During cold snaps such as the one most of the UK is currently experiencing it can be easy to believe that invasive plants such as knotweed die off and are no longer a threat to construction and developers.

So it may be surprising to find out that Japanese knotweed does not die off in freezing temperatures  - it is still very much alive, but it does change how it appears.

This is what actually happens:

• Above ground growth dies back

Frost and freezing temperatures kill the visible stems and leaves. They turn brown, brittle, and collapse.

• The plant goes dormant underground

The rhizome (root system) remains alive and viable below ground, even in prolonged freezing conditions.

• Freezing does NOT kill the rhizome

Knotweed rhizomes can survive severe winters, including sustained sub-zero temperatures.

• Regrowth occurs in spring

Once temperatures rise, new shoots emerge — often earlier than many native plants.

Why this matters for property and landowners

• Knotweed is still present in winter, even if you can't see it.

• Dormant knotweed can be missed during surveys if not carried out by an experienced surveyor.

• Ground disturbance during winter can spread the rhizome, making the problem worse.

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• Treatment planning should continue year-round — winter is often used for excavation or management planning.

Key takeaway - Frost kills the visible growth, not the plant itself.

Japanese knotweed survives underground and will return when conditions improve.

• Spring to early autumn (April–October) is the most effective period for herbicide treatment, when knotweed is actively growing and drawing nutrients back into the rhizome.

• Late summer / early autumn is often the most effective window for long-term control

• Treatment plans typically run 3–5 years, depending on infestation size and method

Can Japanese knotweed be surveyed in winter?

Yes - but with limitations. An experienced knotweed surveyor can still identify:

• Old canes and leaf litter

• Disturbed ground patterns

• Historical evidence of growth

• Rhizome spread risk areas

However:

• Dormant knotweed is easier to miss

• Surveys rely more heavily on experience and site context

• Findings often include precautionary buffer zones

Winter surveys are common for construction and due diligence but should be carried out by a PCA-qualified surveyor.

Why are winter works considered high risk on development sites?

Winter is a high-risk period because:

• Knotweed is invisible above ground

• Soil movement from construction works can spread rhizomes unknowingly

• Contaminated soil may be removed or reused illegally

• Discovery mid-project can cause costly delays and redesigns

This is why best practice is to:

• Survey before ground disturbance

• Clearly mark exclusion zones

• Implement a Knotweed Management Plan

• Use a Watching Brief during enabling works

Key takeaway - Knotweed doesn’t disappear in winter - it hides.

Conclusion: Freezing conditions cannot kill off knotweed, it may appear that it's gone, but don't be fooled as it will emerge stronger than ever in the spring. Early identification and planning protect budgets, programmes, and compliance.

Contact a reputable national knotweed contractor for identification or a quote.

japaneseknotweed.co.uk