There are many myths surrounding Japanese knotweed — but can it really grow through concrete?

We’ve all seen the pictures in the papers — homes overtaken by an alien species called Japanese knotweed, with its shoots sprouting all over the place, including growing through driveways and even through floorboards in the house. From reports in the media it sometimes seems as though this ferocious plant is hell-bent on total domination, and nothing can stand in its way — and nothing will apparently kill it off.

When we hear media reports of Japanese knotweed growing through concrete, our immediate thought might be: “Wow, what kind of plant is this that it has such strength and power that it can break through something as hard as concrete.?” Such thoughts are entirely understandable.

It turns out that there’s a great deal of misinformation and suspicion surrounding this non-native species — one that’s among the most destructive in the UK today. Since it was introduced here in the 1800s as an ornamental plant, it has gone on to cause damage to properties, commercial sites, railway lines and more. To get an idea of the scale of the problem today, here is a map of Japanese knotweed infestations around the UK, courtesy of the PlantTracker site:

Weeding out Japanese Knotweed

In fact, here at Environet, we’ve discovered that most people have no idea what Japanese knotweed even looks like, and are not clear about its potential to cause major structural damage. We commissioned polling experts YouGov to carry out a survey, the results of which were exclusively published in the Daily Mail.

The survey found that just 19% of householders in the UK could properly identify this scourge of a weed, and that its distinctive heart-shaped leaves are often mixed up for those of other plants, such as bindweed, Russian vine and Houttuynia. Others think Japanese knotweed may even be common ivy, which is found in practically every garden in the UK.

Commenting on the survey, our founder and managing director, Nic Seal, said it was “very concerning” that the majority of people had heard of Japanese knotweed, but were still unable to identify it from common garden plants. “The longer it is left, the further its underground root system will spread and the more costly it will be to tackle,” he said. “But it’s not just about protecting one’s property from damage and decreased value; it is also about protecting oneself from the risk of being sued if the knotweed is allowed to spread.”

So Can Japanese Knotweed Grow Through Concrete?

The simple, and definitive, answer to the question of “can Japanese knotweed grow through concrete?” is no, it cannot. No matter how virulent this weed is, it does not have the force to break through brick or concrete. What it does do, though, is exploit cracks and fissures in buildings as its roots expand and seek out moisture to fuel its growth. Once they’re in these structural weaknesses, they will naturally expand and this may cause the surrounding concrete to shatter.

“If left untreated, Japanese knotweed will grow rapidly, by up to 10cm a day during the summer months, pushing up through cracks in concrete, cavity walls and drains,” says Nic. This then can lead to serious structural issues with buildings, and so it’s vital that Japanese knotweed is dealt with the moment you see it growing in your garden or elsewhere on your property.

A word of caution, however: DIY efforts are bound to fail when trying to get rid of Japanese knotweed. Its large root network will keep sending up new shoots to replace those that may be chopped down or sprayed above ground. You need a specialist Japanese knotweed firm to kill off this beast of a plant once and for all.

If you suspect you may have troublesome Japanese knotweed on your property, but are having problems identifying it, Environet is here to help. Just send us some photos to [email protected] and we’ll tell you what it is, for free. You can also call us, on 01932 868 700.