Japanese knotweed in Groby

Knotweed in Spring                                       Knotweed in Summer                                                      Knotweed in Autumn

Should we panic over Japanese knotweed?

Useful links

Government guidance https://www.environetuk.com A flora of Groby parish (Edith Hesselgreaves)

The Royal Institution of Chartered Surveyors (RICS) guide for residential property

Getting a mortgage with Japanese knotweed (Which report)

June 2022  Environet UK, a Japanese knotweed removal company, has identified Leicester as a hotspot for the invasive species.  The Leicester Mercury recently pointed out that it grows rapidly in the UK,  and can damage the foundations of homes and other buildings.  It added that, according to Environet UK, there have been 47 infestations in Leicester already this year and 15 cases in Groby.

There’s no doubt it has to be taken seriously.  “Japanese knotweed tends to strike fear into the hearts of homeowners,” said Nic Seal, founder of Environet, “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 hotspots  we hope to raise awareness and encourage people  to be vigilant for signs of knotweed as the growing season takes off, so they can act quickly. Anyone living near  would be wise to check their garden carefully, and can check our map online to find out how many known occurrences are nearby.”

When the map was checked it only showed  5 cases within 4km of Groby, so Environet’s Mat Day checked it out, using a central Groby postcode.  “From using the postcode I can see 14 reports of knotweed occurrences,” he said. “The map  can show ‘other’ occurrences if the mouse is hovering over another area of the map.   It may be comforting to readers to know that Groby is relatively unscathed by knotweed thankfully. The occurrences noted pick up a number of cases from the Glenfield/Ratby area.”

What to look out for 

The reason homeowners are so wary of Japanese knotweed is the ease with which it spreads and the damage it can wreak if not effectively dealt with.  Japanese knotweed dies back in winter, making it harder to spot.  In early spring Asparagus-like spears emerge from the ground, 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.

It roots help it spread

The roots of Japanese knotweed are a huge problem and can grow as deep as 3 metres which makes it  difficult to get rid of. The roots can also spread up to 7 metres horizontally. While the above-ground infestation is fairly easy to get rid of, it's the roots underground that cause the biggest problem.  They can grow too deep for most normal gardening and digging practices which is why it's important to combine this process with chemical knotweed control. 

Even one rhizome remaining in the ground means that the plant will start to grow again.  Japanese Knotweed spreads via dispersal of its rhizome fragments, stems and crown.  This can happen accidentally or intentionally.   A plant can grow from a fragment of rhizome fragments as small as 10mm, therefore, if any soil beneath a knotweed patch is moved or dumped, a new crop can be expected to grow on the new site.

A legal obligation to stop it spreading

While it is not illegal for you to have knotweed on your property, it is against the law to cause or allow the plant to spread - meaning you should probably take action if it's on your land. The Wildlife and Countryside Act 1981 [4] is just one of a handful of laws that  demonstrates how seriously it deals with those who negligently cause it to spread.

Some, with a minor infestation may decide to tackle the problem themselves, and as this is not the first time the weed has been spotted in Groby there are precedents for successful DIY treatment.

Spraying or injecting the stems with approved herbicides can be an effective treatment to stop knotweed spreading.  You’ll have to respray, as it usually takes at least 3 years to treat Japanese knotweed. Knotweed rhizome can remain dormant in the soil for many years and will regrow if disturbed or if the soil is relocated.

You can dispose of the dead brown canes of Japanese knotweed by composting on site, as long as they’re cut (not pulled) a minimum of 10cm above the crown, but you must notify the Environment Agency at least one month before you bury the knotweed.  You’ll need a Masterclass in digging, as you must bury knotweed material:

    • on the site it came from, including ash and soils at a depth of 

    • at least 5 metres if you have not sealed it with a geotextile membrane,

    • at a depth of at least 2 metres, if you have sealed with a geotextile membrane.

Because of all the complications you may prefer to employ Environet, or one of the other specialist companies, to resolve the matter for you. Unlike many other trades there are no long waiting lists. “From initial contact, we can have a consultant out within a few days surveying the property, from which a Japanese knotweed Management Plan is issued within 48 hours,” explained Mat.  “Then we can remove the knotweed in a matter of weeks, with works usually only taking days to complete.”

It's not a newcomer to Groby

Knotweed is far from being new to Groby, and was recorded by the late Edith Hesselgreaves when she conducted her definitive botanical survey of the village 50 years ago.  She found it growing by the air-pump of the Bluebell garage (now the Co-op Leicester Road store), on the path near Martinshaw school and along the A.50 roadside on Bradgate Hill.  The Bradgate Hill reference is intriguing.  Bradgate House, with it’s stunning stables and perhaps a garden to impress, was built in 1856, just six years after the plant hunters introduced Japanese knotweed as an exotic must-have to the UK.  Pure speculation, but interesting.

If you spot the plant on your property  then June and July is suggested as the best time of the year to deal with it.  If you rent an allotment you should contact the Allotment Society Secretary if you think you have a problem. You’ll find plenty of advice online, including some links above, and should seriously consider how you deal with it.

Photos - Environet.com