Why Is It a Noxious Weed?
It is invasive perennial that can form dense stands of growth in Washington's wetlands and shorelines. Its behavior is similar to another noxious weed, purple loosestrife (Lythrum salicaria), that it appears it can outcompete.
How would I identify it?
It is an upright, rhizomatous perennial that can grow to a height of 3 feet or more, forming dense stands. Stems and leaves are soft and hairy. Flower clusters bloom in the summer.
Flowers are yellow, primrose-like and occur in a cluster at the top of the plant and in the upper leaf axils (the upper angle from where the leaves and stem connect). Each flower has 5 petals and sepals with reddish-brown margins.
Leaves are opposite or whorled, lance-shaped, 3.1 to 4.7 inches (8-12 cm) long, dotted with black or orange glands and softly hairy.
Stems are upright and hairy. Plants can grow up to around 6 feet in full sun and even taller in shade.
Fruit Seed Description
Seeds in capsules that open by valves.
May Be Confused With
Garden loosestrife has a cousin, (Lysimachia punctata) that is also called garden or yellow loosestrife, which looks very similar. Lysimachia vulgaris, garden loosestrife, is more likely to be found in wetland areas and has flowers that cluster at the top of the plant.
Where does it grow?
Garden loosestrife occurs in moist habitats such as fens, wet woods, lake shores, wetlands and streambanks. Please click here to see a county level distribution map of garden loosestrife in Washington.
How Does it Reproduce?
Garden loosestrife spreads by seeds and rhizomes.
How Do I Control It?
General Control Strategy
Control of this species is challenging because the species is a rhizomatous perennial, spreads by seed, and inhabits environmentally sensitive wetland sites.
Small populations may be covered with black plastic or a heavy tarp, make sure to secure edges and watch for plants trying to grow through holes or gaps. Other alternatives have not been studied. Since the species has extensive rhizomes, hand pulling or digging would be limited to very small infestations or new infestations.
For More Information
See our postcard for early detection information about garden loosestrife.
See our Written Findings for more information about garden loosestrife (Lysimachia vulgaris).
Thurston County NWCB Fact Sheet on garden loosestrife
Stevens County NWCB Fact Sheet on garden loosestrife
Whatcom County NWCB Fact Sheet on garden loosestrife
King County NWCB Fact Sheet on garden loosestrife
Control Options for garden loosestrife from Whatcom County
Control Options for garden loosestrife from King County