How to Identify Japanese Knotweed

Leaves:
Japanese Knotweed

  • New leaves are dark red and 1 to 4cm long.
  • Young leaves are green and rolled back with dark red veins.
  • The mature leaves are green and heart-shaped but flattened at the base, and usually around 12cm long.


The flowers:knotweed flowers

  • They bloom in late summer
  • They are creamy white in colour and 0.5cm wide
  • They form clustered ‘spikes’ of flowers amongst the foliage
  • Spike lengths are approximately 10cm

 

Rhizome (root)Rhizome

  • Sections can be from a few mm to 20cm in diameter
  • The exterior is dark brown and the inside is orange/yellow
  • They are easy to snap (like a carrot)

 

Crown Buds

  • They form in early spring
  • They are round in shape at the base of old stems and are 1-3cm wide
  • They are pink/red in colourv

 

Stem

  • New stems grow annually and develop from the crown buds

In Spring

  • New shoots are fleshy
  • They are dark red/green in colourv

In Summer

  • They grow to a maximum height of 2-3m
  • They are green with red/purple speckles
  • They are hollow
  • The leaves form an alternate zig-zag pattern along the stemsv
  • The crowns that the stems emerge from forms dense clumps

In WinterWinter Knotweed

  • The leaves fall and the shoots die back to leave dead, light brown hollow stalks (a bit like bamboo).

The best time to spot Japanese knotweed is during mid-summer and early autumn. During spring reddish/purple shoots appear from the ground. These can grow up to 2cms a day, thus rapidly forming into bamboo-like stems that develop green heart- or shield-shaped leaves.

By early summer the mature Japanese knotweed stems are hollow with purple speckles and can reach up to 3 meters in height. The leaf growth alternates on each side of the stem producing an obvious knotweed zigzag pattern.

The flowers that emerge by late summer are creamy-white in colour, and in lengthy cluster formations. Japanese knotweed spreads by its underground roots which lie dormant, but alive, over the winter months. Knotweed rhizomes (roots) can spread 7 meters outward and 3 meters deep.

Hybrids

Japanese knotweed (Fallopia japonica) can also hybridize with its related species. The most common of these hybrids is that of Japanese knotweed and giant knotweed (Fallopia x bohemica). The hybrid knotweed then has the ability to spread by seed, which Japanese knotweed was lacking before due to the absence of any male plants in the United Kingdom.

 

Giant KnotweedGiant knotweed (Fallopia sachalinensis) is native to the island of Sakahlin which is just north of Japan but part of Russia. However, similarly to Japanese knotweed it was brought to Europe to be grown in botanical gardens. It has also spread to the wild and acts as an invasive species. It is similar to Japanese knotweed in many respects but is larger, growing over 4m high and having leaves around 20-40cm. Giant knotweed also has flowers that are greener in colour and leaves that are more rounded at the base than Japanese knotweed with scattered hairs on the undersides.

The hybrid plant (Fallopia x bohemica) grows slightly larger than Japanese knotweed and has slightly larger leaves but is smaller than giant knotweed. The leaves also have a pointed tip and a slightly rounded base with short hairs on the underside, which distinguish it from its Japanese knotweed parent.

 Japanese Knotweed Identification Card




Our Clients

Click here to view a small selection of clients we have worked with past & present.
Go

Testimonials

Find out what our clients think about our services.
Go

Case Studies

View information on a selection of our case studies.
Go

Contact Us - Head Office
t: +44 (0) 1273 7044 49
f: +44 (0) 1273 7044 99
e:
Go