Plants commonly mistaken for Japanese knotweed

Plants commonly mistaken for Japanese knotweed include bindweed, Russian vine, dogwood, dock, lilac and Himalayan honeysuckle, along with Himalayan balsam, bamboo and Houttuynia. Most can be ruled out quickly once you know how to identify Japanese knotweed, because knotweed stands on its own on stiff, hollow canes.

Two quick tests

The Property Care Association (PCA) sets out two simple tests in its guidance for valuers and surveyors. Climbers such as bindweed and Russian vine can be ruled out because knotweed is free-standing, and woody shrubs with solid stems, such as dogwood and lilac, because its canes are hollow.

By the PCA's description, mature knotweed canes are typically 10 to 25 mm across, fibrous rather than woody and branching alternately in a mild zig-zag, on plants typically 2.5 to 3 m tall. The leaves are shovel- or shield-shaped, drooping clusters of tiny white flowers usually appear in August, and in autumn the leaves fall and the stems turn buff-brown, usually remaining upright through winter.

Japanese knotweed look-alikes compared

Bindweed

Bindweeds are twining climbers with triangular to heart-shaped leaves and trumpet-shaped flowers that are white, pink, or pink with white stripes. Field bindweed is a perennial that twines to 2 m, with leaves 2 to 5 cm long and flowers 1 to 2.5 cm across. Hedge bindweed has leaves up to 15 cm long, and large bindweed has large white trumpet flowers 6 to 9 cm across. Black-bindweed is an annual with flowers like those of Russian vine, but no woody base. None has stiff stems of its own, and a plant that winds around something else for support is not knotweed.

Russian vine

Russian vine (Fallopia baldschuanica) is a close relative of Japanese knotweed, but it is a climbing perennial with a thick, woody lower stem that scrambles many metres over trees, fences and buildings, twining rather than using tendrils. Its leaves are triangular with heart-shaped bases, 3 to 6 cm long and slightly more arrow-shaped than knotweed's. The small white flowers, about 5 mm across, grow in clusters, and the plant does not form knotweed's tall, stiff stems.

Himalayan balsam

Himalayan balsam (Impatiens glandulifera) is an annual that grows up to 2 m. Its stem is hollow like knotweed's, but sappy and brittle, and ranges from green to red. The leaves are the clearest difference: slender to elliptical, finely serrated and up to 15 cm long, growing opposite each other or in whorls of three to five. The pink (rarely white) flowers are trumpet-shaped, and the seed capsules explode when touched. In winter only hay-like remains and a distinctive short root are left, rather than standing canes.

Bamboo

Bamboos are evergreen, with woody canes (culms) marked by nodes and lance-shaped leaves with a pointed tip. Running bamboos spread by rhizomes. Knotweed, by contrast, dies back in autumn and leaves brown canes through winter.

Dogwood

Dogwood (Cornus sanguinea) is a woody shrub with oval leaves about 6 cm long, smooth edges and characteristic curving veins; pull a leaf apart and a stringy, latex-like thread shows. Clusters of creamy-white four-petalled flowers are followed by black berries, and new twigs turn bright red in winter.

Broad-leaved dock

Broad-leaved dock (Rumex obtusifolius) is in the same plant family as knotweed but spreads by seed rather than by rhizome. Its leaves are larger than knotweed's and grow up the stem as well as in rosettes near the ground. In winter its dead stems can resemble knotweed canes, so check whether they are hollow.

Lilac

Lilac (Syringa vulgaris) is a deciduous woody shrub with heart-shaped green leaves and, in late spring or early summer, very fragrant light blue-purple flowers in conical clusters. Like dogwood, it has solid, woody stems.

Himalayan honeysuckle

Himalayan honeysuckle (Leycesteria formosa) is on the PCA's list of plants commonly mistaken for knotweed. BBC Gardeners' World notes that it has narrower leaves than knotweed and hanging purple-and-white flowers, quite unlike knotweed's sprays of small white flowers.

Houttuynia

Houttuynia cordata is sometimes confused with knotweed, but grows to only about 30 cm and has white petal-like bracts.

Confirming an identification

A clear photo is usually the best next step. Many PCA contractors offer free identification from photos, and our photo check gives an automated, indicative result that a specialist survey can then confirm.

If it does prove to be knotweed, find out where you stand under the law and how likely it is to damage your home before deciding what to do. If you need a survey, we can put you in touch with up to three independent specialists who cover your area.