By now, even the most casual gardeners are aware of the threat posed by Fallopia japonica, or Japanese knotweed, growing in their gardens.
During the summer the bamboo-like canes of the hardy weed can comfortably grow to over seven feet tall, and the rapid spread of its roots can suppress the development of plants around it.
The plant dies back in winter, but don’t be fooled by its brown, brittle state: specialists Environet urge homeowners to continue tackling the weed as it remains very much alive, waiting to emerge bigger and stronger with new shoots in the spring.
Here’s what to look out for.
What happens to Japanese knotweed in winter?
Knotweed’s bamboo-like canes will start turning brown and brittle in the winter months, which can trick gardeners into believing the plant has died or that their own efforts at treating have been successful.
Unfortunately, like many plants, knotweed’s rhizomes (creeping underground stems) remain healthy and lying dormant in the ground throughout winter.
What does Japanese knotweed look like in winter?
As temperatures begin to drop, the weed’s green heart-shaped leaves will turn brown and fall from the plant (see main picture). In late-November/early-December its hollow, bamboo-like canes will turn brown and die, although they remain standing.
When spring begins to approach, red or purple asparagus-type shoots will appear, quickly turning into green bamboo-like stems which grow at a rapid rate, reaching up to 3m in height.
What should I do if I have Japanese knotweed in my garden?
It’s very important to try to deal with Japanese knotweed as an amendment to the Anti-social Behaviour, Crime and Policing Act 2014 includes it and other invasive non-native plants.
It’s not illegal to have knotweed in your garden, but should you allow it to have a "detrimental effect of a persistent or continuing nature on the quality of life of those in the locality", you could face prosecution.
Home buyers should be particularly vigilant when viewing properties during the winter months. Deliberate concealment of Japanese knotweed is illegal and sellers are required to answer truthfully about Japanese it on the TA6 Property Information form completed during every property transaction.
How do I get rid of Japanese knotweed in winter?
Herbicide treatments cannot be used during winter as they require the plant to be in leaf, but Japanese knotweed can be dug out at any time of year using the environmentally-friendly Resi-Dig-Out method, which involves digging out the rhizome roots and sifting out every viable piece of root before returning the clean soil to the ground.
This can be done by the homeowner, but it’s worth remembering Japanese knotweed is classed as 'controlled waste' under the Environmental Protection Act 1990, meaning it must be disposed of at licensed landfill sites.
Specialist Japanese knotweed contractors are usually licensed to safely remove the weed from site but check first before employing their services. On no account should Japanese knotweed be included with normal household waste or put out in green waste.