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Japanese Knotweed Identification

Identification through the seasons


In spring, red/purple asparagus like shoots appear from the ground and grow rapidly forming canes.  As the canes grow the leaves gradually unfurl and turn green. One of the tricks of Japanese Knotweed is how fast is actually grows in the early stages of spring. Very quickly, Japanese Knotweed stems can grow from small shoots to 10 feet (3 metres) in height. When it comes to Japanese Knotweed identification in spring, over a few weeks, the growth can look very different.


In summer, the plants are fully grown and mature canes are hollow with a distinctive purple speckle and form dense stands up to 3 metres high. The density of the plant can be seen at this stage making Japanese Knotweed identification in summer very easy. In late summer, the full bloom of the plant is actually very attractive with small white flowers.


In Autumn, Japanese Knotweed has a lot of similar identification traits as to that of summer. In the beginning of autumn, there will certainly still be a very good density of foliage on the plants. The leaves will begin to turn yellow in colour with a distinctive mix of green and yellow leaves within the foliage; the leaves will also begin to wilt.


In Winter, the flowers and the green of the leaves of Japanese Knotweed will die off, all that will remain are the bamboo type canes that will turn darkish red/brown, and die. The canes remain standing throughout the winter and can often still be seen in new stands in the following spring and summer.

Key Identification Features of Knotweed

Negative Economic Impacts of Japanese Knotweed

  • Damage to property
    Japanese Knotweed can grow through tarmac, concrete, brick walls and foundations – putting your property at risk.
  • Mortgage refusal
    Should you have any Japanese Knotweed on your property and are looking to sell – potential buyers may not be able to get a mortgage to purchase.
  • Planning permission
    Planning may have conditions attached which can impact on loan approval.
  • Land Price
    The price of your land or property may be greatly affected if it is proven that you have Japanese Knotweed.
  • Neighbouring Land
    If you have Japanese Knotweed spreading onto your neighbour’s property and cannot come to an amicable solution, you could be liable to have legal proceeding taken against you.
  • Aggressive growth
    If you don’t control it, it will soon control you – Japanese Knotweed can spread from a single piece of its stem and grow up to 4 inches per day.
  • Impact on the Environment
    Because of the vigorous growth of the Japanese Knotweed, it outcompetes all other native plants not allowing them to grow.
  • Legal responsibilities
    Under the Wildlife and Countryside Act it is illegal to “plant or cause to grow” Japanese Knotweed in the wild.

Should you suspect the presence of any invasive plant on your property, we strongly recommend that for clarification purposes you contact us and a certified surveyor from the Japanese Knotweed Company will carry out a site survey.

The cost of ignoring your Japanese Knotweed problem for any length of time could be high, remember a small Japanese Knotweed plant can quickly become a major infestation.


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