I am happy to welcome back my Minnesota Master Naturalist colleague, Steve Dietz. Steve is an amazing bird watcher and a very active and enthusiastic member/leader of the Frontenac State Park Association. As an avid birder, when not enjoying the dawn chorus, he is working to enhance FSP's bird-friendly habitat and resources. I loved reading this thoughtful article on how we think about weeds and how, what at first seems to be an invasive, is actually a native species that plays an integral part in out natural ecosystems. You'll see the humble field thistle with different eyes after you read his piece.
Notes from the Field: A Weed is a Weed is a Weed?
by Steve Dietz
Reprinted by permisssion from the Frontenac State Park Association newsletter, August 2026
Many of us feel that “weed” is an immutable category that must be extirpated at all costs, including killing off beneficial flora and fauna. But don’t worry, we are not diving into lawn wars this month. It’s useful, however, to understand weeds as a cultural construct. Most programs and experts, when pressed, define weeds along these lines: a wild plant growing where it is not wanted, especially among crops or garden plants. On a tour of He Mni Can, Nicky Buck, a member of the Prairie Island Indian Community, referred to so-called invasive species as “misplaced relatives.”
Don’t get me wrong. A weed can cause severe damage to agricultural output, hence the Minnesota Department of Agriculture’s noxious weed list. And very few of us really love creeping charlie inundating our cultivated gardens. But in the wild environment of Frontenac State Park, what is a wild plant growing where it is not wanted — besides buckthorn and garlic mustard and wild parsnip? Of course, the argument that these should be at least controlled if not eradicated is based on the fact that they aggressively take territory and prevent the growth of native flora that have evolved over millennia to support a host of dependent native insects, birds and mammals.
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| Left: A monarch butterfly nectaring on a field thistle, Frontenac State Park, August 30, 2021. Photo bysls42, iNaturalist. Right: An American Goldfinch eating thistle seed. Photo by Steve Dietz |
Often in the prairie, especially in August, I come across a butterfly feeding on a thistle in purple bloom. Beautiful! Somewhere inside me, however, is some unformed concern about a weed in the prairie. Did I not wipe my boots and accidentally bring it to the trail on a past walk? Perhaps. I do not know where this association of thistles with weeds first arose, but in this case the concern is specious. Or should that be species-ist?
The field or pasture thistle (Cirsium discolor) is a native plant that is a prodigious food source. The most important pollinators of the flowers are bumblebees, digger bees, leaf-cutting bees and butterflies. Among the butterflies are such floral visitors as Monarchs, Fritillaries, Painted Ladies, Swallowtails and Sulfurs. Sphinx moths and bee flies also visit the flowers for nectar. The caterpillars of the Painted Lady butterfly and several moths feed on the foliage., Other insect feeders include the Thistle Tortoise Beetle, the Bumble Flower Beetle, the Thistle and Artichoke aphids, the Northern Grasshopper and many others. The American Goldfinch eats the seeds and uses the tufts of hair as lining material in its nests, and the Ruby-throated Hummingbird has been known to visit thistle flowers for nectar.
The USDA also cites uses of the field thistle by Native Americans, who made a paste of the roots for treating wounds, boils and piles, and used an infusion of the root for treating stomachaches. Some also used the thistle down (or pappus) from the seeds to fletch the tail end of blow darts.
The field thistle can be confused with the bull thistle (Cirsium vulgare), an aggressive non-native species. The way to tell them apart visually is that bull thistle has leaves that are green on both sides. Field thistle leaves have white underneath and spineless stems. The former blooms in spring; the latter blooms summer into fall.
Interestingly, while both native and non-native thistles provide useful eco services, the aggressive territoriality of non-native species puts them in the “growing where not wanted” category, although probably not enough to need additional control measures at the park.
“Maintaining” a natural environment is a complex and sometimes contradictory endeavor, and the answers are not always obvious. Question assumptions. Become informed about the life cycle and eco and cultural services of a plant. Consider what is acceptable and practical in your unique circumstances. Be humble.
The field or pasture thistle (Cirsium discolor) is a native plant that is a prodigious food source. The most important pollinators of the flowers are bumblebees, digger bees, leaf-cutting bees and butterflies. Among the butterflies are such floral visitors as Monarchs, Fritillaries, Painted Ladies, Swallowtails and Sulfurs. Sphinx moths and bee flies also visit the flowers for nectar. The caterpillars of the Painted Lady butterfly and several moths feed on the foliage., Other insect feeders include the Thistle Tortoise Beetle, the Bumble Flower Beetle, the Thistle and Artichoke aphids, the Northern Grasshopper and many others. The American Goldfinch eats the seeds and uses the tufts of hair as lining material in its nests, and the Ruby-throated Hummingbird has been known to visit thistle flowers for nectar.
The USDA also cites uses of the field thistle by Native Americans, who made a paste of the roots for treating wounds, boils and piles, and used an infusion of the root for treating stomachaches. Some also used the thistle down (or pappus) from the seeds to fletch the tail end of blow darts.
The field thistle can be confused with the bull thistle (Cirsium vulgare), an aggressive non-native species. The way to tell them apart visually is that bull thistle has leaves that are green on both sides. Field thistle leaves have white underneath and spineless stems. The former blooms in spring; the latter blooms summer into fall.
Interestingly, while both native and non-native thistles provide useful eco services, the aggressive territoriality of non-native species puts them in the “growing where not wanted” category, although probably not enough to need additional control measures at the park.
“Maintaining” a natural environment is a complex and sometimes contradictory endeavor, and the answers are not always obvious. Question assumptions. Become informed about the life cycle and eco and cultural services of a plant. Consider what is acceptable and practical in your unique circumstances. Be humble.
