Japanese Knotweed

What is Japanese Knotweed?

Japanese Knotweed (Fallopia Japonica) is one of the most invasive Non-native species found in the UK.  It is a large clump forming plant that can grow to almost 3 metres in height.  As the name suggests, it is native to Japan, and was introduced here in the mid-19th century as an ornamental garden plant.

 

Japanese Knotweed is a perennial plant that produces tall canes during the summer growing season.  The canes are easily identifiable as they have distinctive purple flecks along its green stem.  The branches and leaves grow in an alternate zig-zag pattern from nodes along the canes.  The canes die back during the winter, and turn into a brittle hollow dry winter cane.  It can take up to 3 years for the winter canes to break down naturally.

 

The canes grow from an underground rhizome, which forms a dense crown, from which the canes grow.  Studies have shown that these rhizomes can spread up to 7 metres away from the parent crown, and to a depth of 2 metres. 

 

The knotweed can rejuvenate from small damaged sections of the canes, although most of the knotweed found in the UK is as a result of rhizome or crown material.  A finger nail size piece of rhizome weighing 0.7g can regenerate quickly into a new knotweed plant.

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Why is Knotweed a problem?

Japanese Knotweed is an incredibly fast growing and strong plant, it can grow to its full height of almost 3 metres in as little as 10 weeks. The speed of its growth, and dense leaf canopy area, makes it difficult for other plants to grow beneath the knotweed, and very quickly you will find that there is only bare earth beneath the knotweed plant.  

 

This bare earth is particularly a problem on watercourses where during floods, or high tides, the river bank can be eroded away, taking fragments of the crown or rhizome with it, resulting in a risk of spread of the knotweed further down stream.

 

It also has an incredibly sweet tasting nectar, which attracts bees, but this can be an issue as it takes them away from other neighbouring flowers, therefore has a detrimental effect on pollination of other native species.

 

Although it spreads much slower, the rhizome can extend in any direction, and will tend to follow the path of least resistance.  This can cause problems to homeowners, and it can have a destructive effect on building foundations and drains.

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Identification

Japanese Knotweed (Fallopia Japonica) is one of the most invasive Non-native species found in the UK.  It is a large clump forming plant that can grow to almost 3 metres in height.  As the name suggests, it is native to Japan, and was introduced here in the mid-19th century as an ornamental garden plant.  

 

The information below gives a brief explanation of how the appearance of Japanese Knotweed changes throughout the year. 

japanese knotweed shoot early
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JK winter canes (7)

Spring

During March to April, small red/purple shoots (similar to asparagus) emerge from the ground.  As time passes, the leaves begin to open, and they can be red or green with red veins.

Summer

This is when the plant grows quickly.  The bamboo like green and purple speckled hollow stems will grow in tightly formed stands.  The heart shaped leaf with its flat base grows alternatively from zig-zag stems.

Late Summer

During September to October, the plant begins to flower.  Small creamy white flowers, growing on 100mm long stalks,  hang down in clusters.  Even though the plant does produce seeds, the plant does not spread through the seeds.

Winter

After the plant has flowered, the leaves turn yellow, and it begins to die back for the winter.  The leaves fall off, and the stems turn brown and become dry and brittle.  These dead stems can take up to 3 years to break down.

Treatment & Control Methods

Once Japanese knotweed has become established on a patch of land, it can be very difficult to eradicate the problem.  Many landowners attempt to clear the problem themselves, but this often leads to the problem getting worse.  Below you will see different control methods that are used in the eradication of knotweed.

Chemical Control

Chemical control involves the application of herbicides to the plant over a period of several growing seasons.  

This is the most economical treatment option, but can take 3-5 years to be effective.

Excavation

Knotweed infested ground can be excavated, and then removed off site to a licensed waste management faclity.  This is the most expensive option of control as it involves removing a large amount of soil from the site.

On site burial

The Knotweed can be excavated and then buried again on the same site (if space allows).  If it cannot be buried beneath 5 metres or more, then it must be encapsulated with a root barrier membrane.

Biological Control

Biological control involves the introduction of a species that will attack and feed on the plant.  This is not currently a viable treatment method as it is still in the trial phase.

 

Knotweed and Mortgages

If you are thinking about buying or selling a properly and are concerned about Japanese Knotweed please feel free to contact us for some more information.  

 

Many RICS surveyors are now very aware of the issues related to Knotweed and are reporting this back to lenders.  This leads to some lenders refusing to give mortgages for properties affected by Knotweed unless action is taken by a reputable Knotweed Specialist.  

 

As a specialist Knotweed contractor, we can carry out the work required, and provide the evidence needed in order to assist with succesfully buying or selling a property.  This will involve providing a comprehensive site survey and report, and development of a treatment plan.  For more information on this process please see the Services page by clicking here.  

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What to do if you have Knotweed on your property?

Do not attempt to cut, dig up, burn or treat the knotweed yourself, you may make the problem worse.  Get in touch with us by completing the contact form here, and we will be in touch to  arrange a site inspection.