History and Introduction

Yellow garden loosestrife is native to Eurasia, and is considered rare in parts of Bulgaria. It was introduced to the United States through the horticulture trade as an attractive landscape plant in the early 1900’s. This plant has been used in folk medicine as an astringent, treating wounds and other inflammation. As of 2025 it can be found in several U.S. states including Washington, Oregon, and states in the Mid-Atlantic, New England, and Great Lakes regions. 

Identification

Yellow garden loosestrife has yellow flowers in the summer, found in clusters in the upper leaf axils and at the end of 3-6-foot tall, hairy stems. These five-petaled flowers are surrounded by five sepals that have a reddish-brown outline (margin) to them, distinguishing it from other similar Lysimachia species. Leaves are lance shaped and can have an opposite or whorled arrangement, bearing dotted glands and soft hairs on the underside of the leaf. This plant is perennial, and can spread by seed and by underground stems (rhizomes). This plant thrives in wetland environments.

A similar-looking non-native plant, large yellow loosestrife (Lysimachia punctata), has sepals that are entirely green. This plant only bears flowers in the leaf axils, not at the end of the stem like yellow garden loosestrife. This lookalike plant can be found in both wetland and upland environments.

A similar-looking native plant, whorled yellow loostrife (Lysimachia quadrifolia) has leaves arranged around the stem (whorled) often in groups of four. Its flowers have yellow petals with black dots or streaks, and its stem does not have hairs. 

Damage and Concern

Yellow garden loosestrife poses a threat to wetlands as it can form dense monocultures that outcompete native species. It can grow alongside other invasive plants including purple loosestrife (Lythrum salicaria). Seeds are reported to float for one week or more, and can be dispersed by birds, increasing this plant’s chances of spreading. One study in Europe found that the seeds from this plant can be viable in the seed bank for up to 20 years. 

This plant is prohibited from sale in New York, Connecticut, and Washington. 

Management

Manual or Mechanical Control: This plant can be difficult to control due to its underground stems (rhizomes) that can generate new plants from stem fragments as small as 1cm. Small patches can be manually dug out of the ground. Some recommend covering the invaded area with landscape fabric or plastic to solarize the population, monitoring for regrowth around the edges. 

Chemical Control: Aquatic formulations of glyphosate, triclopyr, and imazapyr have been effective in suppressing populations of garden yellow garden loosestrife in Washington State. Always follow the instructions written on the herbicide label.

Planting native wetland species, such as sedges, after management can help to prevent the re-emergence of yellow garden loosestrife (Taylor 2017).

Reporting

LIISMA is currently monitoring yellow garden loosestrife as part of our Early Detection and Rapid Response Program. As reports of the species are collected, LIISMA is working with partners to delineate and manage any early emerging infestations before they become widespread. Yellow garden loosestrife is currently a Tier 2 species within LIISMA, prioritized for eradication. 

Your reports matter to us – please report the species to iMapinvasives or iNaturalist as soon as you detect it.