What Does Japanese Knotweed Look Like?

Japanese knotweed has shot up in popularity in recent years, not in purchases from garden centres but on internet searches by gardeners and home owners, lenders, estate agents and developers. First brought over from Japan by the Victorians, this incredibly hardy plant, naturally found on the slopes of volcanoes, has made itself right at home in the mild climate and fertile soils of Britain.

Unfortunately, despite all the conversation regarding this treacherous plant, it can still be difficult to tell someone what they should look out for if they suspect knotweed is growing on, or near, their property. So what does Japanese knotweed look like?

Japanese knotweed looks like a pretty harmless plant. A great clue to Japanese knotweed identification is that it has lime-green leaves shaped like playing card spades and its stems grow to two or three metres high in one season. However Japanese knotweed looks slightly different depending on the time of year.

  • In spring, this hardy perennial wakes up and sends its red asparagus-like shoots out to break through the soil. The shoots generally grow straight up. The leaves are still furled around the tip of the shoot which gives Japanese knotweed its ‘asparagus-like’ appearance.
  • In summer the supple young stems grow at a scary pace, turning bamboo-like and hardening in the process. The leaves, growing alternately along zig-zagging stems have opened up, revealing their classic spade shape and the knotweed can be seen in dense clumps called stands.
  • By late summer/autumn the plant is in full bloom, revealing a number of creamy-white flowers which turn to seed. Possibly the only knotweed-related blessing the UK has received is that only female plants grow in the wild, so none of the seeds are fertile. The alternative reality doesn’t bear thinking about! By now the canes have grown to 2 or 3 metres in height and tower above most other vegetation.
  • As winter turns, the leaves yellow and drop, leaving the canes brown, hollow and bare. Don’t be fooled - the Japanese knotweed may look dead but, in reality, it has simply gone into hibernation, ready for the day when spring arrives once more.

A point to note - if knotweed has been treated with herbicide or repeatedly pulled out / mowed while growing, it may display some very different growth characteristics. If you’re in any doubt, call the experts!

For effective Japanese knotweed identification, sending in good quality photographs to specialists like PBA Solutions is probably the simplest, quickest route. We will be able to tell you quickly if the plant you have snapped is knotweed and help you decide the best way forward from there.

Call PBA Solutions on 0203 174 2187 or email us at [email protected].