Japanese Knotweed Surveys

Japanese knotweed is the one plant that can stop a house purchase. Lenders ask about it,
sellers must disclose it on the TA6 form, and a confirmed infestation close to a building can
knock a meaningful sum off value and make a mortgage offer conditional on a treatment plan with
an insurance-backed guarantee. A survey settles whether what you are looking at is knotweed, how
far it extends, and what it means for the transaction.

How to identify Japanese knotweed

The plant changes appearance dramatically through the year, which is why so many
identifications are wrong in both directions.

• Spring — red or purple asparagus-like shoots pushing through, rolled dark
  green leaves unfurling as they grow.
• Summer — hollow, bamboo-like canes with purple speckling, growing to two or
  three metres. Leaves are shield or shovel shaped with a flat base and a pointed tip, arranged in
  a distinctive zig-zag along the stem.
• Late summer — clusters of small creamy-white flowers.
• Winter — canes die back to brown, brittle, hollow stems that stay standing.
  The crown and rhizome survive underground and will regrow.

The zig-zag stem and the flat-based shield leaf are the two features that most reliably
separate it from the plants it gets confused with: bindweed, Russian vine, bamboo, dogwood and
houttuynia.

What a knotweed survey covers

We inspect the property and, where access allows, the neighbouring land within seven metres of
the boundary, because knotweed rhizome commonly arrives from next door or from an adjoining
railway or watercourse embankment. The report records the extent of the stand, the distance to
the building and to any drains or hard surfaces, an assessment of the risk under the recognised
management categories, and what a treatment or removal plan would need to involve.

What it means for a mortgage

Most lenders will proceed where the knotweed is more than seven metres from the habitable
structure and a professional treatment plan with an insurance-backed guarantee is in place.
Closer than that, or where there is visible damage to hard surfaces or drainage, expect a
retention or a refusal. The guarantee matters as much as the treatment: it is what transfers to
the next owner.

Indicative costs

Ranges below are typical UK market fees for the work described, shown so you can budget. They are not a quotation. We give a fixed, written fee for your specific property before any work starts.

Service	Typical cost
Identification from photographs	Often free or nominal
Site survey and written report	£200 – £400
Management plan with guarantee	£400 – £700
Herbicide treatment programme (3-5 years)	£2,000 – £4,000
Excavation and removal	£5,000 – £20,000+

Knotweed surveys in Canterbury and Kent

Kent has well-established knotweed along the rail corridors and the Stour, and along the
former industrial land at the edges of Canterbury, Ashford and the Medway towns. If your survey
has flagged a suspect plant, or a neighbour’s garden has something you are unsure about, we can
identify it and set out where you stand before you commit.

Frequently asked questions

Do I have to declare Japanese knotweed when selling?

Yes. Question 7.8 of the TA6 property information form asks directly, and answering incorrectly has led to successful misrepresentation claims.

Can I get a mortgage on a house with knotweed?

Usually, provided it is far enough from the building and a treatment plan with an insurance-backed guarantee is in place. Each lender sets its own threshold.

Does knotweed always reduce the value?

Where treatment is under way with a transferable guarantee the effect is often small. Untreated growth against the building is a different matter.