode into Exposed to find out how many known occurrences are nearby and if in doubt, seek expert help.”
Spring 2022 Japanese knotweed hotspots in Great Britain (Credit: Environet UK):
How to spot Japanese knotweed:
- Asparagus-like spears emerge from the ground in early spring and begin to sprout pale green leaves with distinctive pink veins
- In May the plant starts to grow rapidly. The stems harden into bamboo-like structures and the leaves, which grow in a zigzag pattern up the stem, are lush, green and heart-shaped
- By mid-summer the plant grows at a rate of around 10cm per day, with mature plants forming dense stands two or three metres tall
- In August the plant blooms, with small clusters of creamy white flowers appearing on the upper leaf axials.
What to do if you think you have Japanese knotweed:
- If you find a suspicious-looking plant and you’re not sure what it is, check out the identification guide on Environet’s website or use the free ID service by sending a photo to email@example.com
- Once knotweed is confirmed, commission a professional Japanese knotweed survey to find out the extent of the infestation, where it originated and the best way to tackle it
- Arrange professional treatment, usually herbicide or excavation, and always be sure to secure an insurance-backed guarantee for the work
- Sellers are legally obliged to tell any potential buyer if a property has been affected by knotweed, even if the infestation has been treated
- It’s not illegal to have knotweed on your land, but you will be liable if you allow it to spread to someone else’s property through inaction
- If you’re buying a property and you want to be sure it’s clear of knotweed, particularly if it’s located in or near a hotspot, arrange a detection dog survey.
To view Japanese knotweed infestations in your area or to report a sighting by uploading a photo to be verified by experts, visit here.
Kindly shared by Environet UK
Main article photo courtesy of Pixabay