Japanese Knotweed

In the last 5 years, there has been an increase 28% of Japanese knotweed according to nbnatlas.org data.  The plant is classified as one of the top invasive species by the World Conservation Union. Having the plant on or near your property may also result in an inability to get a mortgage.

What is Japanese Knotweed?

A recent survey by horticulture.co.uk found that 47% didn’t recognise the plant when shown a picture. In fact, one in twelve didn’t even know what the plant was.

identifying the plant

If you are ever unsure it is always wise to seek a professional opinion.

The plant goes through a couple of different stages as it’s a bit more dormant in the winter. Winter is normally the ideal time for a treatment.

Leaves

  • New leaves are red and a bit rolled up and around 1-4cm long
  • Young Leaves have red ‘veins’ and are green and slightly rolled
  • Mature leaves are spade-shaped or (sometimes compared to a shield) heart-shaped. They are flat and 12cm long

Stems

  • Bambo like main stem
  • The stem is hollow and can normally be easily snapped.
  • Zig-zag growth with leaves
  • Early spring (red) buds start to come up through the ground.

Flowers

  • Blooming in late summer
  • Creamy white 
  • Clustered flows around 10cm

History of (Fallopia Japonica) Japanese knotweed 

Philipp Franz von Siebold Originally bought to the UK from Japan (you might’ve guessed the originating country by the name) in the mid 19th century.  It might’ve seemed like a good idea at the time and was highly praised by to be the “most interesting new ornamental plant of the year” by the Society of Agriculture and Horticulture at Utrecht in Holland. 

The plant was popular over the Victorian age, it was widely sold through nurseries and was popular and fit well with the decadent Victorian style. Unfortunately like all fashionable things inevitably the plant went out of style, so like many things it went into the bin, the compose, thrown over fences in all sorts of places. Knotweed is a resilient plant and so all that did was spread it far and wide to be the pest that it is today. In fact, to completely eradicate the plant would cost billions, the plants already removed over £20 billion from property value alone.

Removal & treatments

It is advised to get specialists to help with the removal and disposal of the plant which will need to be reapplied over several years. Failure to properly removal can result in the plant regrowing, the plant can regrow from a (0.8g) fingernail-sized rhizome. It is illegal to allow the plant to grow outside your property or into the wild. It’s best and normally most cost-effective to treat the plant as soon as possible due to its growth rate. Especially as it can grow 10 cm a day and its roots can penetrate as far down as 3 meters.

Treatments

The weed needs to be dug up though due to the volume of soil this is usually unpractical, Chemical treatments are more common though reapplication is required. New research by the National University of Ireland Galway has found completely drying the plant out (to remove all the moisture) is effective and further tests are on-going 

Eating and drinking it, some people have compared it to rhubarb and others enjoy it in a tea but you’ll have to be pretty hungry. 

How to sell a property with Japanese knotweed?

You may need property information – TA6 form which is usually created when a surveyor visits your property. On this form will be a mention of if there is knotweed onsite or in close proximity but also any eradication plans.

RICS has given new guidance (in 2021) and is currently consulting on further updates to their advice on dealing with the plant.

Quick house sale companies like HouseBuyFast will buy any house even if it has knotweed though it will affect the price due to the action required to tackle the invasive plant. 

If you have any questions or concerns we would be happy to give advice.

 

Jonathan Rolande

Jonathan Rolande began in the property industry in 1987 and has extensive knowledge of the property buying sector. Jonathan is also an avid supporter of greater regulation in the industry. Founding the National Association of Property Buyers to offer essential information to property sellers.