Dr. Jekyll and Mr. Hyde describes a lot of invasives, and purple loosestrife (Lythrum salicaria, Zones 4 to 9) is no exception. This wetland perennial, originally from Asia and Europe, has tall spikes packed with gorgeous neon rose-pink flowers from May to September. It’s beautiful both close up and in wide drifts. The problem is that it’s a noxious weed, highly invasive everywhere in the continental U.S. except Florida. Unfortunately, it’s still sold as an ornamental in many regions. It spreads by both seed and rhizome to produce vast stands that diminish or replace native plant species and wildlife habitat.

damage
Purple loosestrife chokes out native grasses and other wetland plants, destroying food and habitat for wildlife. A single plant can produce 2 to 3 million seeds per year. Underground stems grow at a rate of about 1 foot per year. It spreads fastest in wetlands. So-called sterile cultivars (like the popular ‘Morden Pink’) are not—they can readily mix with the species.

control
• For small stands, pull plants out by hand. Be sure to get the whole root, as new plants can grow from root pieces. Destroy the plants—don’t compost them—especially if they’re flowering.
• Control larger stands by cutting plants to ground level before they flower each year. Or spot-treat plants with a glyphosate-type herbicide (Rodeo is made for wetlands).
• A good substitute for purple loosestrife is blazing star (Liatris spicata, Zones 4 to 9), a lookalike wildflower that’s much better behaved. Spiky magenta flowers from July to August attract butterflies, and the fall seeds attract birds. It’s also a host for painted lady caterpillar. 2 to 4 feet tall. 
 

 —text by Elizabeth Noll, photo courtesy of the Kemper Center for Home Gardening at the Missouri Botanical Garden