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Giant Hogweed: Put on Your Hazmat Suit before You Go Outside

Have you heard the one about the mammoth carrot plant that’s so toxic it can scar your skin and permanently blind you? It’s the Giant Hogweed (Heracleum mantegazzianum), a plant indigenous to Caucasus and Central Asia that was imported to Europe in the 19th century as a showy perennial and then made its way to North America.

It looks like Queen Anne’s Lace that got tasered with a nuclear beam:

Evil in bloom.

Today it can be found throughout the temperate portions of Canada and the American Midwest, Northeast, and Pacific Northwest:


Sorry, Canada.

The giant hogweed lives up to its name: It’s a weed that grows up to 14 feet tall with leaves that can span 5 feet wide and white flower clusters up to 2.5 feet in diameter. And like a giant hog it can hurt you if you get too close. That’s because it is phototoxic, meaning that if the plant’s sap comes into contact with your skin and then your skin is exposed to sunlight, your skin will become discolored and then blister (this process is called phytophotodermatitis).

Gloves in the garden—always a good idea.

The reaction can start up to 48 hours after contact. In some cases, the blisters can cause permanent scarring and discoloration. What’s more, if you get the sap on your fingers and then rub your eyes, you can go blind—either temporarily or permanently. This is a problem, given that children “have been known to use the plant’s large, hollow stems as play telescopes or pea-shooters,” according to Drew Halfnight, writing in Canada’s National Post. Way to ruin your weekend.

Giant Hogweed is more dangerous than poisons ivy, oak, and sumac. So it makes sense that you learn how to identify it. You don’t want to be the one wrapping your bare arms around the stalk saying, “Hey, George, would you look at the size of this thing?”

By gum, it's taller 'n LeBron James.

Luckily, it’s not hard to spot when it’s fully grown—its size is a huge clue. First off, you’re probably safe on the golf course, the beach, and the neighborhood tot lot. Like poison ivy, Giant Hogweed thrives in disturbed environments; areas along roadways, waterways, and the edges of wooded areas where civilization meets up with the wild. Apart from its height, the other giant thing about the plant is its leaves, which are lacy and compound, like 5-foot wide fronds of celery or carrot greenery (they belong to the same family). The hogweed’s flower clusters are comprised of many tiny flowers on umbrella-like stems that can span over a foot.


The real problem is identifying the plant before it blooms and before it reaches its leviathan size; the Giant Hogweed can take up to four years to reach maturity. And when it does bloom, each flower head can release 50,000 seeds, which can stick around in the soil for a few years. So really, don’t even think of leaving home without protective clothing.

Innocent? I think not.

For more pictures of the Giant Hogweed in various states of growth, see here.

It’s a perennial, meaning that unless you dig out the entire root system, it will grow back the next year. Just make sure you’re wearing your hazmat suit (or long sleeves, pants, and rubber gloves). Let the plant rot in the sun. Make sure the seeds don’t spread by putting the flower head in a big ol’ plastic bag and letting that rot in the sun too. Prevent seeds from sprouting by covering the area in plastic. Spraying with repeated applications of glyphosate (the active chemical in Roundup) also works, just make sure you’re getting those dangnabit seedlings that are bound to pop up in the spring. Or, better yet, just call your local university extension or department of natural resources and have them take care of it.

Mother Nature is out to get you.

One problem in identifying Giant Hogweed is that its primary doppelganger is the nontoxic cow parsnip, with the primary differences being that of size. Of course, making this distinction may be difficult if you’re looking at a giant hogweed that’s still growing. A cow parsnip leaf only grows up to 2.5 feet wide and its similar-looking flower clusters only grow to 1-foot wide. Cow parsnip is actually useful;  Native Americans have used it for centuries as a natural insect repellant.

Cow parsnip: A good plant.

The Giant Hogweed has the rare distinction of having been confirmed on as really living up to its hype, rather than debunked as a hoax like the latest celebrity death rumor. However, other media outlets are trying to stem (heh) the hysteria. The Michigan State University Extension wants people to know that you’re not likely to see the plant on “a vigorous tramp through the woods or wetlands.” But it’s always a good idea to remember that plants can be evil.

So let’s review what we need to stay away from as we go cavorting through the field chasing butterflies this summer. Always be on the lookout for that nasty trio that can ruin your adventure:


Trifecta of killjoy foliage.

For poison oak and poison ivy, don’t forget: “Leaves of three, let them be.” For sumac, remember: “Leaves of nine, very bad sign.”

How about this for the Giant Hogweed: “Mammoth Queen Anne’s Lace—shield your hands and face, and call the hazmat team posthaste.”

Kathy Wilson Peacock is a writer, editor, nature lover, and flaneur of the zeitgeist. She favors science over superstition and believes that knowledge is the best super power. Favorite secret weapon: A library card.

Posted on: July 22, 2014, 6:00 am Category: Current Issues Tagged with: , , , ,

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