Japanese knotweed
Where a report pairs a possible crown with under the decking, what stays open about ground the boards were not lifted to see?
A possible crown under the decking leaves the ground beneath undecided, because the boards were not lifted. The survey paired a suspicion with a covered surface. It photographed or noted what it could see at the edges. It did not see the soil the boards hide, so it has not confirmed a crown there and has not cleared that soil either. Japanese knotweed identification needs the growth that can actually be examined. Hidden ground stays hidden. The possible crown remains only possible.
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?
Decking is a lid. Knotweed crowns sit at or just below the surface and send up canes, but a board can conceal both the crown and the first growth. A surveyor who cannot lift the deck can record a cane at the perimeter, disturbed gravel, or a seller's remark. None of those is a view of the covered soil. The report is right to leave the point open. Guessing that a crown is under the middle, or that nothing is, would invent an inspection the boards prevented.
Tell the solicitor the decking was not lifted and the ground under it was not seen. If the possible crown matters, ask for access to lift boards, with the seller's agreement, and for someone instructed to identify invasive plants to look. Do not lift them yourself as a casual test during a second viewing and then call that the survey. Until the ground is seen, do not state that knotweed is established there or that the garden is clear.
What should you ask your surveyor?
- What exactly was visible at the edge of the decking?
- Were any boards lifted during the visit?
- Who would be allowed to lift them if a further look is agreed?
What are the typical next steps?
- Treat the ground under the deck as not inspected.
- Do not confirm or clear a crown that was not seen.
- Arrange a further look with access if that ground matters.
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
Was the soil under the boards inspected?
No. The boards were not lifted, so the ground they cover was not seen. A possible crown is a suspicion at a covered spot. It is not an identification of what is underneath. Extent and presence in that soil stay open.
Does a possible crown at the edge identify the whole garden?
No. Even a confirmed plant at one spot would not map the garden, and this crown is only possible. The survey did not lift the deck and did not walk the soil beneath. Other beds were not decided by this pairing. Keep the limit where the boards are.