Japanese knotweed

Buddleia is growing out of a mortar joint. Why must that plant not be written up as Japanese knotweed without an identification?

Because buddleia is not Japanese knotweed, and it must not be written up as knotweed without an identification. A woody plant in a mortar joint can lever masonry apart, and that is a wall defect of its own. It is not a licence to rename the plant. This note records buddleia growing from the joint. The survey has not identified knotweed, and it has not decided the two plants are the same.

Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.

What is the fuller explanation?

Knotweed has a particular growth and is identified from leaves, stems and, in season, flowers, or by someone competent to name it. Buddleia is a different shrub, often rooted in lime mortar and cracks. GOV.UK guidance on invasive plants does not turn every shrub in a wall into knotweed. Writing the wrong name would send the solicitor and any specialist down the wrong path. The damage to the joint can still be real. The species still has to be right.

Ask the solicitor to record buddleia, not knotweed, unless a proper identification says otherwise. A wall repair and a knotweed management plan are different instructions. If someone later identifies a different plant, the papers can be corrected from that identification, not from a guess in the survey. Do not tell a lender the house has knotweed on the strength of a butterfly bush in a joint. The survey has not made that finding.

What should you ask your surveyor?

Is the plant in the joint recorded as buddleia, not as knotweed?
What identification would be needed before the name changed?
Has the mortar damage been kept separate from a knotweed claim?

What are the typical next steps?

Keep the plant named as buddleia unless it is identified otherwise.
Ask the solicitor not to record knotweed from this note alone.
Treat the open mortar joint as a wall defect in its own right.

Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.

Also asked about this

Can buddleia still damage the wall if it is not knotweed?

Yes. Roots and stems in a mortar joint can loosen bricks whether or not the plant is knotweed. The survey recorded that growth. It did not measure how far stems run inside the wall, and it did not rename the plant. Repair of the joint is a masonry question. It is not a knotweed finding.

Does a similar leaf shape justify the knotweed label?

No. A glance at a leaf is not an identification, and this visit has not supplied one. Different plants can share a rough outline and still be different species. The report names buddleia in the joint. Changing that name needs a proper identification, not a resemblance.