Lysimachia vulgaris • Class B

Garden Loosestrife has showy, bright yellow flowers which grow in clusters near the top of the plant. Flowers have 5 petals that are joined at the base and sometimes have a red or orange eye. The base of the flowers is ringed by green sepals that have orange-brown edges. The plants’ leaves are softly hairy, 3 to 5 inches long and egg-shaped, usually growing 3 leaves in a whorl. Garden loosestrife roots form creeping stems that are partly or entirely underground. These rhizomes can be up to 15 feet long. 

It damages shoreline and wetland ecosystems by replacing beneficial native plants. It reduces habitat needed by waterfowl, wildlife, birds and fish, including several species of salmon. 

The ability of Garden Loosestrife to invade and establish itself in wetlands, lakeshores and riverbanks, threatens native species in those sensitive areas. It can out-compete most native plants, and even other invasive species like Purple Loosestrife. 

Identification of Garden Loosestrife is often complicated because of its name and appearance. It is related to a common ornamental species (Lysimachia punctata) also called Garden Loosestrife or Yellow Loosestrife. This plant looks very similar to Lysimachia vulgaris; however its blooms are situated in the leaf axils all the way up the main stem, not in clusters at the tops of the stalk. 

Once established, garden loosestrife is highly competitive and able to spread aggressively into stands of established vegetation. Garden loosestrife is able to out-compete even tough plants such as cattails and purple loosestrife. 

• Controlling Garden Loosestrife is a complex issue due to the environmental issues involved with access, movement, and sensitivity to disturbance. Early detection, which is a vital element of successful noxious weed management, is very difficult because of this species pattern of delayed blooming until it is well established. In fact, Garden Loosestrife will sometimes remain vegetative for many years before blooming. 

• Most control methods need to be applied over several years to be successful. A combination of methods will be more effective than one alone. 

• Covering with black plastic can be used in limited areas to suppress seedlings, but will not control or suppress older plants. Prevent plants from spreading by carefully cleaning vehicles, boats, trailers and other equipment after visiting infested areas. 

• Cutting or mowing can prevent seed production, but plants will re-sprout and usually bloom again the same season. Pulling is not effective, as plants break off easily. Small plants can be dug up; taking care to remove all rhizomes or the plants will regrow from remaining pieces. 

• When Garden Loosestrife is found in aquatic areas, please note that aquatic herbicides are restricted for use in Washington State to licensed applicators only. 

• Products containing the active ingredient glyphosate (used in Roundup Pro, etc.) are effective for controlling Garden Loosestrife in terrestrial (dry) environments. 

• No biocontrol agents are presently known. 

 Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photo by Leo Michels