Reynoutria ×bohemica

Bohemian knotweed (Fallopia × bohemica) is a perennial, fast-growing grass in knotweed family (Polygonaceae), which forms dense stands. It is a cross between japanese knotweed (R. japonica) and Sakhalin knotweed (R. sachalinensis) and it features between these two. However, it may appear to grow more vibrant than the parent species.

Tall knotweeds are native to East Asia, where they have been exported all over the world to gardens as ornamental plants. The large size and an erect growth are common to Asian knotweeds. Their rhizome are perennial, but the above-ground parts are annual and new stems grow every year from the rhizome. The species are very fast growing and over a summer stems can reach up to several metres in height. Thus, bulky knotweeds produce lots of litter.

The species have been popular perennials in the garden because they are hardy, fast-growing, and easi to spread. However, the same properties have made them very difficult and harmful weeds. In Finland, Asian knotweeds are only propagated vegetatively, i.e. they do not produce seeds. The plant quickly forms dense and extensive growths on its rhizome. Thick ground stems can grow a meter a year and reach up to 20 metres in length and two metres deep. The plant is able to penetrate even asphalt. New growth quickly emerges from a fine fragment of rhizome, which is why knotweeds spread very easily to new places, e.g. along with garden waste or land masses.