Japanese Knotweed FAQ's | Green Leaf Remediation

Japanese Knotweed FAQ’s discussed by Green Leaf Remediation

Find out everything you need to know Knotweed in our Japanese Knotweed FAQ’s.

What is Japanese Knotweed?

Japanese Knotweed can sometimes be referred to as Fallopia Japonica, Bamboo and Peashooters and it is a perennial weed that grows and can spread quickly from one tiny fragment of crown or rhizome if it isn’t controlled. It’s crown and rhizomes (root system) suppress other plants growing around and it spreads extensively and quickly underground. Well-established shoots can grow more than 3 metres high and can colonize the soil within a few years. In the height of its predominant growing season, 60% of its roots are in the soil underground so removal is very difficult. All of this makes the Japanese Knotweed weed one of the UK’s most invasive non-native plants.

Removing Knotweed without having extensive knowledge, experience and using the right chemicals results in a high chance of it spreading to other parts of the soil which were previously unaffected and this is why Japanese Knotweed has such a reputation in the UK.

Where did Japanese Knotweed originate from?

Fallopia Japonica was originally brought back to the UK back in the middle of the 19th century by a German-born botanist named Philipp von Siebold. He found it growing on the side of a volcano and brought it to the UK to use as a beautiful ornamental plant in residential gardens. In around 1854 Siebold sent a shipment of various plants which included Japanese Knotweed to the Royal Botanic Gardens in Kew. The shipment was shared with the Royal Botanic Gardens in Edinburgh in 1854 and it was sold commercially by nurseries to homeowners and commercial properties and gardens and this is how it started to spread.

Where has Japanese knotweed been found in the UK?

Japanese knotweed is found all over the UK and is common in both urban and rural areas, In South Wales, there are high-density areas including Swansea and the surrounding areas.

How to identify Knotweed?

Japanese knotweed leaves can be identified by their shovel-shaped or heart-shaped leaves. They have a point at the tip and are staggered on the stem, with one stem per node which creates a zig-zag stem growth pattern. They are a bright and rich green colour and can grow up to 20cm long.

Japanese knotweed flowers are long clusters of creamy white flowers which appear towards the end of summer early September. The clusters can grow to around 0.5cm wide and up to 10cm long. The leaves remain as they are as the flowers grow which result in thick and dense foliage.

Japanese knotweed rhizomes are the part of the plant that grows extensively underground and they are known as its underground roots. The outside of the stem is dark brown and the inside is orange/yellow in colour. The fresh stems will be crisp like and will snap easily when bent. The rhizomes can grow up to 3 metres in-depth and up to 7 metres horizontally from the plant. This is the part of the weed that is most likely to make it spread and just one tiny fragment, as little as 0.7g can create a new knotweed plant.

Japanese knotweed stems can grow up to 2 – 3 metres tall, sometimes more and they are similar to Bamboo hence why it is often referred to as bamboo. They have nodes and purple speckles and the leaves grow outwards from the nodes in a zig-zag type pattern. As the weed matures the stems inside become hollow making them easy to snap in two and during the winter the stems become very brittle.

Japanese Knotweed is a perennial plant and its appearance changes with the seasons:

Japanese knotweed in Spring

Japanese knotweed grows fastest during the springtime and can reach 3 plus metres high. its new shoots emerge with a red/purple tinge and are often referred to as looking like asparagus spears. The leaves normally roll up and are dark green or tinged with red.

Japanese KnotweedJapanese Knotweed in Summer

By early summer, the plant is fully grown and reaches over 3 metres tall and by late summer clusters of creamy white flowers, will appear.

Japanese knotweed in Autumn

In Autumn the leaves start to turn yellow and will wilt, however, the density of its leaves remain. It can still be over 3 metres high and the hollow stems start to turn brown.

