Can knotweed grow through concrete?

Can knotweed grow through concrete?

Have you heard about Japanese knotweed myths and are wondering are they true? Or have you seen some pictures of plants growing from structures and are wondering can Japanese knotweed grow through concrete?

This is actually an interesting topic where myths are kind of true and there is some wisdom about concrete maintenance and gardening to be shared. That is because Japanese knotweed growing through concrete is quite true and it can happen.

The thing is, it’s not because the concrete is weaker than the knotweed. The knotweed is just good at exploiting the weaknesses in concrete.

So what does Japanese knotweed do to a house exactly? Let us find out in more detail.

What does Japanese knotweed do to a house

As you might know from the title of this article or from previous knowledge, Japanese knotweed damage has a quite bad reputation. The thing with that is that it can have a negative impact on our property if something like that is seen growing near it.

That’s just how it is, no logical reason has to be provided. You could even compare it to a rumor of water damage or something like that. When it’s bad enough, it will harm you.

The truth about Japanese knotweed is that while it’s an invasive plant and can cause harm to damaged concrete, it still can’t penetrate through healthy concrete.

Japanese knotweed and property

So what about buying a house with Japanese knotweed? It can be done, but I’d like to be sure that it’s not a problem. The plants should be far enough and you certainly shouldn’t let them spread closer to your house. Or neighbors if you like to live in peace.

If it’s not a problem when it’s far enough, can you build on land with Japanese knotweed? Sure you can, but it has to be under control and you want to know that.

If you choose to build on such a land, you might want to prepare yourself for the cost as well. It might be expensive and take up to 5 years to get completely rid of it.

Do you have to declare Japanese knotweed when selling a house

If you live in the UK, it seems like you have to. Looking at how invasive and hard to get rid of it is, it’s quite reasonable as well.

For a house buyer, it will more than likely cause extra bills. That being said, how much does Japanese knotweed devalue property?

To that, I cannot give a good answer. Quick research showed it can be anything between 10-30% of the property value. The best way to find out would be to try to look at how much it would cost to remove it.

For that you would have to have information on how big is the contaminated area and ask specialists how much it would be. After that it becomes a question do you want to take a risk and try to fix it or sell it forward for someone else to make a lottery.

Can Japanese knotweed grow through concrete?

Japanese knotweed growth capacity

Now that we got to the expensive part, how does Japanese knotweed spread exactly? It spreads by its stems, rhizome fragments, roots, and crown.

That’s the main reason it’s annoying to get rid of. You have to be sure there’s nothing left underground as it might come back from that. It can also grow from a very small rhizome.

It’s good to notice that because it can grow from something so small, it can also spread by traffic. Getting rid of it will usually take a combination of different measures like burning, chemicals, and excavation.

Plants that grow through concrete

After all of this, let us get to know how do plants grow through concrete. As I said, it can’t grow through concrete, but it can grow in the cracks.

More than likely, the concrete you see it growing in has once had a tiny little crack on it. It can be so tiny you can’t even see it with your eye with some plants.

If you’ve ever had a pavers walkway or driveway, you might have noticed that once weed starts to grow in between the pavers, it can even slowly shift them even when there are hundreds of pavers around it.

The same happens to concrete, the power of root growth is truly amazing. Tree roots have even more potential and I guess Japanese knotweed falls somewhere in between.

So plants that grow in concrete just exploit the tiny spaces they can grow in. Just goes to show how strong plant life is.

How quickly does knotweed grow? Japanese knotweed can grow 4 inches (10cm) a day so you can calculate from that how fast it spreads.

When you combine all of these, you can see how harmful it can be to houses and other structures. Roots can travel amazing distances in cracks and gaps of structures, just looking for ways to expand.

Japanese knotweed removal

Before you start with removal, you will first you will need to know how to find out if a property has Japanese knotweed. I know it sounds silly, but like said before, it spreads underground.

That means you have to look for more than obvious signs like bamboo-like stems, zig-zag stems, and the big green leaves.

It’s a good spot to begin a thought, examine one and start following how it spreads. How does little growth look etc.

So how to get rid of Japanese knotweed after I identify it? You need to use multiple means more than likely.

Herbicide, burning, manual removal of rhizomes, you need to dig in the ground. And you might have to do this for many years.

This means you have to start at once you notice you have a problem. When you cut them down, you need to dispose of them properly, not leave them on the ground.

If you use glyphosate-based weed killer, you have to be careful as it kills everything else as well. After it has affected for a week, you have to pull all of the roots out.

It’s a cut and poison process that might be repeated multiple times. At some point, it might be wise to call professionals if it seems it’s not giving in.

Also, remember to dispose of them with proper means. That way it won’t become your problem or a problem for someone else.

If you for some reason want to keep it on your property, Japanese knotweed distance from the house should always stay over 23 feet (7m).


I guess the answer to can knotweed grow through concrete was a no and yes. All concrete cracks a little when it cures and shrinks.

These little cracks can be a surface for plants to grow. Something like sealing of the concrete could help, but it’s something that can only be done to the surface.

If the root growth comes from below or side, there might be cracks you’re not aware of. Also, even sealed concrete cracks with time.

Cracking is one of the things concrete will do no matter what. For that reason, proper maintenance is good for it so that nothing will start growing on it.

I guess it is a little open is it worth buying a house with Japanese knotweed. I would think it’s a matter of how severe it is and what kind of investment it is.

If you have ways to get it under control and you’re professional in controlling it, you can see it as an investment where you will get paid by your labor.

There is always the possibility that it could go wrong as well. It’s the gambles we take when we buy a property that has a red mark on it.