Invasive plant: buddleia

Buddleia (scientific name: Buddleja davidii) is a shrub also known as the “butterfly bush”. Despite its appealing name, it is an invasive plant whose spread should be strictly limited.

Buddleia is a large shrub reaching 2 to 5 metres in height, originally from China and introduced into Europe in the 19th century for ornamental purposes. Its spectacular flowering, which lasts from June to September, is abundant and highly fragrant. The inflorescences take the form of conical spikes 20 to 50 cm long and bear numerous tubular flowers about 1 cm in size, coloured deep purple-violet.

Very hardy and resistant, and able to adapt to all types of soil, buddleia has spread rapidly throughout Switzerland, particularly in urban and peri-urban areas. This is due to the production of enormous quantities of seeds, which germinate even under the most unfavourable and unexpected conditions. Its growth is so rapid that within a few years it forms dense vegetation that prevents coexistence with native species. It colonises all kinds of habitats: wasteland or stony ground, embankments, roadsides, hedges, old walls, paths, etc.

Bees are attracted not only by the fragrance of the flowers but also by visual cues that allow them to collect nectar in rows of flowers. However, the short length of their tongue and the narrow shape of the flower corolla prevent them from fully benefiting from this resource.

In Valais, buddleia is present throughout the Rhône valley and in the side valleys at lower altitudes. Plants should be uprooted before seed maturation, taking care to remove as much of the root system as possible. As with other invasive plants, it is recommended to report their presence to the relevant authorities.

Ultimately, rather than being beneficial to butterflies and bees, this shrub is actually detrimental to them, as it suppresses native nectar- and pollen-producing plants that provided them with a better food supply.

Sources

J. Piquée, Les plantes mellifères mois par mois, 2014

T. Silberfeld, C. Reeb, Les plantes mellifères, 2016

Infoflora.ch

2302_18 Cantonal concept for the control of invasive neophytes.pdf