Japanese knotweed in Winter

At the beginning of winter, the knotweed canes will die off, it is still very much alive just isn’t actively growing. The leaves will change to a yellow colour, then into brown and fall off. The hollow canes become dark brown and brittle and they give way against each other, falling to the ground. In springtime, as the weed starts to actively grow again, you will see the previous year’s canes lying underneath the foliage.

How do you get rid of Knotweed?

Japanese Knotweed is almost impossible to control and remove yourself but a qualified NPTC person or company who has the experience and knowledge to use the right chemical substances can advise you of the best and most efficient way of removing it. Disposal is a problem as it is classed as “controlled waste” under the Environmental Protection Act 1990, and this means it has to be disposed of at a licensed landfill site at a cost which a Knotweed Specialist will have the qualifications to do.

What should you do if you find Knotweed?

If you find or think you have Japanese knotweed and you own the land it is your responsibility to control it, although you are not legally required to remove it. Removing or disposing of Japanese Knotweed without experience and knowledge will cause it to spread and this is the illegal point so it is vital that it is dealt with by a Knotweed NPCT qualified specialist who can advise you on the most effective way to control or remove it.

What is an NPCT (National Proficiency Tests Council) qualification?

City & Guilds NPTC, now City & Guilds Land Based Services is the UK’s largest awarding body in the land-based sector. It encompasses agriculture, horticulture, forestry, animal care, conservation, machinery and more.

What can I do if my neighbour has Knotweed?

There is no legal obligation to remove or treat knotweed as long as you are not encouraging or allowing it to grow onto any adjacent land (schedule 9 of the ‘Wildlife and Countryside Act 1981’ states, you must not plant or cause to grow Japanese Knotweed in the wild).

If Japanese Knotweed is allowed to spread onto your land then you can issue private nuisance proceedings in the Civil Courts for:

  1. damages for loss of enjoyment and diminution of value of a property
  2. the costs of removal
  3. an injunction against re-infestation

In addition to this, Local Authorities have the power to serve notice on an occupier of land which has Japanese Knotweed growing. The notice can require them to remedy any knotweed which could adversely affect the amenity of an area within a set period and failure to do this or failure to safely and properly dispose of the knotweed can lead to criminal liabilities.

Do I need to tell my mortgage company if I have Knotweed?

Yes, on your mortgage application you should tell them that the property you are looking to buy has Japanese Knotweed as it is known as an invasive plant that can cause damage to property and can take several years to eradicate.

Mortgage lenders are cautious with properties that are affected by Japanese Knotweed, however, it isn’t impossible to get a mortgage. Their main concern is that a property with knotweed could be at risk of damage posed by the plant (which is highly unlikely if the construction and foundations are sound) and the issues there will be when reselling the property.

A property seller is legally obligated to declare if knotweed is present on the land of the property they are selling.

Will Japanese Knotweed affect the price of my house?

Japanese Knotweed can affect your house price as people are very cautious due to its invasive growth and difficulty of completely removing as well as mortgage lenders being very cautious about lending money on a property with knotweed.

Do I need to tell the Council if I have Knotweed?

It is not an offence to have Japanese knotweed on your land and it is not a notifiable weed, however, under Section 14(1) and (2), of the Wildlife and Countryside Act 1981 it is a criminal offence to plant Japanese knotweed or otherwise cause it to grow in the wild or spread onto neighbouring land.

How quickly will Knotweed spread?

Japanese Knotweed can grow up to 20cm a day and in the height of its growing season its stem can reach up to 3, sometimes 4 metres high. Underground, the roots, rhizomes grow rapidly and can spread up to 7 metres horizontally and 3 metres deep.

How long does it take to get rid of Knotweed?

It can take anything up to 5 years to completely remove Japanese knotweed through specialist chemical treatments carried out by a Knotweed specialist, however, the time it takes to remove will depend on how big the area of knotweed is. Japanese Knotweed can be completely eradicated through excavation, where it is dug out of the ground by a Knotweed specialist and safely removed to prevent the risk of it spreading by one tiny fragment of crown or rhizome. This method is more commonly used when a development site has knotweed and the construction needs to start quickly.

