The Petasites hybridus is a perennial from the aster or sunflower family (Asteraceae or Compositae) and is commonly named butterbur, bog rhubarb or pestilence wort. The butterbur is indigenous to Europe and Western Asia.
The butterbur spreads rapidly through rhizomes that are hard to remove. Even a small fragment of a root can grow into a new plant. If you want to contain this plant it is best to place some strong foil around the roots or grow it in a pot.
The pink flowers appear in spring just before the leaves appear. They are clustered in a cone shaped panicle on a stem of about 50 centimetres (20 inches) high. The flower spikes are not very ornamental. The Petasites hybridus is dioecious. That means that there are male and female plants. The flowers of the male plants produce nectar and pollen. The pollen is collected into a white ball on top of the flower. The male flower spike is more compact than the female spike and also withers faster. The female flower spikes appear a bit later in spring and soon after that the leaves start to appear. The spike grows a bit higher and airier. In the female inflorescences there are some flowers that look like a male flower. These little flowers produce nectar to attract insects, because the female flowers do not produce nectar or pollen.
The big, rhubarb-like leaves grow in stems of about 1 metre (3 feet) high. These are the ornamental value of this plant. Unfortunately the snails and slugs love to eat them. They turn the leaves into a big gauze on a stem. After that the ornamental value is gone and what remains is an obnoxious weed.
The Petasites hybridus prefers rich, moist clay soils and in the shade or part shade. You can find it on lake shores, river banks, damp roadsides and in wet meadows.
Because of the rhubarb shaped leaves and the preferred bogy conditions this perennial got the common name bog rhubarb. The name pestilence wort is given because the root was used as a medicine against the plague. The common name butterbur is given because the leaves where used for wrapping butter.
Attracts bees: yes
Characteristic: Newly emerging every year
Exposure: part shade/shade
Flower colour: pink
Flowering time: March – April
Foliage colour: green
Fragrant flower: no
Hardiness: -30 ºC (-22 ºF)
Height: 3 ft. 3 inches (1 m)