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Frequently Asked Questions

What is the problem with Japanese Knotweed?

Most people have heard of Japanese Knotweed and probably think some regular treatment with a herbicide and that is the problem over and done with so what exactly is all the fuss about? However, those who have had to tackle Japanese Knotweed will know from their own experience just how much of a costly nightmare it can be.

Japanese Knotweed is characterised by tough bamboo-like stems and clusters of creamy flowers, it looks and sounds rather like an exotic visitor but the reality is anything but. Japanese Knotweed holds the title of the UK’s most invasive plant and one of the reasons for this is it can flourish anywhere including in the poorest of soils. It spreads relentlessly and overwhelms native species damaging ecosystems. It can grow through walls, tarmac and concrete so is just as much of a problem for large commercial buildings and roads as it is for domestic householders. It is amazingly fertile and thrifty and experts say that an entire plant can grow from a tiny piece of root about the size of a pea.

Where does Japanese Knotweed originate from?

Japanese Knotweed does originate from Japan and was introduced into Britain by the Victorians as an exotic import. Once they had got fed up with it, it was dug up and thrown away spreading into the wild which explains why it is still so prevalent today. Its widespread presence in the UK is down to two factors, first, its toughness and second the fact it has no natural enemies in the British Isles which is not the case in its native Japan. A company called CABI Bioscience is working on a project to develop a natural control for the weed although it will take decades to completely eradicate it throughout the UK. Planting or dumping Japanese Knotweed is an offence under the 1981 Wildlife and Countryside Act and can lead to either a large fine or two years in prison or both.

How is Japanese Knotweed removed?

The removal of Japanese Knotweed is expensive and time-consuming which explains why it can cost a lot of money. The plant has roots which can spread up to seven metres wide and three metres deep so huge areas have to be dug up to remove the plant in its entirety. There are also strict legal controls about how the weed is disposed of and the soil it has grown in has to go with it as even the tiniest little bit of root which is left will cause the plant to re-grow again.

Contaminated soil is classed as controlled waste and it has to be buried at a minimum depth of ten metres either on-site or taken away by a licensed operator to a designated landfill site where it needs to be buried to a depth of five metres. Many landfill operators will not accept it and if you find one that will, they will usually charge a premium rate to get rid of it.

You may need a specialist site survey for accurate Japanese Knotweed removal cost

The purpose of this is to double-check the identity of the weed although it is pretty easy to verify it by checking samples against pictures online and, to confirm the extent of the problem and the best removal option. A management plan will be produced which will include details about the scale of the Knotweed, its origin and the extent of the affected soil. The plan will consider any site restrictions which could impact on the removal of the plant and also highlight any liabilities which may be associated with the property

Can you treat Japanese Knotweed with chemicals?

Treating the weed with chemicals can take years and years but it is cheaper even over a long period of time compared to excavating a site and organising controlled disposal. There has been a well-known road scheme near Fareham in Hampshire which stalled due to the presence of Japanese Knotweed on site and because the county council decided to spend three years removing the weed by treating it with herbicide which cost £5,000 as opposed to the alternative charges to dig it up and remove it which was priced at £250,000. Of course, the other problems with herbicides is that they have an environmental toll on other plant species and animals which can make them unpopular or unusable. What can make Japanese Knotweed an even tougher nut to crack is that it can lie dormant in the ground for several decades and will start to flourish again when disturbed – it really has the most sophisticated system of predation. But one thing you cannot do when faced with a Japanese Knotweed problem is nothing: it will only spread and get worse.

What are the legal and financial implications of a Japanese Knotweed infestation?

It is not illegal to have Japanese Knotweed present on your land but you may find yourself running into problems with neighbouring landowners if you do not deal with it and remove it and also you will experience problems when you try to sell. It is illegal to introduce Japanese Knotweed and or if it is already present, allow it to spread.

• If you are marketing your property then expect to experience a hit in the property value if you have Japanese Knotweed present, some industry experts estimate a fall in the value of between 20% and 25%
• Some mortgage lenders will not advance funds on a property affected by Japanese Knotweed or even a property which is free of the plant but where it is present on neighbouring land. This can be circumvented by putting in place a management plan with an insurance backed guarantee and this usually frees up the buyer and the seller to proceed with the transaction
• If you have Knotweed present on your property and it spreads to a neighbour then they could have legal recourse against you and seek to recover their gardening cost of having it removed

How to find a reputable Japanese Knotweed clearance company

Like finding any contractor for work around your property, it can be difficult to make a good choice. Here are some tips to guide you:-

• If possible go via a trusted recommendation but do bear in mind that your Japanese Knotweed problem could be quite different to the person who has recommended a company and so the price might vary significantly
• Check out the level of experience your prospective contractor has both in terms of the type of work they have done before and also how long they have been in business for
• Do some online research and check them out before you hire them – negative or bad reviews are bound to come up
• Always make sure that whoever you choose will include an insurance backed guarantee as part of the work. This is aimed specifically at covering any further costs caused by re-growth within a defined period after the removal has taken place, commonly ten years. This should include regular inspections within the first twelve months – these are usually quarterly – and an annual site visit and report for the entire duration of the warranty period

Japanese Knotweed has to be dealt with reasonably promptly but it is nonetheless important to take sufficient time to find the right contractor and also to agree on the best method of eradication and disposal.

For more general information on the disposal of garden waste, please take a look at the government website, and The Royal Horticultural Society for more information on Japanese Knotweed.