How to deal with invasive garden plant Japanese Knotweed

Early season spawning of alien plant species - brought into the UK and spread around the world through “human activity” since the 15th Century - is causing concern for domestic and commercial land and property owners as the destructive forces of aggressive root systems and fast, damaging growth takes its toll on concrete, brick work, tarmac and the value of property prices.

Japanese knotweed is one of the biggest and most damaging culprits. A persistent and fast-spreading perennial plant, it is listed by the World Conservation Union as “one of the world’s most invasive species”. It was introduced into Britain in 1825 and today costs UK homeowners and developers millions of pounds per year to manage and eradicate.

In the UK, the presence of Japanese knotweed is a land and a property nightmare, with the potential to devalue a house just with the visibility of one stalk. Some lenders may even refuse a mortgage on the basis of an infestation unless an accredited management plan is in place.

It is also a huge problem for property developers and land-owners who may be unaware of the scale of the problem until the purchase has been made, only to find their building projects are delayed with costs escalating until the problem is managed.

This year’s warm and wet weather means we are seeing the early emergence of Japanese knotweed growth in our customers’ premises, a whole month earlier than we’ve seen before. The speed of the spread is quite staggering but when you consider that Japanese knotweed originated in a hostile, volcanic landscape and can regrow from a root fragment that’s no bigger than a fingernail, it’s easy to see why it’s so hard to get rid of.

Traditional means of controlling Japanese knotweed involves using a chemical herbicide - a process administered by local authorities and specialists across the country. However, the problem runs far deeper.

Japanese knotweed has above-ground and below-ground propagules (a structure that can grow a new plant) that can extend as deep as 2-3m, making it even harder to control with chemicals. Using too much chemical, or by applying at the incorrect time of the year, can seriously thwart any realistic possibility of bringing this pest under control.

Our best method - aside from complete eradication through excavation - is to administer just enough herbicide to put the plant into dormancy which is a process that takes many years to achieve. The key for any successful programme is to leave it to the experts and to not disturb what you can see. Disturbing the soil around the Japanese knotweed can see infestations significantly expand into areas that have not previously seen Japanese knotweed growth.

All is not lost where Japanese knotweed is concerned - its presence in the corner of a domestic garden which is dedicated only to plants and wildlife, can either be left or controlled. But if Japanese knotweed is present where a homeowner is looking to extend the property, excavation before the foundations are laid is essential.

Andrew Ford of Inspectas advises on how to deal with the invasive plant (Image: Lorne Campbell/Guzelian)

It is ironic that a plant which was introduced in the 1800s and was loved for its “tropical grandeur” is now the scourge of many a landscape, blighting and damaging the very homes and properties it once adorned.

The key is in awareness and education - sharing information about identification and management techniques can help prevent the spread to neighbouring properties and reduce the risk of buying a very costly, already invaded property or piece of land.

* Top tips for managing Japanese knotweed:

* Early identification: Learn to recognise Japanese knotweed in its various stages of growth. Early detection is key to preventing its spread and minimising its impact on your property.

* Professional assessment: If you suspect Japanese knotweed on your property, seek confirmation from a qualified professional and arrange a survey to help establish a course of action and the cost.

* Legal obligations: Understand your legal responsibilities regarding Japanese knotweed. In the UK it is classified as “controlled waste” under the Environmental Protection Act 1990, and strict regulations govern its disposal.

* Consider control methods: Options include chemical treatment, physical removal and partial excavation. Each method has its pros and cons, so consult with an expert to determine the most effective approach.

* Avoid spread: Take precautions to prevent the unintentional spread of knotweed. Avoid disturbing soil or vegetation in infested areas and be cautious when disposing of plant material to prevent accidental propagation.

* Educate others: Raise awareness about Japanese knotweed in your community. Sharing information about identification, management techniques, and legal requirements can help prevent its spread to neighbouring properties.

* Andrew Ford is Senior Director of Inspectas Land Remediation in Drighlington.