Hairy Willow-Herb
Epilobium hirsutum
Washington State Classification
Class B — Control Required (Designated)
Hairy willow-herb is a tall, attractive plant capable of escaping cultivation to form monotypic stands in natural wetland areas.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Hairy willow-herb is a semi-aquatic, softly-hairy herb that ranges in height from 3 - 6 feet tall.
Leaves
The leaf arrangement is mostly opposite, and the toothed leaves are lanceolate shaped (much longer than wide, and widest below the middle).
Flowers
The showy rose-purple flowers extend from leaf axils near the top of the plant. Flowers are approximately ¾ inch across. Each flower has four sepals, four notched petals and eight stamens. Blooms occur in July and August.
Fruit & Seeds
The seeds are in long narrow capsules. Seeds have a tuft of white hairs attached.
Impact
Hairy willow-herb is a tall, attractive plant capable of escaping cultivation to form monotypic stands in natural wetland areas. Aggressive and dense growth can crowd out native or beneficial species.
Ecology & Spread
Habitat
It is found in a wide range of moist soils, including wetlands, ditch and stream banks, low fields, pastures and meadows. Please click here to see a county level distribution map of hairy willow-herb in Washington.
Spread Mechanisms
Reproduction
It spreads by seeds and by rhizomes and adapts to its growing conditions. Axillary buds, found at the base of the stem, produce stolons. These stolons develop adventitious roots which pull the stolons into the ground where they develop into rhizomes.
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Control Methods
Mechanical
- Small infestations may be hand dug, but care must be taken to remove as many rhizome fragments as possible. Sites must be checked for re-growth from missed root fragments. Mowing may be an option to prevent seed production but will not kill the plant.