Invasive plants - Giant hogweed
Invasive plants are non-native plant species that have been introduced intentionally or accidentally by humans outside their area of origin and that reproduce and spread extensively, to the detriment of native species. Most often originating from other continents, they profoundly disrupt ecosystems and reduce local biological diversity.
It can reach a height of 3 or even 4 metres, with a stem up to 10 cm in diameter. Its leaves are also impressive, particularly those at the base, which can grow up to 3 m long. The white flowers are grouped into large umbels up to 50 cm in diameter. These enormous dimensions limit confusion with other similar species, such as common hogweed (Heracleum sphondylium), which is native and also of some apicultural interest, without being invasive.
Giant hogweed is a biennial species (first year: germination and leaf production; second year: production of flowers and seeds) that prefers moist soils rich in organic matter. In Valais, it is widely distributed in the Rhône plain and in the lateral valleys, where it flowers from July to October. Frequently found along forest paths, riverbanks, in meadows and even in inhabited areas, it competes everywhere with local flora.
Control efforts are intensive in our canton, where authorities do not hesitate to enter private properties to eradicate it. Moreover, it is strongly discouraged to uproot it oneself or even to touch it, as this plant is particularly toxic. Its sap contains a photosensitising substance, furocoumarin, which can cause severe skin burns when contact is combined with exposure to sunlight.
The shape of the umbels and their large surface area constitute a powerful attraction signal for bees, which find in the countless small flowers very abundant nectar as well as pollen of a cream-white colour.
Despite its decorative appearance and its undeniable melliferous properties, giant hogweed is a dangerous plant that must be eradicated without exception!
Sources
J. Piquée, Les plantes mellifères mois par mois, 2014
T. Silberfeld, C. Reeb, Les plantes mellifères, 2016
See also