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Cirsium discolor (Field Thistle), together with Cirsium muticum (Swamp Thistle), is Floyd County’s native thistle, and a staple of any butterfly garden. Thistle is wreathed in lore, appearing in heraldry since ancient times, and persisting into the modern era as logo and crest. Thistles tend to thrive in anthropogenic (human-made) disturbance, which might in part explain its presence in the agrarian imagination, faded though that presence has become in the modern era. But the mystique of thistle seems to extend beyond this. Might thistle’s ecological importance be a part of its mystique? It is true that native thistles are ecologically important enough that the Xerces Society created a book-length guide on the topic that includes extensive propagation information: Native Thistles: A Conservation Practitioner’s Guide.
An Old World Aesthetic
Thistles are not traditionally grown in ornamental gardens, though they were certainly present in Medieval gardens. Planting them in your butterfly and flower gardens requires perhaps an Old World aesthetic, or a different kind of eye. They do grow rather tall with spines and fade to brown by late summer or early fall to create an imposing prickly presence in the fall and winter garden. But if you enjoy the butterflies and birds they attract, that is a different kind of beauty!
An Easy Biennial
Cirsium discolor can be grown in most any sunny mesic cultivated garden, though it is a widely adapted pioneer species able to scrape out a living in many disturbed or subxeric habitats. Across the state of Virginia, it can be found in “floodplain forests, mesic to dry upland forests and woodlands, clearings, old fields, meadows, and roadsides” (Digital Atlas of the Virginia Flora). Usually grows as a biennial (living only two years) or a short-lived perennial. It does not spread by rhizome but by seed which it produces right before dying. As a result, if you decide you don’t want to continue growing Cirsium discolor, cut the flowers before they go to seed or remove the seedheads before they are dispersed. You’ll want to make sure you beat the birds to the seeds, or they’ll help spread it around!
Sadly, Cirsium discolor has been targeted for eradication largely due to the invasive behavior of its non-native cousins, the European Bull Thistle (Cirsium vulgare) and Canada Thistle (Cirsium arvense) which, despite the name, is not native to North America. Cirsium discolor can be distinguished from non-native thistles by the white woolly undersides of the leaves which none of the non-native thistles have and all North America’s native thistles do have. It also has fewer spines and less aggressive growth.
If you want to keep it around your garden, you may be able to simply let it self seed and, in the spring, transplant or weed out poorly located seedlings. Do this early, before the long taproot develops. You can increase reseeding rates by gathering and planting seeds in the fall near the parent plants or in other likely locations once temperatures cool. You can also collect and store seeds in a cool dry place, then cold moist stratify in a bag of damp sand in the fridge for two months before planting in spring. Due to its taproot, containers should be at least 5″ deep. Refer to Xerces Society’s Native Thistles: A Conservation Practitioner’s Guide for more information on cultivation.
“The young leaves and stems are edible after boiling. Native Americans used the roots to make poultices for treating wounds and boils.” (Go Botany Native Plant Trust, 2023)
A Butterfly Garden Champion
Native thistles attract many butterflies (including the monarch butterfly) with their copious nectar. Cirsium discolor is noted of Special Value to Native Bees by the Xerces Society (Wildflower.org), as a keystone species for 15 species of native bees by Dr. Doug Tallamy, and as a provider of nesting habitat for some native bees including leaf miner bees which nest in the hollow stems (Xerces, 2017). The American goldfinch in particular loves the seeds, as do small mammals and insects. (U. S. Forest Service, 2023). Cirsium discolor is one of many other thistles and asters worldwide to host the Painted Lady butterfly (Vanessa cardui), a charismatic butterfly with a large migratory range (Wikipedia, 2023).