The Victorians brought us many things – the industrial revolution and technological innovation, mass transit, great architecture and art… and invasive species. Thankfully, we are much more aware of the damage that introducing a non-native animal and plant species to a country can have on native populations. Sadly, most countries are still paying the ecological price over a century later and the UK is no exception. All the weird and wonderful exotic foreign plants brought to our shores wreaked havoc on our native species. One of the most prevalent invasive species in the UK looks harmless but can be a nightmare for gardeners. It’s called Japanese Knotweed.
Identifying Japanese Knotweed
Introduced at Kew Gardens in the 1850s, it soon became a favourite of families, businesses, and government around the country, thanks to its ease of creating and maintaining boundaries with little to no maintenance required. Back then, few people knew the effect it would have on our native species and the damage it would cause to buildings. We know today, which is why gardener’s groups are keen to help identify it and encourage gardeners to help in the fight against its spread. Japanese Knotweed flowers in August making it much easier to identify, but in reality, you’ll need to remove it much earlier than this.
• The stems have a thin bamboo-like appearance with regular nodes breaking it up into sections.
• It has a red-green colour reminiscent of rhubarb in the summer and turns a regular wood colour in the colder months.
• The leaves are an attractive heart shape with the sides turned up to form a shovel.
• It has bunches of small, off-white flowers during flowering season – typically late summer from August to September. The leaves turn yellow quickly in September.
• The plant grows 2-3m (6½ft to 10ft) above ground with roots that bury deep by another 2-3m.
A Legal Obligation to Remove It
Few invasive plant species come with a legal obligation to remove it wherever it grows, but that certainly applies to Japanese Knotweed. The World Conservation Union refers to Japanese Knotweed as the world’s most prevalent and dangerous invasive species, not a label given out lightly. It is so dangerous that there are strict laws in place to enforce homeowners and landowners to remove it immediately upon identification. Ignoring any order to remove it could land owners with a £2,500 fine. If it eventually spreads to neighbouring land, the responsible person will be subject to an ASBO and more fines.
Insurers often refuse policies to properties with a known Japanese Knotweed problem or will charge a high premium until the problem is solved. The reason is that the roots of Japanese Knotweed can easily break through concrete and building foundations, leading to structural damage and instability.
What to do About Japanese Knotweed
There are specific procedures to follow for removing a Japanese Knotweed infestation. Unfortunately, it is not as simple as pulling it up by the roots, trimming or burning. The roots not only run deep, but any damage to the plant stimulates the rhizomes and encourages more growth. Cutting it back creates fragments from which it is highly likely new plants will grow. In brief, attempting to remove Japanese Knotweed by conventional means will almost inevitably lead to its spread.
The best and safest option is to hire horticulturalists that specialise in Japanese Knotweed removal – ask for accreditation before hiring. They will chemically treat the plant in the spring and summer and burn the roots in the winter. It may take several years to eradicate the plant and they will need to return periodically to check it has not returned. If you’re planning on selling your home, this should be a priority as the presence of this devastating plant can knock thousands off the price