Butterbur, scientifically known as Petasites hybridus, is a perennial plant introduced around the world from Asia. The plant features large leaves and can reach heights of about 5 feet. Butterbur is used in herbal medicine, ornamental plantings and as a ground cover. It can also become an invasive weed when it expands beyond the intended growing area. At that time, it meets the definition of a weed as a plant growing where it is not wanted.
The butterbur plant spreads by rhizomes and seed, giving it two ways to spread beyond its intended growing area. The seeds can also spread by wind or water action, allowing the plants to expand their range outside any intended garden.
Butterbur plants feature extremely large leaves that spread up to 4 feet across. This leaf structure shades the ground, preventing other species of plants from germinating and growing. This effectively removes competition from other plants and allows the butterbur to thrive and continue to expand its growing area.
Gardeners intentionally growing butterbur commonly use a segment of the rhizome or root to start new plants. Other options include planting seeds or planting the crown or base of the plant. Starting and growing the plant is commonly less of a problem than controlling its expansion.
Butterbur plants range from 5 to 6 feet tall depending on species and variety. Flowers occur on tall stems in the spring with the large leaves forming after the end of the blooming cycle. The butterbur thrives in wet conditions and is sometimes used as a ground cover over wet grounds.