Fallopia sachalinensis - giant knotweed

Plants from at least ten of the genera in the knotweed (Polygonaceae) family can be successfully grown in Finland. They include buckwheat (Fagopyrum esculentum), several so-called weeds, and others used as perennial garden plants. The giant knotweed, formerly known by the scientific name Polygonum sachalinense, is the biggest of these, capable of reaching heights of 3 metres in a single summer.

Sites for planting giant knotweed need to be chosen with some care as it spreads efficiently by means of underground shoots, and getting rid of unwanted growth is difficult. However, where there are natural limits to its growth, this is an excellent plant. Its hollow bamboo-like stalks are like fishing rods, rather thicker and stronger than those of the slender and popular Japanese knotweed (F. japonica), which also spreads aggressively. However, neither species produces seed in Finnish conditions, so more distant colonies may be the result of gardeners unintentionally spreading root fragments in compost.

At Mustila, giant knotweed grows under the Yezo spruce (Picea jezoensis) at the north end of Alppiruusulaakso (Rhododendron Valley). The spread of its jungle-like growth is limited by the nearby road and nearby forest shade. A path leading from near the giant knotweed to Atsalearinne (Azalea Slope), the so-called Maaherranpolku (Governor’s Path), ends at a plot of Japanese knotweed, so these two giant perennials can easily be compared.