Can knotweed grow through concrete?
Some companies state that Japanese knotweed can cause damage to concrete Tarmac and other hard surfaces.
Japanese knotweed (Fallopia japonica)
Is a highly invasive plant species. It has been known for its ability to grow through a variety of surfaces, including concrete. The plant does have a very strong root system. It can penetrate cracks and crevices in concrete, asphalt, and other hard surfaces.
(underground stem) of the plant can grow to a depth of 3 meters and can extend up to 7 meters horizontally. Moreover, It can grow through small gaps and cracks in the concrete. However, it’s important to note that concrete is a hard and durable material. if the concrete has been laid correctly. I.e. compacted, vibrated, reinforced, Japanese knotweed will grow around it, not through it.
Part of the issue with Japanese knotweed is that Rhizomes from this plant can spread seven meters horizontally. As can be seen in the photo above the roots have spread under the surface of the concrete to the edge. Consequently, If the knotweed is cut the plant will grow and swell. This may cause cracking to the surrounding hard surface. Therefore the best way to resolve this problem is to remove the concrete slabs. Let the Japanese knotweed grow then chemically treat it.
Digging out the plant
The trouble with digging out Japanese knotweed is that if the plant is close to a building say within one meter. The rhizomes could have potentially spread under the foundations making it impossible to remove the Japanese knotweed without undermining the building and its foundations. the environment agency preferer that Japanese knotweed is always treated institute to prevent the spread of the plant off-site to other locations. Some companies will always recommend mechanical removal as this process is more lucrative for them.
Note, it is not illegal to have Japanese knotweed growing in your garden as long it’s not spreading to a neighbouring property.