Purple Loosestrife

The magenta spikes that take over a wet meadow. One mature plant sheds two to three million seeds a year, the seed moves on water, mud and waterfowl, and it is a listed noxious weed in most states. The garden cultivars sold as sterile are not sterile.

How to identify it and separate it from the natives it resembles. Square stems, stalkless paired leaves clasping the stem, and a dense magenta terminal spike - and a native Lythrum, winged loosestrife, that looks similar and should be left alone.

You must not plant purple loosestrife, and in most states you may not. What matters is recognizing it, and recognizing what it is not, because native wetland plants get pulled by mistake every summer.

The plant itself: a stout perennial three to seven feet tall, growing from a hard woody root crown that throws up thirty to fifty stiff stems. The stems are distinctly four- to six-sided, not round — roll one between your fingers. The leaves are lance-shaped and stalkless, set in opposite pairs or whorls of three, with a rounded or heart-shaped base that clasps the stem, each pair rotated ninety degrees from the pair below. From June to September every stem tip carries a dense magenta-purple spike six to eighteen inches long, the individual flowers with five to seven crinkled petals. In winter the dead stems stand as stiff reddish-brown skeletons.

Now the lookalikes. Winged loosestrife (Lythrum alatum) is a genuine native Lythrum and the one most often destroyed by mistake: it is small, two to three feet, its upper leaves are alternate rather than opposite, and its flowers sit singly in the leaf axils instead of forming a dense spike. Leave it. Blue vervain (Verbena hastata) has a branched candelabra of pencil-thin spikes with small blue-violet flowers opening in a moving ring, and stalked, toothed leaves. Fireweed (Chamerion angustifolium) has alternate leaves and four petals. Swamp loosestrife or water-willow (Decodon verticillatus) is native, with arching stems that root where the tips touch water. And the yellow and gooseneck “loosestrifes” sold in garden centers are Lysimachia, a different family entirely — some of those are aggressive too, but they are not this plant.

Why it wins: it tolerates a huge range of wet conditions from saturated muck to merely moist roadside soil, it is hardy to about zone 3, it starts growing early, it grows tall enough to overtop native wet-meadow plants, and it has essentially no North American herbivores or diseases that check it — which is exactly the gap the biocontrol beetles were imported to fill.

Seed, on an almost unreasonable scale: two to three million per plant per year, viable in wet sediment for years, moved by water, mud, waterfowl, boots and boat trailers. The crown also regrows from fragments, and the sterile cultivars are not sterile.

Everything hard about this plant follows from its seed. One mature crown produces on the order of two to three million seeds per season. Each seed is roughly the size of a grain of dust, which means it moves in ways larger seed cannot: it floats and drifts on flowing water, it sticks in mud on boots, tires, waders, boat trailers and hooves, and it rides in the feathers and feet of waterfowl between wetlands that share no watercourse at all. In wet sediment it stays viable for several years, and often much longer. That is why control is measured in years after the last visible plant is gone, and why an infestation upstream is your problem regardless of what you do on your own bank.

Vegetative spread matters less but is not zero. The woody root crown enlarges each year and can be broken apart into pieces that re-establish, and cut stems left lying on saturated ground can root at the nodes. This is why crowns and cut material get bagged rather than left, and why heavy machinery working a wet site can seed a whole ditch line with fragments.

Then there is the cultivar problem, which is worth stating plainly because it is still repeated in catalog copy. The named garden selections — 'Morden Pink', 'Morden Gleam', 'Dropmore Purple' and material sold as Lythrum virgatum — were introduced and marketed as sterile. Controlled crossing studies showed they are self-incompatible, not sterile: they set little seed alone, and abundant viable seed when pollinated by another cultivar or by any wild plant within bee range, which in practice is always. Their offspring are fully fertile. This is why most state noxious-weed statutes list the whole genus rather than L. salicaria alone, and why a nursery tag reading “sterile” should be treated as a warning label rather than a reassurance.

Control, not care. A few plants: dig the whole crown before flowering and bag it. A wet meadow: the Galerucella leaf beetles, a biocontrol program that has actually worked. Any herbicide near water needs an aquatic-labelled product and usually a permit or a licensed applicator.

Scale decides the method. For a handful of plants — a garden clump, a few escapes along a ditch — dig out the entire woody root crown with a spade before it flowers, taking the crown intact rather than snapping the tops off. Disturb the surrounding soil as little as possible, because bare wet mud is an ideal seedbed for seed already banked there. Bag the crowns and any cut stems for the trash. Do not compost them, do not leave them on damp ground, and check the same spot for the next several years.

