Purple loosestrife

Stands of purple loosestrife can disrupt water quantity and quality, and negatively impact aquatic habitats.

Place of origin

Native to Asia and Europe, purple loosestrife (Lythrum salicaria) was likely introduced to North America as an ornamental plant and has since been found in sporadic locations in Alberta. In the 1990s, a purple loosestrife eradication program in Alberta was successful in reducing most locations in the province.


Prefer to grow in moist, highly organic soils and neutral to alkaline pH.


  • Purple loosestrife leaves are slightly hairy, lance-shaped, and can be opposite or whorled.
  • Flowers attach closely to the square, woody stem in a tall vertical spike; petals are pink to purple surrounding a yellow centre.


It reproduces primarily by seed, producing more than 2 million seeds per plant annually but can also spread through stem cuttings and root fragmentation.


  • Purple loosestrife infestations can displace native vegetation and alter water quality, reducing habitat for fish, wildlife and native plants.
  • Dense, tall stands in irrigation ditches, channels or storm water management ponds can disrupt the flow and availability of water and eliminate open water habitats.

Current management in Alberta

Control of purple loosestrife can be difficult, especially once well established. Methods for control/eradication by trained personnel include: careful hand-digging for isolated or small populations, repeated mechanical cutting and chemical treatment.

Care must be taken with hand digging and cutting to ensure all plant fragments are removed and disposed of. Fragments and seeds can drift with water movement or animal dispersal and result in new infestations.


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