Knotweed through the year: what it looks like in every season
A month-by-month visual guide so you can spot it in March as easily as in August.
Knotweed changes appearance dramatically through the year. Most homeowners only learn what it looks like at the height of summer, and then miss it entirely in spring or winter. Here is what to look for in every season.
Late winter (Feb – early March)
Tall, hollow, straw-coloured dead canes from last summer, often still standing in clusters. Brittle, light, easy to snap. The crown at ground level is a knot of woody material with no visible green growth.
Spring (mid-March – May)
The most distinctive stage. Fat red-purple shoots emerge from the crown like asparagus spears, growing 2 to 4 cm a day. By late April they are 50 cm tall, with leaves unfurling and the characteristic zig-zag becoming obvious.
Early summer (June – July)
Full green growth, shoulder height, dense and shading out everything around it. Stems show clear purple speckling. This is the easiest stage to identify and the worst to ignore.
Late summer (Aug – mid-Sept)
Creamy-white tassel flowers appear in the upper leaf joints. The plant is at full size and we are usually mid-way through the second herbicide application of the season.
Autumn (late Sept – Oct)
Leaves yellow and drop. Stems begin to dry and turn brown. The site looks tatty and unloved, but the rhizome is still very much alive and pulling resources down for the winter.
Winter (Nov – Jan)
Bare standing canes, no leaves, no flowers. Easy to walk past without noticing. This is in fact a great time to commission a survey and have a treatment plan ready to start the following spring.
Reviewed by
The survey team
PCA-certificated surveyors, Japanese Knotweed Elimination
PA1 / PA6A certificated surveyors who carry out the site visits, write the management plans and sign off the reports issued to lenders and solicitors.
Reviews the technical, legal and lender statements in this article.
What this page can't tell you
- Guidance is general. Identification, treatment choice and timescales can only be confirmed by a site visit — photographs alone are indicative.
- Lender and insurer requirements vary by institution and change over time. We state what is typically accepted, not what any named lender will accept on your case.
- Guarantee (IBG) eligibility depends on the plan chosen, the survey findings and the underwriter's acceptance. It is not automatic.
- Legal points summarise published law and guidance current at the review date. They are not legal advice.
Last reviewed · Questions on anything stated here: 07582 869979
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