For anything larger, the honest answer is that hand removal does not scale, and the tool that does is biological control. Four European insects were screened and approved for release in the US from 1992: two leaf-feeding beetles, Galerucella calmariensis and G. pusilla, a root-boring weevil, Hylobius transversovittatus, and a flower-feeding weevil, Nanophyes marmoratus. The Galerucella beetles are the workhorses: they defoliate the plant repeatedly, and across many northern wetlands they have reduced loosestrife cover dramatically over roughly three to ten years, letting cattail, sedge and native forbs return. Biocontrol does not eradicate the plant — beetle and loosestrife populations settle into a cycle — but it converts a monoculture back into a mixed marsh, which is the actual goal. Releases are coordinated through state natural-resource agencies, county weed boards and extension offices, which often supply beetles free or run rearing programs volunteers can join. Ask in winter; summer release slots fill.

If you use herbicide, the rules near water are not optional. Use a product whose label lists aquatic sites — ordinary garden formulations are not legal to apply to or over water, and their surfactants are toxic to aquatic life. In most states, application in, over or immediately adjacent to water also requires a permit, a licensed applicator, or both; check with your state environmental or natural-resources agency before you buy anything. Follow the label rates, buffers, protective equipment and re-entry intervals exactly: the label is legally binding. Practically, treatment is usually spot application at bud to early bloom or in late summer as the plant moves resources downward, applied to individual plants with a wick or a targeted spray so the surrounding native vegetation survives — broadcast spraying a marsh just clears ground for the seed bank.

Whatever method you use, replant and re-check. Native wetland perennials that fill the same niche and the same visual role include blue vervain, swamp milkweed, Joe Pye weed, cardinal flower, ironweed, blazing star, boneset, buttonbush and native sedges and rushes. And clean your gear: hose boots, tools, tires and trailers before leaving a stand, and always work from clean ground toward infested ground rather than the reverse.

Not a food. The honest counterargument to removing it is that bees work it heavily - and it is worth answering directly, because the wildlife accounting overall is strongly negative: it replaces the marsh structure that muskrats, marsh birds and waterfowl actually depend on.

Purple loosestrife is not grown or gathered for food. The wildlife question is more interesting, because there is a real argument on the other side and it deserves a straight answer rather than dismissal.

The argument is that bees love it. They do. It is a heavy nectar producer over a long midsummer bloom, and nineteenth-century beekeepers deliberately planted it — loosestrife honey was a recognized crop. If your only measure is pounds of nectar per acre, it looks good.

The accounting that matters is broader. What loosestrife replaces is not bare ground; it is cattail, bulrush, sedge and wet-meadow plant communities, and those communities are the physical structure a marsh runs on. Muskrats eat and build with cattail and bulrush and largely will not use loosestrife. Marsh wrens, bitterns, rails and waterfowl nest in that structure. Native wetland forbs support specialist insects that in turn feed nestlings, and loosestrife supports very few — its own herbivores had to be imported deliberately. A dense loosestrife stand also traps sediment and reduces open water and channel flow, degrading habitat further and clogging irrigation ditches and drainage. So the trade is a long nectar flow for generalist pollinators against the loss of nearly everything else the wetland did.

If the nectar is what you value, the replacement list is easy and better: swamp milkweed, Joe Pye weed, boneset, blue vervain, ironweed, blazing star, buttonbush and cardinal flower bloom across the same window, feed the same bees, and additionally host the specialist insects and hummingbirds that loosestrife does not.

Answers for the reader with magenta spikes in a ditch: is this the noxious one or a native, is my garden cultivar really sterile, can I spray next to the pond, where do I get the beetles, and how long does this take.

