At first glance, Japanese butterbur (Petasites japonica) appears to be a tropical beauty and a fantastic groundcover for your back yard. But beauty can be deceiving! Its huge leaves shade out other plants. It steals nutrients and can quickly invade an entire area. It’s not yet widespread in Portland, but it is growing in some sensitive natural areas and it’s hard to get rid of. Japanese butterbur is listed as a “watch” species in Portland, but may be reclassified with a higher “B” ranking.
As its name suggests, Japanese butterbur hails from Japan where some people consider it edible with careful preparation. Some parts of the plant are poisonous. Its scientific name comes from the Greek word petasos, meaning a wide brimmed hat.
Japanese butterbur’s kidney-shaped leaves can be up to four feet wide and are fuzzy on the underside. It emerges in late winter or early spring, sometimes with clumps of white or pale yellow flowers appearing before the leaves, and can grow up to six feet tall.
Japanese butterbur spreads mostly through underground stems, and sometimes through seeds. It seems to be spreading in Portland through yard waste dumping, plant trading and when the underground stems break apart and float down streams. Gardeners sometimes plant Japanese butterbur in containers to check its spread, but this plant is an escape artist! It’s been known to spread in spite of containment.
Hand-pulling is an effective way to remove small areas of Japanese butterbur from your yard, though you’ll have to continue pulling sprouts for at least a few years. Mowing will not remove the plant but can keep it from spreading. More established populations are difficult to control and common herbicide treatments don’t seem to be effective. If you find Japanese butterbur, please contact Dominic Maze at Environmental Services to discuss control options.
Invasive species affect us all. They damage forests, streams, rivers and our property. Nationwide, invasives cause an estimated $120 billion in damages every year. In Oregon, the costs of controlling invasive weeds and the damage they cause amounts to about $125 million each year. It costs a lot less to control new invasive plants before they become infestations, but we need your help. Read more about the problems caused by invasive species and why Environmental Services is concerned about their impact on water quality.
Catch up on previous Alien Plant Invader posts: