Winter is the one season when herbicide has little to work on, because Japanese knotweed dies back to dormant brown canes and stops drawing anything down into the rhizome. That does not mean nothing can be done: excavation runs year-round, and winter is a good time to survey and plan for spring. Our treatment methods explain why the growing season drives herbicide timing, and why a winter find is a prompt to prepare rather than to spray.
Can Japanese knotweed be treated in winter?
Japanese knotweed cannot usefully be treated with herbicide in winter, because the canes have died back and the plant is dormant, so it does not absorb or move glyphosate down into the rhizome. Foliar spray has no leaf to land on and stem injection has no active growth to carry it. Excavation, however, can be carried out at any time of year, so a stand that needs clearing on a winter deadline is dealt with by digging out the rhizome-bearing soil rather than by spraying.
Why does the dormant season limit herbicide?
The dormant season limits herbicide because glyphosate is systemic and relies on the plant transporting it from the leaves into the rhizome, which only happens during active growth. In winter the reserves have already been drawn down into the rhizome, the canes are dead, and there is no flow to carry a herbicide anywhere. Spraying dead canes achieves nothing, which is why a credible programme times its treatments to the growing season, with late summer and autumn the most effective windows.
What can be done with knotweed in winter?
In winter the useful work is surveying, planning and, where needed, excavation. The standing dead canes still mark a stand clearly, so a survey can map its extent and produce a costed plan ready for spring treatment. Excavation and on-site works such as cell burial or a root barrier can proceed, subject to ground conditions. For a mover, using winter to get the survey and plan in place means treatment can start as soon as the plant is back in growth.
Is winter a good time to plan treatment?
Winter is a good time to plan because the season is quieter, the extent of the previous summer's growth is visible in the cane clump, and getting the survey and management plan agreed now means no time is lost when the shoots return. Arranging the plan over winter aligns treatment with the spring and summer growing season and gets ahead of the spring buying market. A winter stand of dead canes is therefore worth acting on, not ignoring, because the rhizome beneath is alive and will regrow.
Common questions
- Is knotweed dead if the canes are brown in winter?
- No. The brown canes are dead but the rhizome below ground is alive and dormant, ready to regrow in spring. A winter stand is not a cleared stand, whatever the top growth looks like.
- Can I dig knotweed out in winter?
- Yes. Excavation is not season-dependent and can be done in winter subject to ground conditions, with the rhizome-bearing soil removed to a licensed facility. It gives an immediate clearance where a deadline cannot wait for herbicide.
- When will spring treatment start?
- Herbicide treatment resumes once the canes are back in active growth, typically from late spring, with the most effective applications in late summer and autumn. Planning over winter means the programme can begin as soon as the season allows.