Japanese knotweed guide
Japanese knotweed is a hot topic at the moment; the following resources will provide you with everything you need to know from what it is and how to identify it through to remediation options and the effects Japanese knotweed can have on a property.

In addition to the short video clips we have also created a handy guide.

If you would like to check if your property has a Japanese knotweed risk, Groundsure offers a search report. Find out more.

Dr Paul Beckett, Director, Phlorum

How to identify Japanese knotweed

The history of knotweed in the UK begins around 1825 when it was first introduced to a botanic garden in Chiswick by Victorian botanists. It didn’t really take off until it won an award in Holland 20 years later and was then planted in more gardens.

Its main mechanism of spread is vegetative cuttings (in the root system), Japanese knotweed is essentially a perennial root. The root mass is like an ice burg in that there’s a lot of below ground growth that you can’t see. The crowns are the parts above the ground where the roots emerge belie the mass of root that can be several metres deep and several metres in radius beyond the crown so it’s very easy to take soil from an area affected by knotweed without realising it. As we’ve increased the amount of movement of soil and waste through construction, landfill and perhaps in the 2nd World War (through the movement of bomb rubble), the rate in which knotweed has spread has increased.

Identifying Japanese knotweed at a property can be challenging because sometimes people only focus on the leaf shape and there’s lot of other plants with a similar leaf shape to Japanese knotweed. Japanese knotweed either has a shield shaped leaf with a flat base or a heart shaped leaf which is roughly similar but has lobes at the base of the leaf creating the heart shape. It also has hollow stems with purple speckles visible rings; these nodes make the stem look like bamboo.  It also has alternate leafing pattern – at each node there is an alternate leafing or stem arrangement. Species that look similar to knotweed that can be distinguished easily will have an opposite leafing pattern.

The legal framework

The legal implications of not identifying Japanese knotweed at a property before exchange have predominantly focused around the Wildlife and Countryside Act, which states it is illegal to cause knotweed and other invasive plants to grow in the wild. However, case law has shown that this legislation is designed to protect wildlife and the countryside, and Japanese knotweed is increasingly seen as a property and people issue. This is reflected in recent changes to the law, in particular the Anti-Social Behavioural Crime and Policing Act which now includes Japanese knotweed – an Anti-Social Behavioural Order (ABSO) can be imposed on someone if they are causing a problem to the communities and other properties by allowing the species to spread.

There have also been other changes in the law – there is the Invasive Alien Species Regulations which comes from Europe, Species Control Orders which come through the Infrastructure Act (however guidance on those laws state that they are designed to protect wildlife and the countryside). The ASBO is the only one that focuses specifically on people and property issues. The most active area of law with regards to Japanese knotweed is private nuisance – where Japanese knotweed on a property is causing a significant impact on an adjacent property.

The Implications of Japanese knotweed and the remediation options

Japanese knotweed can cause damage to structures, brickwork, foundations and walls, it can grow through cracks and prise apart concrete, brickwork and tarmac. In addition to the physical damage it can cause, the effects of successful litigation are arguably greater in both cost and significance. In successful litigation cases in, addition to the treatment costs there is often a blight effect on the property which can diminish its value by as much as 20%. This can easily run from the tens to hundreds of thousands of pounds depending on how much the property is worth.

If Japanese knotweed is identified on a property it will need to be removed, it is important that the removal specialists are a member of the PCA Invasive Weed Control Group, not only because they are specialists but they are also backed by the Council of Mortgage Lenders (CML), the Building Society Association (BSA) and the Register of Security Engineers and Specialists (RSES).

There are a number of different treatment options, herbicide is probably the cheapest and easiest however, it takes a long time as the herbicide is applied to a limited area of above ground growth to affect a much larger area of rhizome. If a more immediate solution is required (quite often the case where the diminished value on the property outweighs the cost of herbicide treatment), excavation solutions are an option and could include:

  • Removal and disposal of the rhizomes offsite
  • Onsite treatment of picking out and crushing the rhizome
  • Encapsulating the rhizomes in a membrane to stop their growth