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A well-kept garden can help sell a home, but some plants may leave buyers thinking twice.
‘Garden’ featured among Rightmove’s most searched-for buyer keywords in 2025, so outdoor spaces remain high on many buyers’ wish lists. But invasive plants such as Japanese knotweed can affect property values and create extra challenges for buyers and sellers.
Here, Which? looks at how Japanese knotweed can affect house sales, what lenders make of it and the other plants buyers may want to watch out for.
Japanese knotweed is one of the best-known invasive plants in the UK. If left uncontrolled, it can damage 'lightweight structures', such as freestanding walls, paths and drains, according to a 2022 paper by the Royal Institution of Chartered Surveyors (RICS).
There are over 100,000 documented incidences of knotweed across the country, according to Environet’s live Japanese knotweed heat map. Bristol, Merseyside, Greater Manchester, Greater London and Lancashire are among the worst-affected areas. Environet, which specialises in removing invasive plants such as Japanese knotweed, horsetail and rhododendron, has been operating since 1996.
The presence of the weed in your garden can make it difficult to sell the property. A third of British adults would not buy a property affected by Japanese knotweed under any circumstances, according to a YouGov survey for Environet. The same research found that if there is a professional treatment plan in place and a price drop, three in 10 would consider purchasing the property.
It is understandable why some buyers are put off. RICS has previously described the treatment of the plant as 'expensive, disruptive and can affect the quiet enjoyment of a property for a number of years'.
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Research by Censuswide and Environet suggests homes affected by Japanese knotweed may sell for around 5% less on average. For the average UK home, that would result in a drop of around £13,500 in value.
While it is not illegal to have Japanese knotweed on your property, homeowners are responsible for stopping it from spreading. Under the Wildlife and Countryside Act 1981, it is illegal to plant or cause Japanese knotweed to grow in the wild.
It is also the seller’s responsibility to check their property for Japanese knotweed. Sellers must disclose whether a property is affected on the TA6 property information form, which covers key details buyers may need to know before purchasing a home, including flooding history, disputes and parking arrangements. The form also asks where the knotweed is located and whether a management plan is in place.
Japanese knotweed does not automatically mean you’ll be refused a mortgage. However, lenders may want more information about the severity of the infestation and whether a professional treatment plan is in place.
In some cases, buyers may need a specialist report and an insurance-backed remediation plan before a lender agrees to offer a mortgage. Unmanaged knotweed on neighbouring land can also cause concern.
David Hollingworth, of mortgage broker L&C says: 'Growing awareness of Japanese knotweed and its potential impact on structural integrity of buildings and foundations caused mortgage borrowers some big problems. Initially, valuations that picked it up could pretty much result in a straight decline with little leeway for flexibility over individual circumstances.’
He says lenders now take a more flexible approach depending on the severity of the infestation and its proximity to the property.
Hollingworth adds: ‘In many cases there may not be a major problem for lenders, although where there’s more significant evidence of damage there may be a need for a specialist report and for a remediation plan to be in place with an insurance-backed guarantee.’
It’s also important to note that Japanese knotweed is not the only plant that could concern lenders. Hollingworth explains that any plant or tree causing damage to a property, such as tree roots affecting structures, could potentially be flagged during the mortgage process.
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Join Which? MoneyJapanese knotweed looks different depending on the season. In winter, the stems die, turning brown, while the root system stays alive, but dormant, over winter.
In spring, stems regrow. According to the Royal Horticultural Society, the stems usually grow about two metres and reach their full height in late summer.
Key features of Japanese knotweed picked out by the GB Non-native Species Secretariat (NNSS) are:
To understand more about what Japanese knotweed looks like, the NNSS has produced a helpful identification sheet for the plant and other non-native species.
We asked experts about some of the other species that could be difficult to control, expensive to remove or potentially off-putting to buyers.
Ceri Thomas, editor of Which? Gardening, says marestail can be very difficult to control because of its deep roots.
Ceri says: ‘A garden covered in marestail would definitely be one I’d avoid as it’s very difficult to control and has very deep roots, so it keeps popping back up.’
She recommends spraying with Vitax SBK weedkiller after trampling plants, or digging out the roots and trying to remove as much as possible.
Ceri says large clumps of bamboo spreading across a garden are a common issue when buying a house.
Ceri added: ‘A monster clump of bamboo that’s popping up all over the garden is also a common find when house buying.’
She says buyers who want to keep bamboo under control can dig a trench around the clump that’s about 30cm deep and as wide as a spade’s blade before installing a bamboo barrier. More established growth may require specialist removal.
David Hollingworth says other invasive species, such as giant hogweed and Himalayan balsam, are less likely to be a concern for mortgage lenders because they do not usually cause structural damage in the same way as knotweed.
However, they can still put buyers off. Hollingworth says giant hogweed sap can cause burns and may require specialist disposal.
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