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Japanese knotweed (Reynoutria Japonica) is a non-native, invasive plant that was imported to the UK in Victorian times. It was planted in nurseries and gardens across the country and has since spread widely across the UK, largely through the movement of soil and plant material. The species spreads through its extensive and powerful underground root, or rhizome, system, and causes damage to homes and gardens by pushing up through paths, tarmac driveways, cracks in concrete, drains and even cavity walls.

But what does it look like and how can you tell if it’s growing on or near your property?

Knotweed can be tricky to spot because its appearance changes depending on the season, so to identify it successfully you need to know what to look out for at different times of year.

How to identify knotweed

Spring...

In early spring, knotweed emerges from hibernation. Thick, red or purple asparagus-like stems pierce the ground and grow quickly, bright lime green leaves sprout as they get taller before forming hard canes similar to bamboo. By May, the plant is covered in heart, or shovel-shaped leaves which emerge alternately from purple-speckled stems in a zig-zag pattern.

Summer…

During June, July and August Japanese knotweed is in full growth, mature plants can reach up to 3 metres in height. Canes are hard, connected to distinct crowns in the ground, and leaves darker green. In late July or early August, clusters of creamy white flowers appear, hanging from the upper leaf axials.

Autumn…

During October and November the leaves turn yellow, then brown, and begin to fall, while the stems turn brown and brittle.

Winter...

Knotweed becomes more difficult to spot in winter as above-ground growth disappears, leaving just the dead brown canes standing with the distinctive crowns still visible in the ground. But the underground rhizome system is very much alive, and waiting to emerge when spring arrives.

If you’re worried about a plant in your garden you can email a photo to expert@environetuk.com for a free ID service. But don't panic, around half the photos received every week turn out not to be knotweed, which is commonly mistaken for ivy, bindweed, peony, lilac, houttuynia and Russian vine.