Japanese Knotweed
Life Cycle & Ecology
Japanese Knotweed in Europe occupies two main types of habitat, one natural and one man-affected. It is particularly well-suited to growth along riversides, where it gives every appearance of being native, and along which it is able to spread naturally by water-borne rhizome or stem fragments. The other main habitat is in man-managed areas such as roadsides, railways, derelict industrial land and anywhere else it has been discarded. It also persists in gardens where it was initially planted in Victorian times for its perceived horticultural value.
![]() |
![]() |
![]() |
![]() |
![]() |
In the spring the new stems elongate rapidly, and in a matter of weeks they have put out a green canopy that excludes most of the light. Flowering in Britain, occurs in late August and September, and in places where there is an adjacent pollen source, large amounts of seed may be produced. Such seed is inevitably hybrid, and although viable under controlled conditions, it rarely germinates in situ.
The above ground growth is very frost sensitive, and is killed by the first autumn frost, the characteristic reddish-brown stems persist throughout the winter, and provide some protection for the emergent shoots in spring.
![]() |
![]() |
![]() |