How to Identify Giant Hogweed, the Plant That Can Cause Severe Burns and Blisters

Giant hogweed is a plant that can cause severe burns and blisters. Its pretty looks earned it a spot as an ornamental plant through the 1800s, leading to its spread from its native Eurasia to Europe and North America.

Giant hogweed is now a bona fide invasive species, choking out native species along Europe and North America. It is especially prevalent along riverbanks and in disturbed ecosystems. Identifying giant hogweed is the first step to avoiding it and removing it.

How to Identify Giant Hogweed

Giant hogweed is also known as cartwheel flower, giant cow parsnip, hogsbane, and giant cow parsley. It’s important to be able to identify this dangerous plant.

Giant hogweed looks quite a bit like several other plants, including cow parsnip, Purplestem angelica, woodland angelica, valerian, lovage, and Queen Anne’s Lace. However, none of these other plants are anywhere near as large as a mature giant hogweed plant.

Cow parsnip and wild parsnip both have similarly dangerous sap. In parts of Canada, cow parsnip is considered rare and should not be removed unless it’s posing a threat.

Aside from its size, giant hogweed can be separated from its lookalikes thanks to the purplish-red spots on its stem paired with coarse bristles. Some lookalikes have fine hairs or reddish spots, but none of the lookalikes have both.

Giant Hogweed Identification
Height2-5.5 meters (6.5 – 18 ft)
Leaf Size1 – 1.7 meters (3 – 5.5 ft) across
Leaf ShapeRoughly triangular with three large lobes, each deeply lobed as well. Edges are spikey and serrated.
FlowersNumerous small white flowers arranged in umbrella-shaped heads up to 80cm (31 inches) across. Flowers in late spring to mid summer.
StemThick, bright green often with reddish spots – can also be nearly completely reddish. Covered in sturdy white bristles. Stems are hollow and are 3 – 8 cm (1 – 3 inches) in diameter.

What Happens if You Touch Giant Hogweed?

If you accidentally touch giant hogweed, you should immediately wash your hands with cold water and keep your skin out of sunlight. Use sunscreen, even if you’re inside, on the affected area. Many windows do not block enough UV light to keep you safe if you touch giant hogweed.

The sap of giant hogweed is incredibly phototoxic, meaning it causes severe inflammation if you get the sap onto your skin and then expose your skin to sunlight. If your skin comes in contact with the watery sap of giant hogweed, you will experience:

  • Reddish skin and itching within a few hours.
  • Blister formation within 48 hours of exposure.
  • Black or purple scarring from the blisters that will last several years.

In severe cases, hospitalization is necessary. For obvious reasons, governments around the world support aggressive measures to eradicate giant hogweed.

In fact, the government of Ontario put together a whole e-book on giant hogweed. Scroll to page 6 to see the damage that exposure to giant hogweed can do – skip this if you’re squeamish.

How to Remove Giant Hogweed

If you find giant hogweed on your property and want to remove it, your best bet is to hire a professional. Working with a professional will ensure that you stay safe and that the job gets done right.

If you can’t find (or can’t afford) a professional, removing giant hogweed is a big endeavor:

  1. If possible, you should wear a disposable “spray suit” commercial grade waterproof coveralls over all of your normal clothes. Wear waterproof gloves, eye protection, and long sleeves.
  2. Herbicides are a good way to control the top growth of giant hogweed – especially glyphosate. You will need to re-apply glyphosate in following years, as it does not kill roots and plants will still produce new seedlings.
    • If the giant hogweed has flowers with unripe seeds (seeds are white and not green), remove flower heads and place them in black plastic bags. Do not burn them and do not compost them. Check with your local officials to see if you can dispose of giant hogweed at the local landfill.
  3. Manual removal is incredibly difficult without professional help due to deep roots and heavy potential re-seeding. Giant hogweed can resprout from roots.
  4. When you’re done, remove and wash your rubber gloves with soap and water. Then use them to remove your spray suit, and wash the gloves again. Remove your eyewear with clean gloves. Put non-disposable clothing in the laundry and take a shower. Put disposable clothing into black plastic bags for disposal. Do not burn disposable clothing. Be careful to avoid getting any sap onto your body.

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