Identifying Japanese Knotweed


What is it?

Fallopia japonica – commonly referred to as Japanese Knotweed, is a plant species originally only found in East Asia. It was brought to the UK in the mid-1800’s, where it was favoured by gardeners due to its similarities to bamboo and the fact that it could grow anywhere. It has since spread throughout the UK, often being found on wasteland, alongside roads and on riverbanks. If you’re unfortunate enough, you may have also discovered it on your own property.


Why does it carry such a bad reputation?

A root system (rhizome) that can extend up to 7m from the plant and travel 3m deep makes Japanese Knotweed extremely difficult to eradicate. Once fully established, it can reach up to 3m in height, and while sprouting can grow at a rate of 2cm per day, meaning it often out-competes the UK and Ireland’s native plant species and becomes the dominant plant in the area. It has the ability to damage foundations and structures (tarmac, concrete, etc.), meaning mortgage applications are often declined if the plant is found on or near the property.

Japanese Knotweed is classed as one of the most invasive plant species in the UK and Ireland and is strictly regulated by both the British and Irish governments.


What does it look like?

Japanese Knotweed has a life-cycle and changes appearance depending on the time of year. Here’s some advice on how to spot it through the seasons.


Japanese Knotweed spring plant stage

  • Extremely fast growth (up to 20cm per day)
  • Shoots appear a reddish purple in colour but may also be green
  • Can look similar to asparagus in this stage of growth
  • Rolled up leaves either red or green in colour

Early Summer

Mature Japanese Knotweed in the summer

  • Characterised by its green spade or heart shaped leaves
  • Can be up to 3m tall
  • Stems are hollow and are easily broken
  • Leaves shoot from stems intermediately, forming a zig-zag pattern

Late Summer

Japanese Knotweed Summer Flowers

  • Creamy white flowers bloom in late summer (August/September)
  • The flowers are in clusters up to 10cm in length
  • Individual flowers are around 0.5cm in size


Japanese Knotweed in Autumn

  • In autumn the foliage will begin to wilt and turn yellow, progressing to brown and then falling from the plant


Japanese Knotweed in the Winter

  • All that remains of the Japanese Knotweed are dead canes
  • The canes can often remain well into the following season
  • The Japanese Knotweed will sprout again in early spring due to its roots (rhizomes) still being active beneath the soil.

Getting Rid of Japanese Knotweed

If you have a small infestation of Knotweed it may be possible to treat yourself using a glyphosate-based weedkiller. Using a weedkiller will involve cutting the knotweed and injecting directly into its stems as to penetrate the rhizome system below the soil. Depending on how established the plant is, this method can take up to 5 years, although it can take up to 10 years depending on the strength of the weedkiller.

ATG Group are specialists in eradicating invasive plant species. We have many options available depending on clients budgets and timelines. We have successfully completed many major Japanese Knotweed eradication contracts in the commercial and public sector, as well as smaller domestic jobs (see our range of case studies for more).

If you’re concerned about Japanese Knotweed on your property, a neighbouring property, or have identified it on your site, get in touch for expert advice. We can provide you with a range of options to deal with any size of Japanese Knotweed problem, all backed by warranty.