Japanese knotweed looks different throughout the year.
In order to correctly recognise Japanese knotweed it’s useful to have a reference point to better understand the various stages of this elusive plant’s life cycle.
In this guide we’ll take you through how to identify Japanese knotweed throughout the seasons. If you’ve spotted this plant on your land in any of these forms then get in touch with us (using the contact form to the right) so we can help to positively identify it and move forward with a plan.
Japanese knotweed enters several recognisable phases throughout the year, whilst treatment can take place at any time it’s typically easier to spot during the Summer as this is when the plant is most visible above ground. Knotweed often appears to ‘die back’ during the colder months, but it’s unwise to assume that your problem is simply gone. Whilst the plant enters this dormant phase above ground it is still alive and kicking under ground.
Root systems (known as rhizomes) can burrow up to 3 metres deep into the ground with individual rhizomes growing up to 20cm thick, but this kind of growth only occurs if the plant is given the time and space to flourish. Rhizomes are dark brown on the outside and orange on the inside, you can usually break them in your hands unless they have grown into a larger clump or ‘crown’. You might well bump into a network of roots whilst you’re digging in the garden or landscaping. If you do it’s imperative that you do not distribute any of the plant matter as these rhizomes can propagate more plants from just the smallest of fragments.
Early Spring: February-March
The sooner you tackle your infestation the quicker you’ll be able to get rid of it for good, but the plant can be difficult to spot until major growth above the surface begins to take place. In early spring you might see buds appear at the base of old stems. Keep an eye out for any red/pink tips pushing through the ground, these buds grow to be around 1-3cm wide and will soon be replaced by easier to spot shoots.
Once spring is under way Japanese knotweed shoots become a lot easier to spot. Pinkish red buds soon give way to more recognisable spear-shaped shoots, which are sometimes described as ‘asparagus like’. At this stage leaves are red and rolled up, but they soon turn green as the plant grows skyward.
Growth accelerates significantly during summer making the plant much more conspicuous. The hollow stems grow up to 2cm a day and the leaves now assume their most recognisable shield shape with an alternating stem pattern. This presents a good opportunity to treat the problem with a PCA-accredited glyphosate programme, professionals are able to assess your infestation and inject each plant with their specialist equipment.
Be warned that there are a variety of sub-species and cross-breeds that can easily be confused with this plant, send us photos of your potential infestations to get a positive ID before looking in to how to eradicate your knotweed problem.
By mid-summer knotweed plants are close to reaching their full height (between 1.9-3m). The stems are now less green and are rigid with more pronounced dark purple speckles. Clear nodes are visible on these stems giving them the appearance of bamboo, they can also be snapped easily in the hand.
Late Summer: Knotweed Flowers
It’s not until late summer that Japanese knotweed flowers; multiple bunches of creamy white flowers appear amidst the leaves, but the seeds that are produced from this process rarely lead to new growths.
Autumn to Winter: September-February
As Autumn progresses, stems redden and the plant sheds seed cases. If the weed is left to its own devices the leaves and flowers will eventually begin to fade and fall back. In the middle of winter all that remains above ground is a collection of pale, dry canes with the rhizomes lying dormant beneath the surface waiting for warm weather to sprout and spread further.
We could help you recover the costs of treating your knotweed problem, especially if you’ve been sold the land without knowledge of the plant or if it has entered your property from a neighbouring property.
If you have any plant matter on your land that resembles these images then it’s worth taking your own photo and sending us your images using the form on the right. Write us a message, chat with us using the button on the bottom right, or give us a call on 0151 242 9050.