How to Identify Japanese knotweed

Japanese knotweed identification is worth understanding if you are a homeowner, landowner or developer, as it could make the difference between successfully ridding yourself of a potential costly curse at an early stage, or presenting you with a problem that can be difficult and costly to eradicate once it has become firmly established. Learning how to identify Japanese knotweed can be tricky – it is a case of understanding what to look for, and which parts of Japanese knotweed stand out at different times of the year. 

There are some key components to understand in order to be effective with Japanese knotweed identification. For instance, there are different ways to identify Japanese knotweed depending on the seasons; failure to realise this can mean missing key parts of the plant’s growing process and therefore not realising there is a problem until it is too late. 

It is also important to note that there are also other types of knotweed that might be on your property. By being more aware of the various stages of Japanese knotweed growth will help when it comes to correctly identifying knotweed and then deciding about your next course of action.

What is Japanese Knotweed?  

Japanese knotweed is a type of knotweed that is prolific in terms of rate of growth, but thankfully there are distinctive identifiers which alert people to the fact that there may be a problem to deal with. You can identify Japanese knotweed by the growth pattern of one stem per node, creating a stem growth pattern that is zig-zag in nature.  

The leaves are smooth, a mid-green colour, and have a straight back edge leading them to resemble a shield shape. The flowers on Japanese knotweed are small in size and are a cream (off-white) colour, and form in little clusters that are loosely located. These flowers bloom in late summer and during the early part of autumn.  

Understanding the different features of the Japanese knotweed through the seasons is an important part of identification. Early identification allows effective control at a much earlier stage, thus reducing potential damage and costs. 

How can you identify Japanese knotweed at different times of the year?

Japanese knotweed identification becomes much easier when you are aware what the plant looks like at various stages throughout the year. Japanese knotweed grows in the spring, with new shoots emerging in red and purple colours that closely resemble the spears of an asparagus. The leaves will be rolled up and dark green or red. 

During the summer months the leaves begin to change into the shield shape and can be up to 15cm long. It is during late summer and early autumn when the white flowers begin to bloom, and the stems are mostly hollow and form in the zig-zag shape mentioned. 

As we move into the autumn the leaves remain in place but will begin to change colour into yellow, and the stems will turn brown. The plants can still reach 2-3 metres in height during this period.  

Winter is the time when knotweed canes begin to die, and the weed becomes dormant in nature. The leaves will go from yellow to brown, and eventually fall off, whilst the canes are so hollow that they can collapse.  

What part of Japanese knotweed is the main risk?

The rhizomes of Japanese knotweed are the underground stems which can cause damage and are most worrisome for property owners. They can snap quite easily when fresh, and appear dark brown on the outside and orange in the centre.  

The underground roots of Japanese knotweed can grow to depth of around 3 metres and can extend away from the plant at a distance of up to 7 metres. This is the part of Japanese knotweed that is most troublesome, as new plants can grow from a small piece of rhizome, as small as your finger nail. 

Learning how to identify Japanese knotweed is important as it can help you to start to tackle the problem early on and hopefully avoid the structural problems that many Japanese knotweed-infested properties can face. Correct Japanese knotweed identification is best confirmed by a professional Japanese knotweed removal company who can then advice you on the next steps.  

Use a company like JKSL that you can trust to deliver a comprehensive Japanese knotweed removal service before the problems become overly large. This can help avoid damage to your property, and any potential lawsuits should the knotweed on your land spread to any neighbouring properties.