How to Spot and Tackle Japanese Knotweed

The discovery of Japanese Knotweed (Fallopia Japonica) can jeopardise the sale of a property, so it makes sense to be one step ahead, saving you a lot of hassle and making sure the sale goes ahead. All too often, the plant is discovered by the mortgage surveyor, resulting in delay, price renegotiation and even the loss of sale.

Here are our eight top tips on what to look out for, and what to consider if you believe Japanese Knotweed exists on your property or the property you are looking to purchase.

Learn how to identify it

Japanese Knotweed looks quite different at its various growth stages throughout the year which can make it difficult to identify.

In spring, red or purple asparagus type shoots will appear, quickly turning into green bamboo-like stems, which grow at a rapid rate.

By early summer knotweed is usually fully grown; shooting up to 3 metres in height, it spreads rapidly and can push up through asphalt, cracks in concrete, driveways, cavity walls and drains in its quest for light and water.


The plant flowers in late summer, developing clusters of spiky stems covered in tiny creamy-white flowers. The leaves are luscious green in colour and usually flat and often shovel or heart shaped in appearance.

In late autumn the leaves will fall and the canes turn dark brown. The plant then remains dormant during the winter months before sprouting back to life in Spring.

However, if in doubt, ask an expert to confirm any suspicions you may have. Knotweed specialists, Environet, offer a free identification service where homeowners who are worried about a plant can send a photograph for review to

How big is the problem?

Japanese Knotweed may look small and contained but don't underestimate the scale of the potential problem. The plant has an extensive rhizome system extending 2 - 3 metres laterally from the visible plant and up to 3 metres deep.

Ask an expert for a pre-sale site survey to confirm the extent of the problem and the cost of dealing with it. If a purchaser is faced with the cost of eradicating the Japanese Knotweed, they will negotiate it off the price.

Can Japanese Knotweed damage the property?


In its quest for water and light, Japanese Knotweed can exploit any weakness in the fabric of a building - for example expansion joints in concrete, cavity walls, weaknesses in broken mortar between paving slabs or bricks. It can also damage drains and sewers.

While structural damage is rare in most residential situations, if left unchecked, a mature infestation of Japanese Knotweed can cause damage. Get an expert to assess the situation as soon as possible.

What should I do about a site survey?

An initial discussion with a Japanese Knotweed eradication expert should help to clarify the extent of the problem and in most cases, photographs will be enough to quote for a solution.

For larger areas and commercial development sites, a good contractor will be keen to come and see the site for themselves before quoting.

What are the treatment options?

There is more than one way to deal with the problem and the right solution will depend on a number of factors such as the site conditions, future plans for the site, budget and time scales.

The available methods fall into two broad categories:

  • in situ herbicide treatment; 
  • or physical removal.

An expert will outline the pros and cons of all the options fully - they can vary greatly in terms of financial cost and environmental impact as well as in time taken and efficacy.

Can the sale of the property proceed without treating the Japanese Knotweed?

It is virtually impossible to secure finance on land or property with Japanese Knotweed on or adjacent to it.

In most cases this means there's no deal until the problem is dealt with. UK banks and lending institutions are usually satisfied if an approved contractor can guarantee their treatment of the problem. It is in your interests to deal with the problem to avoid it ruining your chances of buying your prospective property.

Is the work guaranteed?

Most companies offer a guarantee but do read the small print - these guarantees are not yet insurance backed although may rely on professional indemnity insurance if things go wrong.

Even more importantly, make sure you have a detailed post-treatment management plan agreed with their chosen contractor. It's easy to negate a guarantee or warranty by disturbing the soil within a year of herbicide treatment, for example.

Will it come back?

Depending on the treatment method and notably with herbicide treatments, there is a possibility of some minor regrowth but this should be covered in any post-treatment management plan.

Any regrowth is initially weak and if dealt with swiftly and correctly, should not pose any lasting problem.



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