Petasites hybridus aka Pestilence Wort

Petasites hybridus, or butterbur, is a deciduous perennial in the daisy family. Its native range spans Europe to northern Iran, plus Algeria. It is native to Britain and Ireland. It grows in wet meadows and woods, beside streams and ditches. These damp sites suit its need for steady soil moisture. In gardens, it forms broad patches rather than neat clumps.

Plants reach about 3.3–4.9 feet [1–1.5 metres] tall. Their spread can reach 8.2–13.1 feet [2.5–4 metres]. Fleshy rhizomes run through the soil and build large colonies. The broad leaves have a heart shape and white, felted undersides. Each leaf can span 3.3 feet [1 metre]. The foliage dies back rather than staying green through winter. Plants may take five to ten years to reach full size.

Pinkish flowers appear in early spring, before the leaves unfold. They grow in tight, upright clusters with a cylindrical shape. Strong stems hold the blooms above the ground. The flowers provide an early display before the large foliage takes over. Female plants are scarce or absent across much of Britain. The supplied sources give no details about the fruit.

Butterbur prefers partial shade and wet soil. It also tolerates sun or fuller shade, according to the RHS. Clay and loam suit it, across acid, neutral and alkaline soils. It can grow in moist, drained ground or poorly drained sites. The RHS rates its hardiness as H5. Plants For A Future lists USDA zones 4–8. Damp woodland edges and bog gardens offer suitable settings. Its rhizome network can help hold soil on banks and slopes.

This spreading habit needs care in a mixed garden. Butterbur can crowd out nearby plants and may need control. The RHS suggests it for wildlife gardens, banks and slopes. Divide plants in spring to make new plants. No routine pruning is needed; dead leaves can be cleared away. The RHS reports few pest or disease problems.

Plants For A Future lists no known edible uses. It records medicinal uses of the leaves and roots. These include past use for coughs, pain and muscle spasms. Such use does not make the raw plant safe. Butterbur contains pyrrolizidine alkaloids that can harm the liver. Do not use its leaves, roots, teas or homemade extracts. Its value as a garden plant does not remove this risk.