May 2023

Japanese Knotweed (Reynoutria japonica syn. Fallopia japonica) can grow to over 2.1m (7ft), suppressing all other plant growth.


Japanese knotweed in the Winter


As the plant prepares to die back (not die altogether) in the autumn months it will lose its leaves like those of deciduous trees and moves all of its nutrients down into its rhizomes, a series of underground roots and shoots. (it can spread at length depending on the maturity of the plant and the soil conditions).


Introducing herbicide at this critical point is considered to the most effective time as the plant is drawing down the nutrients into the crown and rhizome. This should be done by a professional invasive weed specialist. If you have any concerns, reach out for  a survey of the affected area.


Plants with rhizome systems like Japanese knotweed will preserve their energy and survive under the soil until more favourable conditions return. Knotweed typically will begin to remerge in about April.


Identifying Japanese knotweed in winter months


Japanese Knotweed with its hollow, purple stems and heart-shaped leaves gives way to dry, brown and brittle stalks with a dark orange centre. The canes are hollow and will collapse around each other as they die. The winter is more difficult for untrained eyes to identify Japanese Knotweed than other times.


It is not advisable to try to remove Japanese Knotweed yourself

Many types of knotweed can easily be mistaken by the untrained eye and has the potential to spread when it’s dug up

Check if you have an invasive weed for free


The best method of identification in winter is a close examination,  highlighting the stems which zigzag as they grow and the aforementioned brown and orange colouring which makes them look a bit like dark bamboo canes.


You should be especially careful when investigating a suspected invasive plant species, not just because some of them can cause harm to humans but also because there is a real possibility of spreading the plant to other unaffected areas.


Take care not to spread the plant:


  • Kick off any mud and vegetation from your boots
  • Check your clothes for any knotweed fragments
  • Call an expert for advice and confirmation






Source: UK Gov Guidance

Source: RHS weeds




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Japanese Knotweed
Giant Hogweed
Himalayan Balsam
Hemlock Water Dropwort