When surveyors began looking at the extensive amount of land required for the Olympic Park in London, they met with an unpleasant surprise. With construction due to begin in 2008, in 2004 they began surveying the area required, and found over 10 acres were infested with the notorious Japanese Knotweed. Untreated, it is a plant that spreads exponentially, suffocates native species, and causes extensive damage to buildings, walls, and underground drainage systems.
A plan was formulated between the three agencies involved in the project, to eradicate the weed. Spraying with persistent herbicides where possible, and non-persistent herbicides close to waterways. Away from the water, the knotweed was scythed down under supervision and incinerated. Underground root systems and rhizomes were excavated for removal, while others were deep buried using suitable root barriers.
Although stronger chemicals could have reduced the time needed to eliminate the knotweed, they couldn’t be used around any areas designated for planting, or around any watercourses. Consequently, it was decided the use a milder chemical called Glyphosate, which takes repeated treatments over three seasons to achieve the required aim of knotweed destruction. During this period of repeated spraying, effected areas were fenced off to all personnel, to minimise the risk of the weed being spread by footfall.
In other areas, the knotweed was so well established that holes had to be dug to a depth of over five metres to remove all the root systems. What couldn’t be destroyed was reburied metres below the surface and encapsulated in welded horizontal and vertical knotweed root membranes. The remaining depth was then filled with knotweed root and rhizome free topsoil. During this process great care had to be taken to ensure no flints or other sharp objects were allowed into the hole that could pierce the membrane, and allow any live roots to work their way out.
It was an operation that took over four years to complete, and cost some £70-million. But the cost and effort has been worth it. Twelve years on the Olympic Park, one of the largest urban parks in Europe, remains Japanese Knotweed free.
Check your property
Japanese Knotweed continues to spread across the UK, and is public enemy number one for the UK’s keen gardeners. Check your gardens today, especially if they back onto wasteland or are near watercourses. Any sign of the weed should be treated immediately, or, if you’re not sure what to do, call in the experts.
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