purple loosestrife flowers

Purple loosestrife flowers

Image credit: Sigrid Resh

Purple Loosestrife

Lythrum salicaria


Purple loosestrife, a herbaceous perennial that is in the Lythraceae family, is a wetland invasive that prefers full sun and wet soil but is able to grow in shaded, drier conditions as well. Common identifying characteristics of this species include:

  • typically grows 6-9 feet tall with a square-shaped stem
  • leaves are whorled, slender, lance-shaped, and about 4 inches in length
  • produces multiple spike-shaped stalks with small, purple flowers that have 5-7 petals
  • flowers bloom from early July - September
  • produces about 2 million wind-dispersed seeds per plant
  • dense, woody rootstock that is difficult to remove in wet soils, when broken off stem and root fragments are able to re-establish roots and create new plants

For more information visit Midwest Invasive Species Information Network (MISIN).

purple loosestrife flowers

Spike-shaped flowers of purple loosestrife

Image credit: Sigrid Resh

purple loosestrife overtaking a boardwalk

Purple loosestrife invading a wetland boardwalk

Image credit: Sigrid Resh

purple loosestrife flowers

Flowers of purple loosestrife

Image credit: Sigrid Resh

KISMA Management Practices

As purple loosestrife forms thick monocultures, the plant can be particularly difficult to manage and remove depending on the size of the stand. While small stands of purple loosestrife can be manually removed quite easily, larger stands are much more difficult to remove. KISMA uses hand pulling and a form of biocontrol to manage this invasive. A leaf-eating beetle (Galerucella sp.) is sometimes used as a biocontrol agent on larger populations. These beetles will feed on the leaves and flower buds of the invasive which can greatly decrease the population. Manual management can be done following these steps: 

  1. loosen soil with shovel 
  2. pulling by hand or with the aid of tools such as a shovel is the most effective strategy, as long as care is taken to remove as much of the root mass as possible
  3. dispose of the plant in bags so as not to leave any stem fragments, seeds, or roots behind

Note: While removing purple loosestrife, it is extremely important to remove all root and stem fragments as they can reestablish themselves. It is also important to remember to wash your clothes and equipment after removal or treatment as to not track purple loosestrife seeds to other areas.

purple loosestrife eaten by beetle

Leaves being eaten by beetle (Galerucella calmariensis)

Image credit: Sigrid Resh

Native Alternatives

Whenever purple loosestrife is removed from a site, it is crucial to replace the purple loosestrife with native alternatives to keep it from growing back and to cover up any exposed topsoil. Species such as swamp milkweed, joe-pye weed (Eutrochium maculatum), blue vervain (Verbena hastata), and marsh blazing-star (Liatris spicata) are all tall herbaceous perennial flowers that look extremely similar to purple loosestrife and would make great alternatives.