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The dreaded Japanese knotweed

Anyone with a garden is almost certain to have heard of the menace of Japanese knotweed. An increasingly large number of unfortunates will have learned all about the problem first hand as the pernicious weed finds its way into their garden.

Even worse – as the Guardian newspaper reported earlier this year – the unseasonably warm start to this year has encouraged the growth and invasive spread of Japanese knotweed throughout England and Wales.

What is Japanese knotweed and why is it such a problem?

The Royal Horticultural Society (RHS) identifies Japanese knotweed by its botanical name Fallopia japonica. It’s a weed that spreads very rapidly, growing to a height of 7ft (2.1m) or so as it stifles all other plants in your garden – or, indeed, on any other patch of ground.

This invasive weed is already a major problem for any landowner – residential or commercial – because it is so very resilient and spreads so quickly. From a fragment of root that can be as small as your fingernail, the knotweed sinks its roots far below the surface of the ground in a network of creeping stems or rhizomes. These can grow as deep as 10ft (3m) and as far as 23ft (7m) in every direction.

Environmental impact

Once established, Japanese knotweed can have a disastrous ecological impact. In its competition with native plants, the invasive weed threatens the natural ecosystem.

Its rapid spread displaces all other plants, altering the composition of the soil in which it grows and affecting the life of essential invertebrates. As a recent article in LandlordToday highlights, Japanese Knotweed is truly a formidable invader.

The legal position

Japanese knotweed is invasive and persistent. It causes extensive damage and is very difficult to remove. To help prevent its spread, the Environment Agency classifies its stems, roots, and contaminated soil as controlled waste and it is described as such in the Environmental Protection Act 1990.

You are not legally required to remove the weed from your land, but the Environment Agency leaves landowners in no doubt that it must not be allowed to spread to other properties. The Agency warns that you can be prosecuted if you allow Japanese knotweed to spread into the wild.

Tips for managing Japanese knotweed

The Environment Agency stresses how difficult it is to eradicate Japanese knotweed once it has taken hold.

Even repeated spraying with approved herbicides, for instance, it can take at least three years to get it under control while the rhizomes from which it grows can lie dormant in the soil for many more years. Not only must you dispose of the dead plants as β€œcontrolled waste” you must also abide by the law on the disposal of the chemicals you have used.

An alternative to chemical treatment is to bury the knotweed you have cut down. If you choose this option, though, you must inform the Environment Agency at least one month before you carry out the work. You must also stick to certain guidelines – for example, the work must take place on the same site on which the weed had been growing and must be buried at least 5m deep (or at least 2m if the site is covered with a geotextile membrane).

If you are a householder who wants to dispose of Japanese knotweed by burning it, you need to ask your local council whether such a fire is permitted. Beware, though that parts of the plant – namely the rhizomes and crowns of the weed – can survive burning. In that case, you will need to bury them.

A final option is to hire a specialist contractor to do the work for you. The Environment Agency recommends that you choose a firm from the professional register maintained by BASIS (the charitable organisation for specialists working in the pesticide, fertiliser, and related sectors).

*Image Wikicommons

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