Purple loosestrife (Lythrum salicaria) commonly called Lythrum, invades and destroys wetlands. The weed replaces all native vegetation, creating a dense purple landscape nearly devoid of wildlife. Although there are still parts of Western Canada unaffected by purple loosestrife, the problem is growing. Since it arrived from Europe over a century ago, the weed has infested wetlands across North America. It thrives and spreads rapidly because it has no natural enemies on the continent. Purple loosestrife causes dramatic disruption to the ecological balance.
Recent studies prove that ornamental Lythrum cultivars, which were once thought to be sterile, CAN and DO produce viable seed. When seed from domestic plants find its way into natural and agricultural areas, new strands of wild purple loosestrife sprout. Some of the common garden varieties on the weed list include "Morden Pink", "Dropmore purple", "Morden Gleam" and "Morden Rose". In nearly all cases, it spreads via pollen and seed transfer without the gardener's knowledge.
Wild and domestic varieties of purple loosestrife are on the Noxious Weed List in Alberta, Manitoba and numerous municipalities in Canada. Many concerned individuals and groups want to take immediate action to stop the spread of purple loosestrife. However, there are no herbicides registered in Canada for purple loosestrife growing in or close to water. Biological controls have recently been approved, but it will be years before enough of these insects are available for widespread use.
But there is something you can do now. Gardeners can prevent the spread of purple loosestrife by removing established plants from their gardens and replacing them with environmentally safe alternative perennials.
Height: 3 to 6 feet (1 - 2 meters)
Leaves: smooth edges, generally opposite sides of stalk, attached directly to stalk
Stalk: Square, woody, several stalks per plant
Flowers: long pink/purple spike, June to September
The entire plant must be removed to minimize the chance for regrowth. Dig out the root mass, making sure that you have removed ALL pieces. Remember, the roots can extend 30 cm (1 foot) or deeper into the soil.
Place ALL plant material in a carton so that it can dry completely without the danger of being spread by wind, water, human or animal activity. Once totally dried, it can be burned or bagged for disposal. When burning be sure that all plant matter is destroyed. When bagging, wrap securely in a dark plastic bag or container to avoid contamination at landfill sites.
Purple loosestrife can re-root from small pieces of root, stalk, seed head, or other small bits dropped from the wheelbarrow. For this reason, it is important to work carefully and be sure that no purple loosestrife plant material remains in the soil or is spread to other areas, especially water.
All work should be completed by mid-summer BEFORE the flowers begin to go to seed. New shoots that some up from the root remnants should be dealt with quickly. The site can be replanted to grass or other perennial flowers and should be reinspected for regeneration.
The nursery industry has been quick to respond to the purple loosestrife challenge. Landscapers and gardeners can now select from a wide variety of alternative perennial plants which pose no threat to the environment. The following is a small sampling of what's recommended in western Canada. See your local nursery or garden center for details on purple loosestrife replacements.
There are a wide variety of lilies with a vast range of colors. Different varieties flower from early summer to late fall and may grow as tall as six feet.
Spiked Speedwell (Veronica spicata)
This mid-summer flowering perennial has blue, spike-shaped blossoms and grows to a height of a foot and a half. It does well in full sun, but also tolerates partial shade.
Siberian Iris (Iris sibirica)
This perennial stands two feet tall and flowers through late spring and early summer with white, blue and purple blossoms. It requires a sunny to partially shady site.
Spiked Gayfeather, Blazing Star (Liatris spicata)
This five foot tall native of eastern Canada had pink, purple, and white blossoms from mid-summer to early fall. It requires full sunlight to partial shade.
Garden Sage (Salvia)
This summer blossoming plant features flowers which are violet to blue. It is drought tolerant, likes full sunlight and grows from a foot and a half up to three feet tall. Garden sage may not be hardy in some prairie climates. Check with your local nursery.
Purple Coneflower (Echinacea purpurea)
Purple Coneflower grows about 3 feet tall and flowers in late July and August. It is easy to grow.
Photos of alternative plants by Louis Lenz. Cover photo by Cory Lindgren. This brochure has been prepared with help from the Canadian Nursery Trades Association, Landscape Alberta Nursery Association, Landscape Manitoba, Devonian Botanical Garden (Edmonton), Alberta Native Plant Council, Canadian Wildlife Service, Canadian Wildlife Federation, and Manitoba Purple Loosestrife Project.
For further information contact:
MANITOBA (204) 467-3269
ALBERTA (780) 422-4909
BRITISH COLUMBIA 1-800-665-3825
To report purple loosestrife infestations in wilderness or wetland areas, contact the Canadian Wildlife Federation at 1-800-565-6305.