Along with “subsidence” and “damp”, there is a new utterance that is guaranteed to make any homeowner or landlord’s heart sink – “Japanese knotweed”.
Japanese Knotweed (or Fallopia Japonica) was brought to the UK in the mid 19th century by explorer Philipp Franz von Siebold. He came across the plant growing on the side of a volcano and found that it was so admired for its beauty that it was named the “most interesting new ornamental plant of the year” by the Society of Agriculture and Horticulture at Utrecht in Holland in 1847.
Little did we know back then, as the Royal Botanic Gardens in Edinburgh flogged the plant to nurseries, this exquisite bamboo-like plant would usurp ivy as the fast-growing scourge of gardens around the country.
Like ivy on steroids, Japanese Knotweed can work its way into walls, with foundation-ravaging roots which can grow up to three meters in depth and seven meters in any direction.
Naturally, this causes some problems for properties – £170million worth a year of problems to be precise – and has since been demoted from its flattering accolade from two centuries ago and placed on the World Conservation Union’s “worst invasive species” list. Ouch.
How to spot it
For such a persistent plant, it retires (dies back) in the winter, returning in early spring with red and purple shoots, accompanied by rolled back leaves which then grow very quickly.
By spring and summer you can expect bamboo-like shoots which grow up to 7ft tall, adorned with leaves up to 14cm in length. The leaves are large and arranged in a zig-zag pattern along the stem. By late summer you will see creamy-white flower tassels which grow up to 15cm and attract bees.
How to get rid of it
This is not a job for a trowel and some weedkiller. Many gardeners accept that they are out of their depth as the roots of this plant reaches new ones and hire a professional to rid themselves of it.
If you do decide to tackle it yourself, be sure to take on the roots and keep on top of any new ones which emerge. Not all weedkillers are created equal, so you’ll need to look for one which is glyphosate-based to make any headway.
The Environmental Protection Act of 1990 also classes Japanese Knotweed as “controlled waste”. This means you can’t just throw any remnants in your green wheelie bin. It can either be dried out and burnt, or you can call a licensed contractor to dispose of the plant by taking it to a designated landfill site.
Knotweed and insurance
It’s unlikely that your buildings insurance covers Japanese Knotweed, so it’s important to be on the lookout for it before it has the chance to either destroy your home, or land you in hot water with neighbours if you fail to address the problem and it spreads.
Unfortunately, like subsidence, Japanese Knotweed can lead to a huge drop in your property’s value, and even render it unsellable.
But there is hope in the form of Aphalara itadori. This species of psyllid from Japan is known to feed exclusively on knotweed and has already been released in spots across the UK to trial its battle tactics against the destructive plant.