What to do about Japanese knotweed when you're selling your home

What is Japanese knotweed?

Japanese knotweed, or Fallopia Japonica is a bamboo-like perennial plant that has become widespread in the UK since its introduction in the 1800s. Its distinctive shield shaped leaves, and purple-flecked green shoots are a common sight along train tracks and areas of wild growth throughout the country - as well as many gardens. It is particularly prevalent in the UK in southwest England, south Wales, and Greater London.

The plant was described by the UK Environment Agency as the UK’s most invasive plant species. Rhizomes (underground stems that send out shoots) can remain dormant for several years. Even the smallest pieces can quickly sprout into plants. It usually takes about 3 years of treatment to thoroughly kill Japanese knotweed.

How does Japanese knotweed affect house prices?

The thing that makes Japanese knotweed so invasive is its ability to exploit the weaknesses of structures and the ground around it. It is relentless in its search for moisture. Its rhizomes are able to push through asphalt, gaps in brick, and weaknesses in concrete. It is also commonly found in drains, where it’s made a home looking for water, but is ultimately very damaging when it grows so large that it blocks and breaks the pipes.

Having Japanese knotweed in your garden can make it very difficult for an interested buyer to get a mortgage. This is because of its potential to cause a lot of damage to your property, whilst being notoriously difficult to get rid of. Without assurance that the problem is being managed, most lenders won’t see your home as suitable security for a mortgage.

This means that without a treatment plan, you limit potential buyers to just cash buyers. And even these buyers are likely to want to negotiate a discount on the sales price to compensate for the cost of dealing with the problem. The amount of discount requested varies, but can be up to 10 or 15%.

How to get rid of Japanese knotweed

Obviously, this isn’t ideal if you’re trying to sell your home. But it’s important not to rush into attempts to remove the plant.

Because of its highly invasive nature, the rules on disposal of Japanese knotweed are incredibly strict. Cuttings are classified as ‘controlled waste’. This means you can’t let any plant material leave your garden, unless you’re taking it to an equipped disposal facility. Even then you have to make sure it's transported in a particular way.

Research has found that just 0.7 grams of rhizome - about 10 mm - can produce a whole new plant within 10 days. It’s therefore really important you don’t even try to cut the plant back, as it’s likely to make the infestation worse. You could receive a fine of £5,000, be imprisoned for up to 2 years, or receive an ASBO if you allow it to spread into the wild.

If you have a major infestation, or you plan to sell your home in the next few years, it’s best to contact a specialist. Make sure they are recommended by the Property Care Association, as they are preferred by mortgage providers. They will come and do a survey of your garden. This will include identifying whether it is actually Japanese knotweed, and the extent of the problem. They will then come up with a plan to tackle the knotweed. This will usually involve a number of treatments with a glyphosate-based herbicide, and careful removal of the remains.

The benefit of enlisting a specialist is that they will be able to issue an indemnity certificate upon completion. This can be shown to mortgage lenders, and make your home more accessible for buyers. Paying for treatment in its entirety upfront will be a bit of a financial hit, but will also mean not having to negotiate a large discount.

A specialist will also be able to ensure that the chemicals they use are compliant with the environmental regulations for your area.

What to do if you’re already in the process of selling

In the worst case scenario you only find out that you’ve got Japanese knotweed in your garden at the beginning of the conveyancing process as part of a survey on your property - well into the negotiating stage of your sale.

Unfortunately by this point it’s very difficult to put in place a treatment plan quickly enough to satisfy a buyer’s timeline. But, the alternative is to risk your buyer pulling out, or asking for a hefty discount.

The best thing to do is to encourage your estate agents to be open with potential buyers about the presence of the plant, and to get a treatment plan in place as soon as possible. This means that you limit the number of people who pull out of the sale at a late stage, and you’ve put in place steps to encourage lenders to view your property as a more appealing investment.

An experienced estate agent will be able to provide advice on how to make your home attractive to buyers despite Japanese knotweed. Find the best agents in your area here.

Most importantly, do not lie on your TA6 form. This is the property sellers' information form you will fill in for your conveyancer. If Japanese knotweed is found on your property and you've answered 'no', you could be taken to court by the buyer for misrepresentation. A professional will be able to identify and age any plants on the property, and if they were present before the sale you will be liable to pay the costs of the buyer’s survey and legal costs, along with any loss in value the property suffers by the presence of the plant.

For more information on the conveyancing process, check out our handy guide here.