Should I buy a property if it has Knotweed?

If the property you are looking to buy, or any adjacent properties or land has knotweed then you should be cautious about proceeding with your purchase. There is a burden and cost associated with Knotweed to control or remove it, as well as it impacting if you will be able to get a mortgage or resell the property further down the line. We would always advise that you request for a Japanese Knotweed Specialist company to come to the property you are looking to buy and assess and advise you on it. If you go ahead with your purchase then you will have a legal responsibility to make sure it doesn’t spread to your neighbours’ land.

Will diesel or bleach kill off Knotweed?

Bleach and diesel substances do not kill Japanese knotweed. They may kill the foliage above ground, however, they won’t kill the roots. Substances like this will pollute the ground, groundwater and be toxic to humans and any pets. A qualified and specialist Knotweed expert will use controlled and specialist chemical substances to remove knotweed.

Will burning Knotweed kill it off?

Burning knotweed will kill the stems above ground but it will not kill the roots which will continue to spread underground and subsequently grow above ground in its growing season.

What plants are often mistaken as Knotweed?

Plants that are often mistaken as Japanese Knotweed are:

  • Bamboo
  • Ground elder
  • Russian vine
  • Bindweed
  • Broadleaf dock
Are you able to concrete over Knotweed?

You can concrete over Japanese Knotweed and it won’t grow up through the concrete unless there are any gaps or joins, however, it will continue to grow and spread horizontally underneath the surface of the ground and it will find its way above ground when it can.

Can Knotweed damage my sewers or water pipes?

Japanese Knotweed can damage underground sewers, water pipes and drains. The knotweed’s the root system, the rhizome will find its way into the smallest hole on a pipe joint to find water and will spread quickly causing damage.

How dangerous is Knotweed?

Japanese knotweed is not poisonous to humans or animals but some reports claim it can irritate sensitive skin.

There are many myths that say you can remove Knotweed yourself, however, it is extremely difficult and there is a likelihood you will cause it to spread which is illegal.

You should always work with a Knotweed Specialist who has the experience and qualifications to control and remove it safely and successfully. Any specialist you use should be an NPTC qualified person or business who is trained to use the chemical substances needed and this is due to new legislation which covers the management, and removal of Knotweed.

There are lots of stories relating to Japanese Knotweed and the damage it can cause, however, it is just one of many plants in the UK that can cause problems to land, buildings and other structures. Other perennial plants can cause similar or worse damage to buildings and underground services and structures.

If you have or think you have Japanese Knotweed then contact us on 01269 591651 and one of our Knotweed experts will be able to answer any questions you may have or can arrange a property or land survey for you.

Green Leaf Remediation

Green Leaf Remediation Specialists covers the whole of South Wales (including Swansea, Cardiff and Newport), West Wales up to North Ceredigion & Powys and throughout South Glamorgan & Gwent & Tenby. We carry out contracts in the West Country, as far North as Shropshire and into the Midlands & Birmingham areas.

We are a fully qualified Japanese Knotweed Certificated Surveyor (JKCS) and we specialise in controlling Japanese Knotweed, other invasive plants and ‘general nuisance weeds’ which are found in the UK for residential and property development sites.

We also provide tree services, such as pollarding, crowning, pruning, felling, through our NPTC chainsaw operators, all of whom possess a vast amount of experience in the forestry industry.

Our Qualifications & Accreditations
  • City & Guilds NPTC Level 2
  • Principles of Safe Handling & Application of Pesticides (PA1/PA6)
  • Principles of Safe Handling & Application of Pesticides near water (PA6AW)
  • Herbicide Stem Injection
  • Property Care Association
  • The Control & Eradication of Japanese Knotweed Surveyor’s Training Course
  • Qualified Technician (PCAQT) in Japanese Knotweed
  • Accredited Surveyor in Japanese Knotweed