At SE Knotweed, we identify Japanese knotweed by season: pink and red asparagus-like shoots in spring, fast green growth and creamy flowers through summer, yellowing dieback in autumn, and hollow brown canes standing through winter.
In spring, from around March, Japanese knotweed sends up pink or red shoots that resemble asparagus spears, tightly rolled and pushing through the soil where last year's canes stand. They unfurl quickly into green, red-speckled stems with heart-shaped young leaves.
Spring is the point to act, because a stand caught early is smaller and cheaper to treat or remove, and stem-injection treatment begins once the canes are established.
By summer the stand is at full height, 2 to 3 metres of hollow bamboo-like cane carrying bright green shovel-shaped leaves in a clear zig-zag. From late July into September it produces sprays of small creamy-white flowers that attract bees.
Summer is when knotweed is most obvious and most often reported, and it is the main window for the herbicide programme because the plant is actively drawing herbicide down to the rhizome.
In autumn the leaves yellow and fall and the canes begin to die back, though a late-season stand can still be flowering into October. The plant is drawing its reserves down into the rhizome for winter, which is why a final autumn herbicide treatment is effective.
The fading foliage can make a stand harder to spot, so an autumn find is worth confirming before growth restarts in spring.
Through winter Japanese knotweed stands as clumps of hollow, brittle brown canes, often knee to head height, with no leaves. It looks dead, but the rhizome below ground is alive and dormant.
The dead canes are a reliable winter marker, and finding them is a good reason to arrange a survey before the spring shoots and the buying season arrive together.
Late spring to early autumn, roughly May to September, is easiest, because the canes, the zig-zag leaves and the creamy flowers are all present together and hardest to confuse with anything else.
Whatever the season, if you are unsure, our identification guide shows the core signs and we can confirm from a photograph.
Tell us the address and what a surveyor flagged. We confirm the plant, record the RICS category and set out the figures.