Whether you manage a block of flats, are a buy-to-let landlord or you’re a builder involved in developing a new patch of ground, ensuring that the foundations and surrounding area of your property remain in good condition is critical.
One of the big challenges, particularly for big cities in England, Scotland and Wales, is the prevalence of invasive plants such as Japanese knotweed. Not only does knotweed quickly grow out of control if left untended, but it can also cause significant damage to foundations in extreme circumstances.
Not every landlord, homeowner or property developer is clued in on British plant life but it’s essential to know what you are looking for in this case. Here’s our quick guide to indentifying Japanese knotweed in all its forms.
What is Japanese knotweed?
Introduced to the UK in the 19th century, Reynoutria japonica or Japanese knotweed was originally favoured as an ornamental plant. It’s a perennial that is part of the knotweed and buckwheat family and it has gradually spread across towns and cities both here in the UK and throughout Europe.
While Japanese knotweed can be a spectacular plant above ground, what is happening beneath the soil is the most important thing for homeowners, landlords and property developers. The knotweed spreads through a complex network of rhizomes that can reach several metres into the earth making them difficult to reach.
If they develop near a building, they can grow into cracks and other defects, widening them as they grow. This is likely to cause structural damage over time, including potential subsidence. The problem is that you can’t see what is happening.
While it’s more prevalent in cities and towns, Japanese knotweed grows practically anywhere, from residential gardens to cliff faces and even beaches. There is a particular problem nowadays with railway embankments. These are not cleared as often as they used to be and have become breeding grounds for this invasive plant. If you live near a rail line, you could be closer to Japanese knotweed than you think.
What does it look like?
The answer is that it depends on the time of year. As a perennial, Japanese knotweed goes through several different growth phases, dying down over winter and then reappearing during the spring and finally growing wildly in the summer.
Spring
Once it starts getting warmer, you’ll easily be able to spot Japanese knotweed if it is growing on your land or garden. It begins as upright shoots that look a lot like asparagus tips and these tend to be a darkish red. Some variations are dark green but it’s the shape that is most distinctive.
Once Japanese knotweed starts sprouting, you can expect it to grow quickly, as much as 10 cm a day depending on the soil and conditions. This is what makes it so invasive and why other plants in the surrounding area don’t stand much of a chance.
Unusually, the plant will not start to develop leaves until it’s about a metre tall. This generally takes place towards the end of April.
Summer
As the shoots grow much taller the plant will start to develop leaves which are a lime colour and have red or purple veins in them. By the end of May, the Japanese knotweed is starting to become mature and the leaves take on the shape of a shield and the lime colour becomes a lot more vivid.
The bamboo-like stems are also highly distinctive at this point and have a silver sheen that is speckled with purple and pink. At the end of June and into July when the weather is at its hottest, the leaves turn a darker green and flowers will start to appear.
These are cream in colour and appear in small clusters. They tend to attract bees as you might expect and this is when the knotweed has the chance to migrate to other gardens and properties.
Autumn
During the Autumn, you’ll find the flowers disappearing and the heart or shield-shaped leaves will start to turn yellow and die off. The canes will also change colour and become more brittle and brown in appearance.
Winter
Come the colder months, like most perennials, Japanese knotweed loses its leaves and dies down. The canes tend to stay standing and in an established knotweed infestation, they are pretty easy to recognise. For less established areas, you may spot grass that seems to have a burnt appearance and small nodules with crowns in the soil.
What to do if you spot Japanese knotweed on your property
If you are developing a site, the last thing you want is the new foundations damaged by the regrowth of Japanese knotweed. That’s why it’s critical to survey the land and discover whether this invasive plant is present. Complete removal for a construction site can mean digging deep into the earth to remove the problematic rhizomes.
If you’re a landlord or own a commercial property, tackling Japanese knotweed as soon as it is identified is also essential. It’s not against the law to have the plant growing on your property but if it spreads to neighboring ones it can open up the potential for legal action which could leave you footing the cost of removal.
There are two choices when it comes to Japanese knotweed. You can either control its growth or pay for a professional team to remove it.
Control can be difficult, especially if you don’t live on the property or attend it all the time which is the case for most landlords. Because it grows so quickly, Japanese knotweed will rapidly spread and begin to cause problems, which is why eradication is generally the best option.
This does need to be done by a professional team who understands the nature of Japanese knotweed and how to tackle the underlying rhizome growth through a mix of digging out and chemical destruction. These businesses also tend to offer a 10-year insurance-backed guarantee which means that, if the plant does return, you’re covered and have complete peace of mind.
