Ben Lindley, Company Director at Japanese Knotweed Ltd.
Last reviewed on 30.
Japanese knotweed is estimated to be in approximately 5% of every residential property across the UK – so it could be in your garden and you wouldn’t know about it if you don’t know what to look for. You could also be sharing a boundary with properties affected by it, placing you at risk of encroachment. With around 27.8 million homes in the UK, this means over one million properties potentially share a boundary with knotweed-affected land.
But knotweed can be hard to correctly identified in your garden as there are several other plant species that look similar, but by looking for a unique combination of features throughout the growing season you can be more confident in suspecting knotweed. This invasive plant is highly distinctive, though it changes appearance from spring through to winter. As this blog is meant to be an ‘at a glance’ information piece, for the full intel check out our guide ‘All about Japanese knotweed’.
It’s crucial all home and land owners know how to spot knotweed because its early detection can reduce costs to remove or control it. It’s not OK to simply ignore knotweed – or not be vigilant about looking for it. Knotweed will encroach from outside your property boundaries onto your land, it’s quite sneaky in how it does this – usually underground so it’s not visible until it’s too late. In autumn knotweed still has some flowers and the above ground parts of the plant are quite distinctive, but wait until the winter and all you’ll see is a bunch of brown stems that could be overlooked as pretty much any winter shrub. If after reading our quick guide below you’re unsure – always seek professional advice.
Key Identification Features
Leaves:
Look for flat, bright-green, shovel-shaped leaves with a pointed tip and a flat base where they join the stem. Leaves of 10-15 cm in length grow alternately (not opposite each other) along the stem.
Stems:
Knotweed stems can reach 3 metres tall and look a lot like bamboo stems, being upright and hollow, but unlike bamboo they purple flecks. Green in spring and summer they turn brown and brittle in autumn and winter. They tend to form dense thickets (or stands). The stems grow in a distinctive zigzag pattern, becoming more obvious as the plant matures through the summer growing season.
Shoots:
In early spring, new shoots appear as reddish purple ‘asparagus-like’ spears emerging from the ground. As they mature the tightly curled leaves start to unfurl, forming thick foliage.
Flowers:
In late summer (August–September), small creamy-white flowers appear in dense clusters that can reach 10cm long.
Roots/Rhizomes:
Below ground, Japanese knotweed has a network of tough roots that can be as thin as spaghetti or as thick as a can. The rhizomes snap easily to reveal a distinctive bright orange inside. Note: if you suspect knotweed please don’t snap them as this is how the plant spreads – small fragments of root can grow a new plant.
Winter Canes:
In winter, the plant dies back above ground but leaves behind brown, brittle, hollow canes. These often remain standing, surrounding the knotweed crowns in the soil but can be seen flattened on the ground.
We hope you find this quick overview useful for spotting knotweed in your garden but if you’re still unsure try our free photo ID service for rapid confirmation. Spotting these features early is crucial for successful control and management of Japanese knotweed in your garden.
Here’s a typical case study of how we removed knotweed from a homeowner’s garden – in this instance by excavation.
Contact us and we can get rid of knotweed for you too – either by a controlled programme of herbicide sprays or excavation.