How to Identify Japanese Knotweed

Japanese knotweed is an interesting, though destructive, plant. With origins on the slopes of Japanese volcanoes, it is one of the most resilient weeds present in the UK today.

It will grow through cracks in concrete and building foundations, corrupting the structural integrity of buildings and infest huge volumes of the soil in your garden, so if you think you may have knotweed growing on your property it’s best to get it surveyed by an expert to carry out a Japanese knotweed identification. Book your  site survey with PBA Solutions today.

Japanese knotweed is a perennial plant, which means that it puts out new shoots each year from its rhizome (stem and root system). It grows quickly in the spring and summer and goes into hibernation for the winter. In the autumn it stores vast quantities of nutrients in its extensive root system so that, come summer again, it can come back with full force over a greater surface area.

Because its defining features change through the seasons, Japanese knotweed identification can be tricky. It is most identifiable by its spade-shaped leaves (like the playing card spades).


Japanese Knotweed in spring

How to identify Japanese knotweed in spring

Japanese knotweed in spring sends up new shoots which may be speckled with red and purple. Furled leaves develop at the tip, making the shoots look like asparagus spears. As the season progresses it moves out of the ‘purple shoot’ stage and the shoots literally shoot upwards, by as much as 30 cm (one foot) a week. Knotweed will develop dense clumps of growth known as ‘stands’ with green canes speckled with purple hues and lime-green leaves, now unfurled growing alternately from the stems.


How to identify Japanese knotweed in summer

Japanese knotweed not only grows incredibly fast but can also reach heights of over 2.5 metres. Large stands will be pretty impressive then, covering large areas and swamping many other plants. Japanese knotweed also exhibits a pretty sprays of creamy white flowers at the height of its growth period. Sometimes confused with bamboo, bindweed dogwood and lilac, it’s always good to get a professional opinion.


How to identify Japanese knotweed in autumn

In autumn, Japanese knotweed seems to take a breather, as its growth slows and stops. 

The flowers will go to seed (not viable seeds thankfully!) and the leaves will turn yellow, wilt and fall, exposing the bamboo-like canes. The once-green canes will also turn colour towards dark brown or red. During this time, however, the knotweed has taken in huge quantities of nutrients, storing as much food as possible for the following year.


How to Identify Japanese Knotweed in winter

Japanese knotweed in winter can looks like a clump of dead bamboo canes. The canes are now dead, hollow and brown having played their part in storing the energy gained in the summer below ground in its root system. Although it looks dead, Japanese knotweed is just biding its time until the weather warms up, so if you think a cold-snap has killed off your knotweed infestation, think again!


Call PBA Solutions for effective Japanese knotweed identification and treatment packages with a near 100% success rate. Pick up the phone to talk to a member of our team on 0203 174 2187 or email us at [email protected].