Purple loosestrife has spikes of bright purple or magenta flowers that bloom in July to September. Its stems are square and six-sided. Long or lance-shaped leaves grow up to 4 inches long. They are arranged in pairs or whorls of three along the stems.

In autumn, the leaves often turn red for about two weeks before fading and falling off. Purple loosestrife can grow to six feet tall.

Reproduction and Life Cycle

Purple loosestrife spreads rapidly from seeds, roots and stem fragments. A single mature plant can produce more than 2 million seeds per year. Wind, water and animals spread the seeds, which grow into new seedlings the following spring.

It can reproduce asexually when its thick, fleshy roots produce new shoots. This allows the plant to spread about one foot per year. New plants can also grow from stem fragments when plants are cut or mowed down.

Did You Know?

  • Purple loosestrife spread to the U.S. in the 18th and 19th centuries when ships inadvertently carried the plant’s tiny seeds in their ballast and shipments. It was also introduced purposefully in certain areas because of its beauty and value as a healing herb.
  • It is considered to be invasive because it grows rapidly, produces many seeds and has no natural predators. The plant quickly establishes itself and crowds out native wetland plants.
  • Never plant any variety of purple loosestrife in your garden. Even seed-free varieties can cross-breed with invasive strains to make seeds.

Sources and Additional Information