Dorset residents advised to look out for Japanese knotweed

DORSET residents who are spending more time than usual in their gardens during the current lockdown may be concerned to discover red asparagus-like shoots appearing as Japanese knotweed enters its spring growth phase.

A heat map has been launched by knotweed experts Environet UK to provide a comprehensive live record charting the spread of the UK’s most invasive plant across the country.

This has identified some hotspots in Dorset, with 42 infestations within a four-mile radius of Charmouth, 26 near Lyme Regis, 24 around Dorchester, 15 at Weymouth  and 14 in Christchurch.

Homeowners in these locations should be vigilant during April when knotweed starts to grow rapidly, turning from red to green before forming hollow bamboo-like canes. By late spring it is covered in attractive heart-shaped green leaves. 

Described by the Environment Agency as “indisputably the UK’s most aggressive, destructive and invasive plant”, Japanese knotweed grows rampantly along railways, waterways, in parks and gardens and is notoriously difficult to treat without professional help.

It can reduce a property’s value by around 10% and make it difficult to sell unless a treatment plan is in place with an insurance-backed guarantee, which will satisfy mortgage lenders.

According to Environet UK, approximately four to 5% of the UK’s houses are currently affected, either directly or indirectly (e.g. neighbouring a property where it’s present) but despite the plant’s fearsome reputation, homeowners should not panic if they find themselves in lockdown with this unwelcome guest.

Environet offers the following advice:

  • Identify any suspicious plants – Japanese knotweed starts growing rapidly in March and April, when red spears emerge from the ground, turning green before forming hollow canes. If you’re not sure what you’re looking for, email a photo to for free identification. Plants commonly confused for Japanese knotweed include Bindweed, Russian Vine and Ivy.
  • In most cases knotweed can be dug up during the lockdown period – As the work is undertaken outside and there’s no need for a treatment professional to enter a property, it’s still possible to excavate knotweed as long as social distancing measures can be safely observed. Contact a professional removal firm and arrange a remote survey using Facetime or by sending photographs.
  • Don’t panic if this is not possible – For example at a terraced property with limited rear access. Homeowners can still make arrangements to have the invasive plant removed when restrictions are lifted and the work will typically only take a couple of days. While it’s always best to treat or remove Japanese knotweed as soon as possible, in most cases it won’t do too much harm to leave it happily growing for the next few weeks.
  • Herbicide treatments don’t take place until early June anyway, when the plant is in full leaf – Make arrangements now for peace of mind and to ensure you’re at the front of the queue.
  • If you’re hoping to sell your home, use this time to deal with the problem and secure a 10-year insurance-backed guarantee for the work, to help your sale progress smoothly once lockdown is over. Sellers are legally obligated to inform buyers if a property is or has been affected by knotweed and could be sued if they fail to do so.
  • Don’t be tempted to tackle Japanese knotweed yourself – Methods attempted by homeowners to kill the plant include mowing it, covering it to deny sunlight, setting fire to it, dousing it in bleach or petrol and even electrocuting it! But none of these measures are effective at killing the plant’s vast underground root system and you could inadvertently aid its spread. Plus, Japanese knotweed waste can’t be put in a green bin. It’s classed as controlled waste and needs to be disposed of at an authorised landfill site.

Nic Seal, founder and MD of Environet, said: “Our message to homeowners who discover Japanese knotweed growing in their garden over the next few weeks is not to panic and resist the temptation to deal with it themselves.

“In most cases knotweed can still be removed during the lockdown period, but if this isn’t possible it won’t make a huge amount of difference to leave the plant growing until restrictions are lifted. A failed attempt to dig it up could help it spread and spraying the plant with herbicide makes professional treatment more difficult further down the line.”

Environet’s heat map is a free online tool for anyone seeking information on the spread of knotweed in their local area. Users can enter their postcode to discover the number of reported cases nearby, with hotspots highlighted in yellow or, in the most severe cases, red.

The public is also encouraged to help populate the heat map by reporting knotweed infestations using the ‘Add Sighting’ feature and attaching a photograph of the plant so it can be verified by experts.

The heat map can be found online at More than 93,000 postcode searches have been undertaken since its launch in spring 2019.

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