Is it Japanese knotweed?

Spring: red-purple shoots

In spring, reddish-purple shoots push up fast, often through gravel, paving and lawns. This is the easiest time to spot it and the time to photograph it for a surveyor.

Summer: stems, leaves and flowers

By summer the stands reach full height, about 2 m. The stems are hollow like bamboo, with purple speckles. The green leaves are spade-shaped, arranged in a zigzag pattern along the stem. Small creamy-white flower clusters appear at the stem tips in late summer and early autumn.

Winter: brown canes and hidden roots

After the winter dieback, dead brown canes remain. Below ground, the rhizomes have an orange core under dark brown skin and go down 1 m or more. Fragments as small as 1 cm can regrow, which is why digging or cutting it spreads it.

Identification and surveys are easiest from April to October.

Lookalikes

• Bindweed: a climber that twines around other plants, with white trumpet flowers. Knotweed does not twine.
• Bamboo: evergreen canes with narrow leaves. Knotweed leaves are broad and spade-shaped, and the plant dies back in winter.
• Himalayan balsam: pink flowers and hollow reddish stems, often by water. Also invasive, but a different plant and a different problem.
• Giant hogweed: much larger, with big umbrella flower heads. Its sap can burn skin, so do not touch it.
• Others: the RHS lists Russian vine, Himalayan honeysuckle, fish mint and small-headed knotweed (Persicaria microcephala).

If in any doubt, a photo to a PCA or INNSA surveyor is the safest identification.

Check a few clues together

No single feature is proof, so look at several at once:

• hollow, bamboo-like stems with purple speckles
• broad, spade-shaped leaves in a zigzag along the stem
• upright growth, not twining around other plants
• dead brown canes standing through winter
• orange colour inside a snapped or exposed root

Giant hogweed and Himalayan balsam are also controlled in the wild, and giant hogweed's sap can burn skin, so keep your distance until you know what it is. Do not pull up or snap plants for a closer look at the roots; that is how knotweed spreads.

Why identification matters

A confirmed plant must be disclosed on the TA6 property form when you sell, and the RICS standard looks at whether it is on your land or within 3 m of the boundary. A wrong diagnosis in either direction costs money: a misidentified plant can mean paying for treatment you do not need, and a missed one can lead to a misrepresentation claim after a sale.

What to do if you think you have it

Do not cut, strim, dig or compost it. Take clear photos of the stems, leaves and any flowers, and send them to a knotweed specialist. Having knotweed is not an offence, but you must stop it spreading and tell buyers on the TA6 form if you sell. The DIY guide explains what you can and cannot do, and prices are on the cost page.