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Japanese Knotweed identification

Japanese Knotweed is an invasive plant that has originated from Japan and nearby East Asian countries.

Japanese Knotweed identification

Japanese Knotweed is an ornamental vine which was originally brought to the UK during the Victorian era. However, due to its lack of natural predators in the UK, the weed has quickly spread across Britain and is causing problems for property owners nationwide.

To ascertain a better understanding of the plant, follow our guide to quickly identifying Japanese Knotweed and deciphering the law surrounding this highly destructive plant.

In its native environment, Japanese Knotweed is kept in check by native insects and fungus that feed on the plant. Outside of its native environment, Japanese Knotweed has become a menace on both residential and commercial properties. It has become prevalent throughout the UK over the course of the last 100 years; with an estimated infestation every 10sq kilometres.

The weed may appear harmless, but it can break through concrete and tarmac causing damage to building foundations and retaining wall structures. This will not only damage the stability of a residence or workplace, but it will also seriously depreciate the property’s value, hinder mortgage loan applications and may affect insurance companies insuring a property infested with Japanese Knotweed.

Did you know? Thousands of Japanese insects called Aphalara itadori, which feast on the weed, were introduced in 2010 in an attempt to stunt its spread.

How do you identify Japanese Knotweed?

There are different types of Japanese Knotweed and during each season their appearance can change, which makes identifying them problematic even for a qualified surveyor. It is important to be able to identify Japanese Knotweed when purchasing a property and the extent of the infestation.

Beth Wheatley, a solicitor for Aaron & Partners Solicitors has extensive experience in dealing with invasive plant species problems, so we asked for tips on the best ways to identify Japanese Knotweed:

Japanese Knotweed can be identified by its white flowers and distinctive bamboo like stems which can reach up to 3 metres in height. When it first breaks through the ground it can be recognised by fleshy, red tinged shoots with large spade shaped leaves.

Did you know? The government estimates it would cost £1.5bn to clear the infestation of Japanese Knotweed in the UK and each year, £166m is the estimated amount spent on treating the plant.

The law and Japanese Knotweed 

If the plant spreads to a neighbouring property or public land, it becomes a criminal offence and could result in a £5000 fine and/or up to six months in prison, depending on the severity of the offence.

According to rules recently proposed by the government, the punishment for neglecting civil responsibility for growth of the evasive plant could become increasingly severe. Anti-social behaviour orders could be distributed as punishments to those who fail to control infestations, with companies guilty of the spread of Japanese Knotweed leaving themselves open to fines of up to £20,000. 

Did you know? Japanese Knotweed can lie dormant underground for 10 years, and it can take up to five years for poison to kill it completely.

Safe and legal Japanese Knotweed removal

There are specific regulations surrounding the removal and disposal of the plant. The legal and safest way of removing Japanese Knotweed is by enlisting a contractor to dispose of the plants, roots and soil to an approved landfill.

As a new plant can grow from a root the size of a finger nail; it is vital that all stages of Japanese Knotweed removal are completed properly, and any Japanese Knotweed waste is transported by a licensed waste carrier. 

Did you know? Japanese Knotweed can grow to a height of 2 to 3 metres in just one season, and only 0.06g of root is needed for the plant to grow again, making it almost impossible to eradicate by digging up.

How can Japanese Knotweed affect mortgages?

Mortgage lenders are legally able to refuse a mortgage on a property which has an infestation of Japanese Knotweed. There are now detailed questions regarding invasive plant species on house sale documents. The seller must answer these truthfully and state whether there is a management plan in place to control the plant, if so a copy of this plan must be included with the property information form.

If Japanese Knotweed is found on a property it can also affect the owner’s ability to obtain buildings insurance. Proprietors do not have to legally declare the presence of Japanese Knotweed on a property to an insurer (unless asked), but they are obliged to control the plan and take the necessary preventative measures towards the weed damaging the building. If the owner makes a claim and during inspection it is found that they have not done everything within their power to control the plant, an insurer has the right to refuse to pay out.

Did you know? It cost £70m to clear the weed from 10 acres of the Olympic Park for the 2012 London Games.

Different types of Japanese Knotweed

Japanese Knotweed (Fallopia Japonica)
Japanese Knotweed or Fallopia Japonica is the most common type of Japanese Knotweed. They have heart shaped leaves and small creamy white flowers. They have one stem per node and have a Zig Zag stem growth pattern. 

Giant Knotweed
Giant Knotweed is similar to Fallopia Japonica but has larger leaves and is taller (up to 4.5 metres).  The leaves are pointed at the tip and grow to about 40 cm long and 27 cm wide.  Creamy white flowers appear in late summer/early autumn in dense panicles. 

This is a hybrid between Fallopia Japonica and Giant Knotweed. The leaves are larger than Fallopia Japonica and heart shaped. Leaves are pointed with veins reddish purple when immature.

Dwarf Japanese Knotweed
As the name suggests, these types of Japanese Knotweeds are small and only reaches 1m – 1.8m in height. Their leaves have crinkled edges and a leathery texture. The leaves vary in shape and are often in concave form. White or pale pink flowers appear in late summer, which often mature to dark pink or red.

Himalayan Knotweed
These types of Knotweeds are less common in the UK. They have slender, elongated leaves and tapered to a point. Can grow to a height of up to 1.8m and the stems are usually green and have a zig zag shape from node to node. They have hairy stems and brown sheaths that persist at the basis of the leaf stalks.

Lesser Knotweed
These types of Knotweed are less invasive but still pose a problem. They can grow to a height of 60-90cm. The flowers are tiny, pale pink bell shaped and produced in clusters on short spikes. The undersides of the leaves are much lighter in colour with small white hairs. They don’t have the distinctive zig zag shape.

Did you know? As well as a good source of vitamin C, Japanese Knotweed is said to taste like rhubarb with a hint of lemon. There’s so much of the plant in Pittsburgh, Pennsylvania that businesses are turning it into beer, ice lollies and honey.
Identifying Japanese Knotweed all year round
Japanese Knotweed will look different throughout the year. As the images below show, it helps to be able to identify what Japanese Knotweed looks like as the seasons change.

The weed spreads quickest during the summer months, where it can grow up to 10cm a day. Luckily, throughout autumn as the weather turns colder, Japanese Knotweed retreats leaving behind brown stems, although as was the case in 2014, new growth was found as late as November.

Did you know? 9.2% of rivers and canals in England and Wales are infested with Japanese Knotweed. In Scotland, it’s 3.1%

Japanese Knotweed can be a major problem for landowners, but it is a treatable problem with the right help. All legal obligations can be followed by employing a specialist contractor who has extensive experience in dealing with invasive weed species.

For professional advice visit japaneseknotweed.co.uk where our highly trained staff are more than happy to help if you have further concerns regarding Japanese Knotweed removal or identification.


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