Japanese Knotweed

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Where did it come from?
Originally native to Korea, China and Japan; once introduced into Europe, in the 19th century,  as an award winning ornamental plant, Japanese Knotweed (Fallopia japonica) has been very “successful” in spreading quickly to cover large areas; particularly canals, railway sidings and levees. It was bought by the rich in the 19th century due to its exclusivity. However now it’s known as “The Plant that ate Britain”; not so exclusive nowadays!
What’s the problem with Japanese knotweed?
Stems can emerge through concrete and tarmac with apparent ease which highlights the serious damage it can do to buildings. The plant is adaptable; tolerating various types of soils and appears to have a high tolerance for acidity, alkalinity and salinity and due to a lack of predators here in the west, it can spread without the risk of being eaten/killed by natural sources.  In short, it grows just about anywhere and this is why now Japanese Knotweed is such a problem for home owners and buyers especially when cases of it have devalued properties by up to 40%!

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JAPANESE KNOTWEED (Fallopia japonica)

Japanese knotweed is classified as a non-native, invasive species in the UK and can cause serious damage to brickwork, concrete, drains and buildings. Laws have been created in the UK specifically for Japanese knotweed and other non-native, invasive species and you can learn more by visiting The Law page.

Japanese Knotweed (Fallopia japonica) can have many forms of size, from 1 small stand a few inches high, to a 1000 stands at 6ft high, all in one cluster or spread over a mass area. The best thing for anyone to do when tackling the problem is to have a professional survey conducted ASAP on the areas suspected to be infested to assess the weed and any dangers it might be posing to close by buildings, roads etc.

Characteristics:

· Hollow stem with a bamboo like appearance.
· Leaves grow in a distinctive zig-zag pattern.
· The plant can grow to heights of 3-4 metres.
· Leaves are a heart/spade type shape, have a smooth thick cuticle like skin with a mid-green colouring.
· Leaves grow up to around 12cm long.

Japanese knotweed plants are female with sterile seeds therefore spreads by developing a large network of rhizome which spreads meters in length, travelling underground at an alarming speed and appearing up to distances of 6-7 metres away from the originating spot.

OTHER KNOTWEED SPECIES

IDENTIFYING THE DIFFERENT TYPES OF KNOTWEED:

In the spring you may see buds appearing like red coloured asparagus tips. They will grow in to stands that look like bamboo shoots with red leaves which grow in to green leaves with red veins and finally fully green leaves in the summer.

The weed produces chains of white flowers/seeds in the summer making the appearance of Japanese Knotweed quite attractive therefore misleading many home owners to its very real dangers.

In late autumn and early winter you will see the plant dying, preparing for hibernation. Leaves will dry out and drop off while stems will dry out and turn a brown colour leaving a very unattractive sight – sort of like a bamboo cane.

GIANT KNOTWEED (Fallopia sachalinensis)

Giant Knotweed (Fallopia sachalinensis)

Giant Knotweed
  • Hollow stem with a bamboo like appearance.
  • Leaves grow in a distinctive zig-zag pattern.
  • The plant can grow to heights of 4-5 metres.
  • Leaves are pointed at the tip, crinkly in appearance and have long white hairs on the underside.
  • Leaves are much more elongated and can grow up to around 40cm.
  • The growth span is shorter than JK at around 6 months from Mid/Late Spring.
  • It will flower in late summer with creamy/white flowers.

KNOTWEED HYBRID (Fallopia x bohemica)

KNOTWEED HYBRID (Fallopia x bohemica)

Japanese Knotweed Hybrid
  • Hybrid formed of Japanese knotweed and Giant knotweed.
  • Hollow stem with a bamboo like appearance.
  • The plant can grow to heights of 2.5-3.5 metres.
  • Leaves are a heart/spade shape and pointed at the tip, crinkly in appearance and have short white hairs on the underside early in the year.
  • Leaves are dark green and can grow up to around 25cm.
  • It will flower in late summer with creamy/white flowers.

HIMALYAN KNOTWEED (Persicaria wallichii)

HIMALYAN KNOTWEED (Persicaria wallichii)

  • Hollow stem with a bamboo like appearance
  • Leaves are slender and elongated and grow in the distinctive zig-zag pattern.
  • Hairy stems and brown sheaths at the base of leaf stalks.
  • Leaves are darker green, can be heart shaped and pointed, leathery and grow to a length from 10cm to 20cm.
  • Short hairs often grow on the underside and edges of the leaf.
  • It will flower in late summer/early autumn with white/light pink flowers.

DWARF KNOTWEED (Fallopia japonica var. Compacta)

DWARF KNOTWEED (Fallopia japonica var. Compacta)

  • Dwarfed species of Japanese knotweed.
  • Hollow stem with a bamboo like appearance.
  • Leaves are of a variable shape and grow in a distinctive zig-zag pattern.
  • The plant can grow to heights of 1-2 metres.
  • Leaves are crinkled, often curled and have a thick cuticle like skin with a dark green colouring.
  • Leaves grow up to around 11cm long.
  • In late summer clusters of white/light pink flowers will bloom.

LESSER KNOTWEED (Persicaria campanulata)

LESSER KNOTWEED (Persicaria campanulata)

  • Leaves grow in an alternate pattern, not zig-zag.
  • The plant can grow to heights of 1 metre.
  • Leaves are grooved like those of a herring-bone, can be red in colour and have small white hairs on the underside.
  • Leaves are still elongated but size varies.
  • It will flower from summer until late autumn with very small, bell shaped, white/light pink flowers.