What is Japanese Knotweed?

What is Japanese Knotweed?

Japanese knotweed is the UK’s Number One non-native invasive weed species with Giant Hogweed and Himalayan Balsam following up close behind. The most common form of this alien invasive species, Fallopia Japonica, originates from Japan where native predators effectively control the spread of this plant. Unfortunately this is not the case in the UK and Europe.

Japanese knotweed problems and effects

The problem with Japanese knotweed is that it rapidly spreads, contaminating a vast land mass causing damage to surface and structures, particularly those which have weaknesses that Japanese knotweed can exploit. 

As a non-native invasive weed it threatens bio-diversity by outcompeting native plant species and can penetrate anything from roads, walls and floors. Japanese Knotweed has an incredibly robust root system which means that it is especially hard to get rid of; a root fragment (rhizome) smaller than a penny is enough to rejuvenate it and cause continual damage.

Find out how to control Japanese knotweed here.

About Japanese Knotweed

The Victorians were responsible for its introduction; they often loved Japanese knotweed as an attractive Dogwood like shrub!  Today conservationists argue that Japanese knotweed is a particular benefit in urban areas as it provides nectar to bees and butterflies when flowering in late August.

Japanese Knotweed has the following external characteristics:

  • It forms dense clumps known as ‘stands’.
  • The hollow stems look like bamboo while the shield-shaped leaves look similar to dogwood
  • In the spring the plant produces fleshy red tinged shoots, quickly developing into dense stands as described above
  • These stands can reach a height of 1.5 metres by May and 3 metres by June.
  • Typical locations to find knotweed: common along railways, riverbanks, roads, footpaths and derelict sites. It often grows in an area after being dropped, dumped or fly-tipped in soil or garden waste.

The root system:

  • Japanese knotweed has an extensive underground root (rhizome) network.
  • Knotweed normally extends to approximately 3 metres from a visible stand but has the potential to spread to 7 metres where ground conditions allow.
  • Roots can reproduce through vegetative propagation, meaning that new plants can be created from small fragments of existing plants. A fragment of root as small as 0.7 grams can grow to form a new plant.

Did You Know?

According to the Wildlife and Countryside Act 1981 it is a criminal offence to “plant or otherwise cause” the growth of Japanese Knotweed in the wild. Find out more about Japanese Knotweed and the Law.

Like many plants, Japanese knotweed is seasonal and looks different at different times of the year. If you think you have Japanese Knotweed growing on your property, send us a photo or organise a free site survey. Don’t attempt to deal with it yourself as cutting or trimming will encourage its spread.

PBA Knotweed Solutions is an accredited and Trustmark approved Japanese Knotweed specialist and founding member of the Property Care Association. As an insurance-backed invasive weed company, we have over 18 years of experience in the field of invasive weed management and eradication. To find out more about how we can help you with Japanese knotweed problems, give us a call on 0203 174 2187.