Purple loosestrife Lythrum salicaria
IDENTIFICATION — Is it a weed? Is it an ornamental? It’s both. This square-stemmed, woody perennial grows in every state except Florida, and its sale as an ornamental is prohibited in many of those states.
Purple loosestrife was imported from Europe as an ornamental in the 1800s. Its magenta flower spikes, which bloom all summer, lead to it quickly spreading across the country. One mature plant can produce 2 to 3 million seeds per year. And in wet areas, it spreads underground by about a foot per year.
FAVORITE CONDITIONS — It prefers moist soil, especially areas of standing water and full sun. There it reproduces quickly and can grow up to 10 ft. tall. The stems and roots are so tough that boats and wildlife can’t get through a large stand of it. And it’ll quickly squeeze out less aggressive native plants.
CONTROL — Hand pull purple loosestrife before it sets seed in home gardens. Eradicate large stands in late summer with glyphosate herbicides. Be sure to follow the instructions for applying any chemical, particularly near water. Parasitic insects that feed on roots and leaves have been introduced into wild areas of purple loosestrife as biological controls.