Wisconsin’s Least Wanted: Purple Loosestrife (Lythrum salicaria)

By Lizzy Reitzloff, Stream Monitoring and AIS Coordinator


As spring peeks in and we gradually filter out into our gardens to do some much needed maintenance and planting, keep an eye out for some of Wisconsin’s least wanted. Today, purple loosestrife, a rather showy plant, found in wetlands and some local gardens is at the top of our invasives watchlist. 

These semi-woody perennials grow 3 to 9 feet tall with as many as 50 stems on one plant, making it a dense bushy growth. They bloom from late June to early September with bright eye-catching purple to pink flowers along many of their stems, which unfortunately makes the invasive an enticing choice as an ornamental. The plant was originally introduced to North America in the 1800s from Europe and Asia for this purpose and has since spread to most states and territories.

Purple loosestrife is considered a ‘‘restricted” species according to Wisconsin invasive species regulations, meaning it is considered illegal to sell, transport, transfer, or introduce. Unfortunately, despite regulations, purple loosestrife is still occasionally grown in Wisconsin yards and sold to consumers by some nurseries as a ‘sterile variety’ despite still being able to produce viable wild-type seeds. These seeds can easily escape the confines of someone’s garden via wind or water and establish themselves in our local waterways. There, our native wetland species are outcompeted, reducing food sources for local wildlife, eliminating habitat for waterfowl, and impeding boat travel.

So as you’re buying new plants to populate your yard this year, consider some native look-alikes that are just as attractive to the eye such as Blazing Star (Liatrus sp.) varieties, Fireweed (Chamerion angustifolium), False Dragonhead (Physostegia virginiana), or some native loosestrife like Winged Loosestrife (Lythrum alatum) and Swamp Loosestrife (Decodon verticillatus).


Pictured: Dense Blazing Star – A Native Alternative (Credit to Donata Ivanova)

If you do happen to have purple loosestrife in your yard already, please consider mechanically or chemically removing them prior to seed set. One plant is thought to be able to produce as many as 2.7 million seeds annually. See Wisconsin DNR’s website on purple loosestrife for recommendations on control and/or removal depending on the size of your population. Please help to keep this noxious and invasive plant where it belongs, out of Wisconsin waterways!