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Weed of the Month: White Snakeroot

Fall-blooming white snakeroot is that nondescript weed that has been inconspicuously growing in shady spots all spring and summer. You barely notice the one- to four-foot-tall plant with toothy, dark green leaves until suddenly—poof! It’s everywhere you turn, all abloom with fluffy white flowers. One of the last wild natives to flower, Ageratina altissima is a godsend to hungry insects like bees, moths, and flies furiously foraging before the weather turns cold and food becomes scarce.

After blooming, its seeds are dispersed primarily by wind, their fuzzy tails carrying them far and wide. The plant also spreads by rhizomes (underground stems), so you’re as likely to see a colony as a single specimen. Originally a woodland plant, white snakeroot is also perfectly at home in the sidewalks, vacant lots, and shady gardens of Brooklyn.

Sadly, white snakeroot played an unfortunate role in American history. In the early 19th century, European settlers, unfamiliar with the plant, allowed cows and other domestic animals to feed on it. A toxin in the plant called tremetol tainted the cow’s milk, causing sickness and death to those who drank it, calves as well as humans. Milk sickness, as it was called, claimed the lives of thousands of people, including, it is thought, Abraham Lincoln’s mother. Native Americans, who made poultices with snakeroot, knew of its toxic properties, but their botanical knowledge was frequently overlooked by settlers, to their detriment.

Eventually, a frontier doctor in Illinois named Anna Pierce Hobbs Bixby learned of the cause of the sickness from a Shawnee medicine woman. Bixby helped control the disease locally by instructing settlers to remove white snakeroot from their fields, but she too was largely ignored by the medical community, and research confirming the connection between snakeroot and milk was only published much later. Today, for better or worse, industrial agriculture has all but eradicated milk sickness. Since milk from thousands of cows is now combined when processed, the occasional toxin-containing contribution would be diluted to harmless levels.

White snakeroot is most easily identifiable in the fall, when its fluffy white flower heads appear, but it has another distinctive characteristic that appears when it leafs out in spring. Look for elaborate, curving trails on some leaves. These are the work of a species of fly (Liriomyza eupatoriella) that makes white snakeroot its host. The fly lays its eggs on the leaf, and after they hatch, the larvae feed on the leaf tissue, tunneling their way around and creating the beautiful, albeit destructive patterns. Vegetable gardeners may recognize these patterns as the telltale sign of leaf miners that attack their chard, beet, spinach, and tomato plants in much the same way. The intricate tunnels don't do these plants any good, though white snakeroot seems better able to tolerate them than some other species. Another wondrous peek into the complexities of nature: The same plant that could kill a cow is baby food for a tiny fly!

The Weed of the Month series explores the ecology and history of the common wild plants that most gardeners consider weeds.

Saara Nafici is the executive director of Added Value/Red Hook Community Farm. She is also the former coordinator of the Garden Apprentice Program at Brooklyn Botanic Garden and a longtime activist, feminist, bicyclist, naturalist, and youth educator. Follow her weedy plant adventures on Instagram.

    Discussion

  • Joe July 7, 2020

    Snakeroot is taking over my two acre goat pasture, partly wooded, partly grassy. The snakeroot indeed thrives in shade. The goats avoid it so it’s been proliferating like mad over the last 15 years. I’d love to eradicate it — it’s now spreading to flower beds around the house—but I give up!

  • Kat May 10, 2020

    Roy, this is NOT the herb that is used medicinally! This plant, Ageratina altissima, white snakeroot, is deadly, as the author describes in the article. Aristolochia serpentaria, sometimes called Virginia snakeroot, has been used medicinally but is also very toxic if used in the wrong way and at the wrong dose. They are unrelated, and are in different plant families. There are other “snakeroots” with claims to medicinal properties as well. I don’t know which one might be sold at farmer’s markets.

    This is a perfect example of common names causing confusion, and one should be very careful to use Latin names to identify a plant before consuming. Most plants have more than one common name, often many, and most common names can refer to more than one plant.

    Alice, you ask if goats can safely eat it. As a retired vet, I say if it kills cows and horses, I wouldn’t let my animals near it! Even if they aren’t affected by it, their milk will likely contain the toxins, so shouldn’t be consumed.

  • Jackie Bennett November 11, 2019

    Like Laurie (above), I never saw it until this Fall at my house on Staten Island.  I am thrilled.  At first I worried and worried that it was another invasive (I do daily battle with vines), but I think it is native and I am so happy.  Soothes my nature-loving conscience.  Now I am wondering as the flowers fade if it is okay for me to cut it back to the ground - I don’t want to kill it.  I want it to grow and spread next year.

  • Laurie November 7, 2019

    I too had never seen it around my house on Long Island until this year…and this spring and summer seemed to be taking over everything!  But I too am glad it’s a native and servers a purpose in the fall.

  • ALICE October 15, 2019

    At the community farm where I volunteer we have white snakeroot, and, we have goats who help with some of our ‘weeding’. Is this also poisonous to goats, I wonder?

  • Diane Brancato October 4, 2019

    I’ve never had it before in my garden, and it’s all over the place. It is dangerous to handle this plant.?  I have loads of blue ageratum and thought this must be in the same family.

  • Laurie September 25, 2019

    If the toxin is transferred to cows milk and poisonous to humans ....will honey be okay if the honeybees are enjoying snakeroot now?

  • Ilene September 21, 2019

    I have them blooming allllll over my woods. Pretty though.

  • Roy August 18, 2019

    A weed that is worth over $100/lb at some farmers markets.

  • Clark Allworth November 5, 2016

    As a visitor from the West Coast, I was very pleased to see the information about this plant, which I have seen everywhere in the parks around here. This is a great idea to feature a weed of the month; please continue doing so! And I hope to visit the garden soon!

  • Tracy LaBar October 21, 2016

    Thank you for the great information! I have several books published by BBG, and I was thrilled to see your “Weed of the Month” the snakeroot plant. I didn’t know what it was; they are all over my yard!! I’m glad to hear they are a native and helpful to many insects :) Continued success and provision of great information.

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