How quickly do Japanese knotweed roots spread?   Japanese knotweed is the fastest-growing plant in the UK.  The weed’s roots can create an invasive and destructive network that can damage building foundations, and water systems, and damage other plants in the ecosystem.

Japanese Knotweed roots are found in many places, but they can be a problem when they grow near foundations or other structures. This blog post will explore how the Japanese knotweed spreads and what you can do about it.

The plant produces large amounts of seeds which travel through waterways and disperse on land to form new plants. It also reproduces by sending out rhizomes underground that each produce their own set of rootlets with time making them difficult to control once established.

This article will discuss the various means by which this weed is spread and how best to avoid it happening.

How are the Japanese knotweed roots spread?

The Japanese knotweed produces seeds from its flowers. However, it is unlikely that the seeds will germinate because of their female nature.  The only options remaining for the plant to disperse include; rhizome, crown and stem cuttings.  Here is how the plant spread through some of its parts:

Stem:  The knotweed can regrow from nodes of the green stem in water or soil.

Crown: The crown can survive harsh climatic conditions and easily produces new plants when left in soil or water.

Rhizomes: The rhizome is an underground stem that easily grows into a new plant. The Japanese knotweed roots weigh less than 0.7 grams but can grow so fast up to 3 meters deep and 7 meters horizontally.

The fragmenting of the rhizome facilitates the growth of small red buds hence new plants. This is why you should never accept soil transfer to your property without proper inspection.

Old buildings are vulnerable overtime as Japanese knotweed roots will damage them structurally
Old buildings are vulnerable overtime as Japanese knotweed roots will damage them structurally

What conditions are needed for the Japanese knotweed roots to spread?

The Japanese knotweed is the most invasive weed in the UK because of its ability to grow anywhere. It grows in both poor and good soil. It quickly overshadows any plant that grows beneath it due to its strong root system.

It becomes out of tiny cuttings spread by water and humans, as told above. This knotweed does not need much to survive.

Can Japanese knotweed spread on shoes?

The Japanese knotweed can only spread through rhizomes in the UK. Shoes can easily cover a tiny piece of the rhizome. The root easily gets stuck on the sole of your shoes; this means that you can easily and unknowingly transport it to another area where it can grow and spread fast.

Remember that this plant is extremely invasive, and it should be handled with a lot of care to minimize the spread.

Waterways suffer from this invasive weed and change our landscape dramatically
Waterways suffer from this invasive weed and change our landscape dramatically

Why should you not let the Japanese knotweed roots spread?

Why are Japanese knotweed roots considered such a problem?

Food and water risk: The dense knotweed foliage causes heavy shading of small river sources, reducing and affecting aquatic life. The knotweed also makes it harder for water to carry floodwater.

Sports: Japanese knotweed highly hinders boaters and other sportspersons from enjoying their everyday life. It also makes it harder for one to have better views downstream or even to dock your boat.

Infrastructure: The knotweed is invasive and easily grows through the cracks of the house, walls, and water drainages. This causes massive damage to the already existing infrastructure. A lot of money goes into the reconstruction of such properties and treatment of this weed.

Safety: The weed can obscure railways and road signals, which is hazardous to users in order to avoid hazards.

Property devaluation: Knotweed has a huge impact on properties in the UK. A good number of mortgage providers are turning down applicants who have properties with this plant on them. Especially if no action has been taken, seek professional advice to avoid devaluing your property.

Bio-diversity: The knotweed largely affects ecosystems by dominating native plants, thus limiting their adversity.  Research has shown that the plant releases harmful chemicals that can easily kill other existing plants around it.

Flowers blossom in late summer and dominate the locality
Flowers blossom in late summer and dominate the locality

Can birds or animals spread Japanese knotweed in their droppings?

There is a possibility that animals and birds can spread the knotweed through their droppings. Animals such as goats feed on the shoot of the knotweed, which is indigestible. The shoots once excreted begin to grow.

Birds can transport the knotweed fragments through their fur. It is common to see birds and some animals walk through contaminated soils. The particles can be easily carried by their beaks or fur to new areas where the pieces start to grow.

Also, Japanese knotweed roots are exposed above the ground and any animal including birds can easily transfer the fragments of these roots to the local area and just a small fragment can begin the growing process all over again.

New shoots grow aggressively and close together and at such a rate to dominate all other species of plants
New shoots grow aggressively and close together and at such a rate to dominate all other species of plants

How far can Japanese knotweed roots spread?

Japanese knotweed can spread far and wide in favourable conditions. The plant grows naturally up to 3 meters deep and 7 meters horizontally. The plants grow up to 10 cm each day during summer. It grows so fast when there is minimal or no disturbance of the ground. 

Japanese knotweed easily spreads into your neighbour's property
Japanese knotweed easily spreads into your neighbour’s property

Is Japanese knotweed a notifiable plant?

It is the responsibility of property owners to control the knotweed spread.  It is against the law to allow the plant to spread into your neighbour’s properties or neighbouring public land. While the plant is extremely invasive, no rules require you to report its presence to the authorities.

It is an offence to dispose of this weed carelessly in the wild.  It is a public crime that can lead to heavy fines. Anyone can open a legal action; it is only good to stay out of trouble by taking the necessary and recommended actions once you come across a plant growing on your property or near you.

What starts as one small section can become an infestation in a matter of years
What starts as one small section can become an infestation in a matter of years

What should I do to stop the Japanese spread?

If you come across the weed growing on your property or anywhere else near you, you can call local authorities. It would be best if you didn’t cut any stems or flowers as the real problem is the Japanese knotweed roots system. The unseen is where the danger lies.

Knotweed removal experts are best in identification and treatments, thus proper eradication is advisable. It is quite challenging to get rid of this plant; all the above-ground parts should be controlled regularly for several seasons to kill each piece.

Digging or cutting down the weed has no significance when it comes to its control due to its main spread being underground.

Final thoughts

A single root can produce a dense field of the weed, as it’s able to grow anywhere that sunlight reaches. This makes it very difficult for any other plant life or vegetation to thrive in an area with heavy infestations.

Most notably, the roots are spread by rhizomes, which can grow up to three inches a day in moist soil conditions.

They reproduce even more rapidly when new stems emerge from them during each season’s growth period as seen often on steep banksides of rivers with heavy rains or flooding–which is just one environment that makes this invasive weed so dangerous for both humans and animals alike

Want to know more?

Knotweed Removal aims to provide the most up-to-date information, help and advice for YOU to make informed decisions. If you are unsure or uncertain about how to proceed, please reach out to us and we will gladly come back and advise you as best we can.

Governmental advice can be found here and the UK law covering the removal of Japanese Knotweed as stated under the Wildlife and Countryside Act 1981 can be found here.

The best means to contact us is via our email –

Do not forget we have a library of blogs covering many areas relevant to Japanese Knotweed, our free downloadable How-to Guides and Product Reviews on the latest methods being employed to eradicate or remove Japanese Knotweed.

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