How to Check for Japanese Knotweed Before Buying

Check for knotweed in four steps

• On the viewing, look for tall bamboo-like hollow stems, often with purple or red speckles, growing in dense clumps.
• Check the leaves, which are shovel or heart shaped, bright green and arranged in a zig zag along the stem.
• Read the seller TA6 property information form, which specifically asks whether the property is affected by Japanese knotweed.
• Ask your surveyor or a knotweed specialist to confirm any suspect plant, because growth looks different through the seasons.

What Japanese knotweed looks like

Japanese knotweed has hollow, bamboo-like stems that can reach two to three metres in summer, with shovel-shaped leaves growing in a zig zag pattern. It spreads quickly and densely, often along boundaries, near outbuildings and from neighbouring land.

In winter the canes die back to brown, brittle stems, which can make it easy to miss. If you view in the colder months, look for the dead canes and ask whether the plant has appeared in previous summers.

Why it matters for mortgages

Japanese knotweed can affect mortgageability. Some lenders will refuse a property or require a treatment plan with an insurance backed guarantee before they lend, because the plant can damage structures and is expensive to remove.

This is why the TA6 form asks about it directly. If the seller declares knotweed, ask to see any treatment plan and guarantee. If they declare none but you spot it, raise it before you proceed.

There is no single free national map

Unlike flood zones or radon, there is no single official free national map of Japanese knotweed in the UK. Detection relies on a visual inspection, the seller declaration and a professional opinion. HomeBuyerCheck focuses on the data risks that do have authoritative sources, such as flood, ground stability and radon, while knotweed should be confirmed on the ground by a surveyor.