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Throwback Thursday: What is Japanese Knotweed & how do you identify it?

3 Jul 2014
Throwback Thursday: What is Japanese Knotweed & how do you identify it?

It was while watching an episode of Sarah Beeny’s show “Help My House is Falling Down” that I first became aware of Japanese Knotweed. A plant with large, glossy green leaves and a bamboo-like stem, Japanese Knotweed was introduced to the UK by the Victorians who thought that the plant would look lovely in the garden. However, in its native Japan, this weed has 200 predators who feed off the plant and keep it in check. But here in the UK, it has no such enemies. Because Japanes Knotweed grows extremely quickly and has deep and wide spreading roots, the plants can quickly spread and take over a property.

In fact, the weed is so strong that it can grown through tarmac and paving areas. It can damage building foundations and retaining wall structures which can compromise the structural integrity of the property.

This silent video shows the growth of Japanese Knotweed using time lapse photography and it is sobering to watch it plow up through tarmac and paving stones.

But that’s not all – Japanese Knotweed could be a nightmare for homeowners or landlords if you are unlucky enough to find it on your property as it could also mean:

1) Mortgage companies may not lend on the property if it is found – So if you try to remortgage or sell your property Japanese Knotweed may mean you have trouble finding funding.

2) Japanes Knotweed can down-value your property – Due to the amount of time, effort and money needed to eradicate Japanese Knotweed and due to the damage it can cause to buildings, the presence of the weed on your property could mean that your property will be valued at significantly less than it would have been without the presence of the plant.

3) You could be prosecuted – While it is not against the law to have Japanese Knotweed on your property, it can be a problem if you allow the infestation to spread to your neighbour’s property or to wild areas.  It will be a particular problem if Japanese Knotweed damages neighbouring properties and you could be sued.  There are two pieces of legislation that cover Japanese Knotweed. Firstly, it is against the law to plant or “cause to grow” the species. Secondly, Japanese Knotweed is a controlled waste and therefore the plants or even soil containing rhizome material can be regarded as contaminated and, if taken off the site of your property, must be disposed of at a suitably licensed landfill site and buried to a depth of at least 5 metres. To remove the weed from your property you need to also have the appropriate paperwork, so many people choose to burn it on site. Find out more about the legalities of Japanese Knotweed here.

How do you identify Japanese Knotweed?

Japanese Knotweed looks different according to the season.

In spring look for:

– new shoots purple in colour

– appearance not unlike asparagus spears

– leaves begin to unroll and the plant turns green

– growth is rapid and mature canes can reach 3 metres (10 feet) in height

– mature canes are hollow and have a characteristic pattern of purple speckles

– leaves are arranged on stems in a zig zag pattern

In summer look for:

– height of 2-3 meters

– stems have bamboo like appearance and are hollow

– stems are green with red specks and leafs on the stems grow in a zig-zag pattern

– leaves also have quite a distinctive shape with a pointed tip and a straightened edge

– August through October the plant will have tiny white flowers.

In winter look for:

– the canes die off and the plant becomes dormant

– shoots maybe visible for the new growing season

– canes lose their leaves and turn dark brown/red in colour

– dead canes remain standing and may take up to 3 years to decompose

– piles of dead canes may suppress competition from native flora and garden plants.

How Do You Get Rid of Japanese Knotweed?

Japanese Knotweed is notoriously difficult to get rid of.  The London Olympic site was infested with the weed and it took four years to rid the area of the plant.  Because Japanese Knotweed grows so quickly and has such extensive root systems it can take several years to get it under control.  The best thing is to keep an eye out for it and get it treated professionally as soon as you identify it.

Most people agree that hiring a professional to treat the weed is the best option.  Particularly as disposal of the plant is controlled and you don’t want to risk a prosecution or a re-infestation because of improper disposal.

There May Be Hope For A Natural Solution

The following BBC One video discusses why Japanese Knotweed is such a problem and shares a possible natural solution to the problem that may be available in the future:

If you want to know how much your property is worth right now, call our team on 020 8799 3371 or click the link to request your property valuation online.

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