Plants in two different genera, Lysimachia and Lythrum, are both referred to as “loosestrife.” Both of these genera can be found distributed all over the world in many different regions. In some areas, loosestrife is grown as an ornamental plant, and in others, it is an invasive species of concern. This is particularly so with purple loosestrife or Lythrum salicaria, a European native introduced to the United States in the 1800s.
Generally, no matter what the genus, loosestrife is a perennial herb with an erect growth habit. The flowers are produced in clusters and may be purple, yellow, or other colors, depending on the species. Most plants produce high volumes of seeds each year, and tend to grow rapidly. This can create a problem when the plant is introduced to an environment where it is not native, as it can compete with native plants for resources and become a biological problem.
These plants tend to prefer damp environments like those found near rivers, streams, and bogs. They have a high tolerance for wet soils, as well as poor soil conditions. Flowering can be extended, through spring and summer in warm climates. The plants are very attractive to bees, butterflies, and other animal visitors. In some regions, people grow loosestrife to attract animals to the garden, as seen in butterfly gardens or gardens in areas where people want to encourage bees to pollinate.
In areas where this plant has become invasive, a number of measures are used for control. Plants can be removed by hand before they start going to seed and safely disposed of by burning or landfilling. Simply cutting plants back can help. In other areas, biological predators like beetles may be introduced to attack the loosestrife and eradicate it. This must be done with care, as biological controls can become a problem for native plants as well. Herbicides are also available, and can be applied to areas where loosestrife infestation is total to kill off the plants and clear the area.
Once invasive loosestrife has been removed, it is necessary to replant so the plant cannot appear again. Native seed mixes can be used to give native plants a foothold. Using weed barriers can sometimes help, as the barrier will prevent any lingering seeds and plants from sprouting and displacing natives. Gardeners must be aggressive about eradicating invasive species, as a single plant in one garden can create a nuisance for the whole neighborhood.