Purple loosestrife is a List A noxious weed. It grows as a semi-aquatic perennial forb. Originally from Eurasia, it was brought to North America as an ornamental but has escaped. It grows to 6-10 feet tall and can be found along the edges of waterbodies, creeks, and rivers. It is often found growing within cattails and can be hard to spot when new to an area.
The flowers are purple, ¼-½ inch wide, with 5-7 petals in long racemes (flowerheads). Plants begin to flower in June. Each plant can produce 2.7 million seeds that may stay viable for 2-3 years.
Plants have lance-shaped leaves that are about ½ inch wide and 1-3 inches long. Leaves have distinctive veins parallel to the leaf edge. Stems are 4 to 6-sided, erect, and branch at the ends. Plants may have as many as 30 stems. Roots are fibrous and extensive.
Purple loosestrife reproduces by seed and plant fragments. The small seeds can easily be carried by water. Once established, Purple loosestrife will displace native wetland species and diminish wildlife habitat.
What You Can Do
Garden responsibly. Don’t plant a pest.
Keep ornamentals contained.
Report sightings of Purple loosestrife to your local weed manager.
The Northwest Invasive Plant Council (NWIPC)
CDA purple loosestrife information
The Nature Conservancy – Element Stewardship Abstract
Invasive Species Compendium