Is this purple loosestrife? Square-ish four- to six-sided stems, stalkless lance-shaped leaves in opposite pairs or whorls clasping the stem, and a dense magenta terminal spike six to eighteen inches long from June to September, on a plant three to seven feet tall in wet ground. How do I know it is not a native? The one to be careful with is winged loosestrife (Lythrum alatum), a native: it is smaller, its upper leaves are alternate, and its flowers sit singly in the leaf axils rather than in a dense spike. Blue vervain has a branched candelabra of thin spikes and stalked toothed leaves. Fireweed has alternate leaves and four petals. Yellow and gooseneck loosestrife are Lysimachia and unrelated. Mine is a named garden variety sold as sterile: it is not sterile. 'Morden Pink', 'Dropmore Purple', 'Morden Gleam' and Lythrum virgatum are self-incompatible, not sterile, and set abundant viable seed when pollinated by any other cultivar or wild plant nearby. Most states list the whole genus for exactly this reason. Is it actually illegal? In most states, yes — planting, selling and transporting it are prohibited under the state noxious-weed law, and some states also require landowners to control it. Check your state's noxious-weed list. Can I spray it next to my pond? Only with a product whose label lists aquatic sites, and in most states only with a permit, a licensed applicator, or both. Garden herbicide formulations are not legal for application to or over water and their surfactants harm aquatic life. Call your state environmental or natural-resources agency first. Can I just pull it? For a few plants, dig the whole woody crown before it flowers and bag it; pulling the tops off achieves nothing. For a marsh, no — ask about beetles. Where do I get the beetles? Through your state natural-resources agency, county weed board or extension office; many run Galerucella rearing and release programs, often free, with releases in early summer. Ask in winter. Mowing? Do not mow a seeding stand — it scatters seed and chops crowns into propagules. How long does this take? Years. The seed bank persists in wet sediment long after the last plant is gone, so plan on re-checking a cleared site each year for at least five, and on biocontrol taking three to ten years to turn a large stand. What should I plant instead? Swamp milkweed, Joe Pye weed, blue vervain, cardinal flower, ironweed, blazing star, boneset, buttonbush, or native sedges and rushes.

Arrived in northeastern ports in the early 1800s in ship ballast and as a garden and bee plant, spread inland along canals and railways, exploded through the twentieth century, and became the subject of one of the largest and most successful biological control programs in North America.

Purple loosestrife reached the northeastern United States in the early 1800s by two routes at once: as seed in the soil and sand ballast dumped by European ships, and deliberately, as a hardy ornamental and a bee plant — loosestrife honey was a recognized crop and beekeepers planted it on purpose. It also travelled as a medicinal herb; European herbals had used it as an astringent for centuries.

From the coastal marshes it moved inland along exactly the corridors nineteenth-century America was building: canals, and then railways, both of which created continuous wet, disturbed ground and moved soil and water between watersheds. It was established across the Northeast by the 1830s, through the Great Lakes by the early twentieth century, and after mid-century it expanded explosively — helped by wetland drainage and disturbance, by roadside ditching, and by continued sale as a garden perennial.

By the 1980s it was one of the most-cited invasive plants in North America, and the response became a landmark. Rather than accept permanent chemical management of thousands of wetlands, agencies funded a long biological control program: European insects that feed on loosestrife were collected, screened for years against native plants to make sure they would not switch hosts, and the first releases were approved in 1992. The Galerucella leaf beetles established widely and, over the following decades, reduced loosestrife across large areas of the northern states and Canada while native marsh vegetation returned. It is one of the clearest successes in weed biocontrol — and a reminder that the reason the plant needed it at all is that a beautiful, tough, generous garden perennial from one continent can be a catastrophe on another.

Established in nearly every state and hardy to about zone 3, with the heaviest impacts across the northern tier - the Northeast, Great Lakes, upper Midwest and Pacific Northwest. In the arid West it concentrates in irrigation ditches and river corridors, where it is regulated hardest.

Purple loosestrife is hardy to roughly zone 3 and grows through about zone 9, and it is recorded in nearly every US state and much of Canada. Its heaviest impacts fall across the northern tier: New England and the mid-Atlantic, the Great Lakes basin, the upper Midwest, the northern plains and the Pacific Northwest, where cool summers, abundant wetlands and a long history of introduction line up. Minnesota, Wisconsin, Michigan, New York and Washington all run long-standing control and biocontrol programs against it.

In the arid West and Intermountain states it behaves differently but is treated even more severely. Water there is confined to river corridors, irrigation canals, ditches and reservoir margins, so the plant concentrates in exactly the infrastructure that agriculture depends on, where dense stands slow flow and clog delivery. Western and plains states generally list it as a noxious weed with mandatory landowner control duties, and county weed boards actively enforce it.

Two practical consequences. First, work upstream: seed moves with water, so a stand at the top of a drainage reseeds everything cleared below it, and coordinating along a whole watercourse beats working one bank. Second, in the far south and southwest, where it is scattered rather than dominant, a new plant is a genuine emergency worth reporting to the state agriculture or natural-resources department — early detection and rapid response on a handful of plants is a hundred times cheaper than anything available once a stand establishes.