I recently have been on several garden walks where garden clubs open memberís gardens for public viewing. I have seen many beautiful gardens, but I see an alarming pattern. Many of the gardens contained purple loosestrife. This plant was classified as invasive several years ago and those growing it are contributing to severe problems for our lakes, streams and other waterways.
Purple loosestrife (Lythrum salicaria) adapts readily to natural and disturbed wetlands. As it establishes and expands, it outcompetes and replaces native grasses, sedges, and other flowering plants that provide a higher quality nutrition for wildlife. The highly invasive nature of purple loosestrife allows it to form dense stands that restrict native wetland plant species, including some federally endangered orchids, and reduce habitat for waterfowl
Purple loosestrife was introduced to the northeastern U.S. and Canada in the 1800s, for ornamental and medicinal uses. It is still widely sold as an ornamental, except in states such as Minnesota, Wisconsin, and Illinois where regulations now prohibit its sale, purchase and distribution.
Range of Purple Loosestrife
Purple loosestrife enjoys an extended flowering season, generally from June to September, which allows it to produce vast quantities of seed. The flowers require pollination by insects, for which it supplies an abundant source of nectar. A mature plant may have as many as thirty flowering stems capable of producing an estimated two to three million minute seeds per year.
The plant also readily reproduces vegetatively through underground stems at a rate of about one foot per year. Many new stems may emerge vegetatively from a single rootstock of the previous year. "Guaranteed sterile" cultivars of purple loosestrife are actually highly fertile and able to cross freely with purple loosestrife and with other native Lythrum species. Therefore, outside of its native range, purple loosestrife of any form should be avoided.
A major reason for purple loosestrife's expansion is a lack of effective predators in North America. Several European insects that only attack purple loosestrife are being tested as a possible long-term biological control in North America.
Until the 1980s, the resistance of purple loosestrife to available herbicides gave wetland managers a limited list of compounds for controlling this hardy exotic. Although not approved for aquatic use, dicamba was used on experimental plots with modest success. Work is continuing to come up with a selective herbicide to control it.
Many organizations throughout North America have taken action to control the spread of purple loosestrife. Their response has been characterized by unparallelled cooperation. National wildlife services, state/provincial natural resource and environment agencies, universities, nursery trades associations, and conservation and community organizations have responded to the purple loosestrife invasion by raising awareness of the threat posed by this invasive plant, and how to prevent its spread.
Individuals, resource managers and community groups can make a valuable contribution to conserving our wetlands by elimating purple loosestrife.
All of the states in the upper Midwest restrict the use of purple loosestrife in gardens. If you identify your plant as purple loosestrife, dig it out and destroy it. In addition to a stout taproot, expect to find a network of shallow roots spreading from the primary plant. If the plant in your garden is holding seeds, place a paper or plastic bag completely over the seed-bearing spikes and clip them off before you begin digging, to prevent accidentally spreading seeds.
Don't think just because you don't live near a waterway the seeds from your plant won't affect lakes or streams, birds can devour the seeds and deposit them many miles awy in their droppings.
If you have this plant in your garden I urge you to destroy it. There are many alternative plants to take its place.
Here is a list of plants with purple flowers which you can use to replace any Purple Loosestrife you might have and still retain the purple coloration in your garden.
Aquilegia vulgaris 'Clementine Purple (Columbine)
Aster 'Purple Dome'
Agastache anisata (Anise Hyssop)
Campanula carpatica 'Blue Bliss'
Clematis integrifolia 'Bells'
Eupatorium 'Chocolate' (purple foliage)
Lavandula angustifolia 'Hidcote Blue' (lavender)
Meconopsis 'Hensol Violet'
Monarda 'Dark Ponticum' (bee balm)
About Paul Rodman
Paul Rodman has been gardening for over 45 years. He is an Advanced Master Gardener, and American Rose Society Consulting Rosarian. He is President Emertius of the Western Wayne County Master Gardener Association in Wayne County, Michigan. He currently serves as the greenhouse chairman of this group. Rodman has amassed over 5500 volunteer hours in the Master Gardener program.
Rodman is the garden columnist for The News Herald newspaper, in Southgate, Michigan. He has also written for the Organic Gardening.com web site.
He is a certified Master Canner and has taught classes on Home Food Preserving for 7 years.
He has lectured on various gardening topics throughout southeastern Michigan.
His favorite pastime is teaching children about gardening. For the past several years he has conducted classes for second grade students teaching them about subjects ranging from vermi-composting to propagation.