Purple Loosestrife is a perennial herb 3-7 feet tall with a dense bushy growth of 1-50 stems. The stems, which range from green to purple, die back each year. Showy flowers vary from purple to magenta; possess 5-6 petals aggregated into numerous long spikes, and bloom from July to September. Leaves are opposite, nearly linear, and attached to four-sided stems without stalks. It has a large, woody taproot with fibrous rhizomes that form a dense mat.
Purple Loosestrife can be cut down or the rhizomes (roots) can be dug up. It will be difficult to control this way because it will regrow from seeds and remaining rhizomes.
Systemic herbicides, such as Shoreline Defense®, will work to kill the root of the plant.
Chemical Application Best Practices
Anytime you use chemicals treat weeds and algae, please keep in mind the following:
- Treat your pond in sections. Treat only half the pond's surface at a time. During hot weather or when treating heavy growth, it is important to treat no more than 1/4 of your pond at a time and wait the full 14 days before re-applying. This helps lower the risk of fish loss during hot weather or when treating heavy growth.
- Once the weeds have browned & died, use a weed cutter & rake to remove as much dead material as possible. This prevents an accumulation of dead plant material and muck.
- Take a proactive approach to pond management. Use PondClear, MuckAway and Pond Dye to keep your pond looking great. For more information, see our article on the Airmax® Ecosystem™.
Ask an Expert
If you are unable to identify your pond weed(s) using our Weed ID Guide, follow this article to email us a photo.