SHORT ANSWER: Japanese knotweed can grow up to 10cm per day during the summer months.
Japanese knotweed has a reputation for fast, aggressive growth. Not only can this invasive plant species grow through cracks in brickwork and concrete, it can do so with rather frightening speed!
Japanese knotweed's growth rate depends on the time of year. As we've discussed previously (see When Does Japanese Knotweed Grow?) the plant goes dormant during the winter months, then re-emerges in the spring.
Summer is when the plant hits its top growing speed. Japanese knotweed loves warm weather, and it has been known to grow by as much as 10cm per day during the summer months!
Like an unwanted house guest, Japanese knotweed can be difficult to get rid of. Patience and persistence are key to getting the job done properly.
Photo by Leonora Enking (View Original)
As we discussed in our blog about Japanese knotweed's growing cycle, this invasive species may appear to die off completely during the winter months. But appearances can be deceptive.
When selling a property in this country, you have to fill out a TA6 form, which includes this question:
Is the property affected by Japanese knotweed?
☐ Not known
It's important for sellers to answer this question truthfully, because Japanese knotweed is an invasive species that can grow very rapidly and may cause structural damage if it grows through cracks in a wall or foundation. Homes with Japanese knotweed are notoriously difficult to sell, and getting rid of the plant can be an long and costly process.
READ MORE: Selling a House with Japanese Knotweed
Unfortunately, there are some dishonest people out there, and sellers will occasionally feign ignorance of their Japanese knotweed problem for fear that it will complicate the sale. So what should you do if you've discovered Japanese knotweed on your property...and the seller didn't tell you about it?
Spring was warmer than usual this year - as you no doubt noticed if you spent it cooped up at home due to the COVID-19 (coronavirus) pandemic.
Unfortunately, a warmer-than-average spring means that there'll probably be a lot of Japanese knotweed this summer.
READ MORE: When Does Japanese Knotweed Grow?
Summer is peak growing season for Japanese knotweed, although its first shoots start to appear around April. The first half of this year may have been a chaotic and disruptive period from our human point of view, but spring 2020 brought ideal growing conditions for Japanese knotweed, with plenty of warm weather and sunshine.
Japanese knotweed causes a lot of problems in the UK, but you might be surprised to learn that this invasive species is NOT notifiable.
This means that, if you find Japanese knotweed in your garden, you are NOT legally required to notify the authorities. It is not an offence to have Japanese knotweed on your property as long as you are not allowing it to spread.
Bleach is a household cleaning product that's great for killing germs in the bathroom - but it shouldn't be used to kill weeds.
If you've got Japanese knotweed on your property, you probably don't need us to tell you how difficult this invasive species is to get rid of. Knotweed is infuriatingly resilient; supermarket weedkillers tend to be ineffective, so your only real options are excavation or long-term control with specialist herbicides.
Japanese knotweed causes a lot of problems here in the UK. It grows very quickly, it's difficult to get rid of, and it can cause structural damage by growing through small cracks in buildings. Properties with Japanese knotweed are difficult to sell, and worst of all, if you allow this invasive species to spread, you can be fined or sent to prison.
Still, if Japanese knotweed is capable of making life so difficult for us Brits, just think of how much chaos the plant must cause back home in its native Japan! Right?
Well, actually, no - Japanese knotweed isn't a big problem in Japan at all. Over there, it's just another plant.
COVID-19 (coronavirus) remains the UK's public enemy number one, and while lockdown measures have started to relax in England, they're still in full effect here in Wales. The Welsh government are currently advising people to:
- Stay at home
- Go out for food, work and health reasons only
- Work from home if possible
- Stay 2 metres from other people
- Wash your hands immediately when you get home
If you have a garden, it's probably getting a lot of use right now - after all, spring is in the air, and if you want to enjoy the longer days and get a bit of fresh air, your own back garden is the safest place to do so!
But what if, while you're soaking up the sunshine, you spot Japanese knotweed shoots emerging from your soil?
Japanese knotweed has a reputation for rapid growth, but this invasive plant's growth rate does peak and trough over the course of a year.
The growing cycle can vary somewhat depending on what the weather's doing, but there is a reasonably consistent annual pattern. Here's a rough timeline of Japanese knotweed's growing behaviour from one season to the next.
For reasons discussed in our DIY Japanese Knotweed Removal blog post, we DO NOT RECOMMEND attempting to get rid of Japanese knotweed on your own. Instead, get in touch with a specialist contractor who knows how to deal with this invasive species and ensure that it does not spread elsewhere.
Photo by dankogreen (Flickr)
Broadly speaking, there are two ways to kill Japanese knotweed:
- Herbicides - spraying the plant with weed killer
- Excavation - digging the plant up and either burying it or safely disposing of it at an approved landfill site