Japanese knotweed is a harmful invasive species in the United Kingdom.
It’s found in all parts of the country and can cause significant damage in several ways.
Here’s a guide on all the damage that Japanese knotweed can cause, and what you can do about it.
How does Japanese knotweed cause damage?
Japanese knotweed is a very invasive and resilient plant.
In other words, it grows rapidly and is difficult to remove.
It is most often found in gardens. It causes damage to your property’s structure by getting into gaps and cracks in the walls and floors.
It doesn’t always directly go through solid material. It often finds the weak spots around it to push through.
However, it can go through concrete, asphalt, and other building materials.
Examples of Japanese knotweed damage
Foundations and walls
The most common way Japanese knotweed damages your house is through the foundations and walls.
Cracks in the wall are something to look out for. Weak foundations are standard when you haven’t tended to them long.
Damaged drains
Underground pipes and drains may fall victim to Japanese knotweed.
This can stop the utility system from working altogether. Or it could clog it up.
You may need to get a utility expert to come out and fix it, but this should only be after the Japanese knotweed is sorted.
Boundaries
Japanese knotweed can damage different types of boundaries, including fences and walls. It might grow over, through, or underneath them.
Paving slabs
You’ll most commonly experience this on your driveway and path.
Japanese knotweed grows through cracks on these surfaces. This will then be pushed apart as the plant expands.
How quickly does Japanese knotweed cause damage?
Japanese knotweed grows extremely quickly, at around 10 centimetres per day.
This means that within 48 hours, it could be noticeable as it grows through cracks.
It also has large underground rhizome (root) networks, which can stay dormant for decades.
Harm can be done in just a few days. It’s then about damage limitation, which is acting as fast as possible.
How to prevent Japanese knotweed damage
Check regularly for Japanese knotweed
The ideal principle to approach Japanese knotweed issues is ‘prevention is better than cure’.
However, this isn’t always possible.
Get a clear sense of its appearance and then do regular checks. Many plants look like Japanese knotweed, so get an expert to identify it.
Act immediately by contacting an expert
If you spot Japanese knotweed, you must act immediately. Each day that passes can make the situation worse.
This creates more damage to your house and a more expensive job.
Find a Japanese knotweed expert who can implement a management and removal plan.
While it’s possible to do it yourself, this is not recommended.
There are lots of regulations and legal requirements you need to follow. Paying for a specialist tends to be a worthwhile investment.
Communicate with neighbours, where appropriate
You should communicate with your neighbours when the Japanese knotweed crosses over property boundaries.
Be respectful and as cooperative as possible. Show them the issue and get your expert to speak with them.
Ideally, you should each pay for weed removal on your respective sides of the property boundary.
You may want to gather evidence of all of this in case it goes to court. But hopefully that won’t happen!
Carry out an ongoing management plan
Once your specialist has handled the situation, they should give you an ongoing management plan. If they don’t, ask for one.
This may involve herbicides, soil burial, or biological agents. You could also get a detailed report on what’s been done. This is useful if you ever need to sell your house.
Otherwise, the house value could drop significantly. This happens even if the problem is fixed because the potential buyers feel ‘in the dark’.
How does Japanese knotweed damage property value?
Japanese knotweed can greatly impact how much your property is worth.
In a best-case scenario, when the damage is small, it could reduce house value by around 15%.
But in a worst-case scenario, this can be around 25%. This is because time, money and effort are needed to remove and fix all the damage it has caused.
It’s often in your interest to get Japanese knotweed removed. At the very least you must disclose it and buyers will likely ask for a report on it.
