What is giant hogweed?

Giant hogweed is an enormous member of the carrot family that came to North America from the Caucasus as a garden novelty. Good giant hogweed identification matters because this plant is a real health hazard, not just an eyesore. Its sap can leave you with burns and blisters that look like a bad scald.

The plant lives for several years as a big leafy rosette, then sends up a towering flower stalk, drops thousands of seeds, and dies. Those seeds can lie in the soil for years, which is why one plant in a ditch can turn into a patch along a whole stretch of creek.

Pennsylvania lists giant hogweed as a Class A noxious weed, and it’s on the federal noxious weed list too. It’s illegal to sell, move or plant it in the state, and the PA Department of Agriculture actively works to find and eliminate it.

Giant hogweed identification: what to look for

Size is the first clue. A flowering giant hogweed is usually 8 to 14 feet tall, so it stands well above a grown adult. Lots of plants in the carrot family have white umbrella-shaped flowers, though, so check several features before you decide.

• Stem: hollow, ridged and thick, often 2 to 4 inches across, with purple-red blotches and coarse white bristly hairs, especially where leaf stalks join the stem.
• Leaves: huge, deeply cut and lobed, sometimes 5 feet wide, with stiff hairs underneath.
• Flowers: many tiny white flowers in a flat-topped cluster that can reach 2½ feet across, usually in June and July.
• Seeds: flat, oval and tan with brown stripes, ripening in late summer.
• After flowering: the plant dies, but the dry stalks often stay standing into winter.

Look from a distance and take photos instead of handling anything. You can make an ID without getting close enough to brush against it.

Where it grows in Pennsylvania

Giant hogweed has turned up at scattered sites across Pennsylvania. It likes moist, rich ground and partial sun, so the usual spots are stream banks, drainage ditches, roadside swales, woods edges and the yards of old homes where someone planted it years ago.

Because seeds float, a single plant upstream can seed in along a creek for a long way. In our river valleys and wet hollows, that’s the pattern to watch for: plants along the water’s edge rather than in the middle of a mowed lawn.

Giant hogweed look-alikes

Most of the big white-flowered plants you’ll see in central PA aren’t giant hogweed. The most common mix-up is native cow parsnip, which is shorter, has a thinner green stem with soft fuzzy hairs, and blooms a few weeks earlier.

Poison hemlock has smooth purple-spotted stems and lacy, fern-like leaves, and it’s dangerous in its own way because every part is poisonous if eaten. Wild parsnip has yellow flowers but its sap causes the same sun-triggered burns. Angelica and Queen Anne’s lace are much smaller and far less hazardous. When in doubt, treat the plant as hazardous and let the state make the call.

How to get rid of giant hogweed

This is one weed you should not take on yourself. Cutting, mowing or string-trimming sprays sap around, puts you at risk, and the plant simply regrows from its root. Digging it out without proper protective gear is just as risky.

1. Keep people and pets away. Tell family members, and don’t let kids play near it.
2. Take photos from a safe distance. Get the whole plant, the stem and a leaf if you can.
3. Call the Giant Hogweed Hotline at 1-877-464-9333. The PA Department of Agriculture will confirm the ID and work with you on how the site will be managed.
4. Leave it alone in the meantime. Don’t cut seed heads, don’t move dried stalks, and never share seeds or plants.

State and federal crews use herbicide treatments that are known to work on this plant and then check back for seedlings. If herbicide is part of the plan, it must be a product labeled for the site, applied according to the label, and anyone applying herbicide for hire in Pennsylvania needs a PA Department of Agriculture pesticide applicator certification. Near streams, only products labeled for use near water can be used.

Expect this to take several years. Seeds in the soil keep sprouting, so follow-up visits are part of the job.

Keeping it from coming back

Once a site is treated, the goal is to stop any new plant from ever flowering again. Walk the area each spring and early summer and watch for new rosettes with deeply cut, hairy leaves, especially along the water’s edge.

Report any new plants to the hotline rather than pulling them yourself. After the state signs off that the patch is under control, getting the ground covered with a healthy stand of grass or native plants helps crowd out seedlings, but don’t start regrading or moving soil from the area until you’ve talked with the people managing the site, since soil can carry seed to a new spot.

Questions we get about giant hogweed

Similar weeds

Wild ParsnipPastinaca sativaPoison HemlockConium maculatumQueen Anne's Lace (Wild Carrot)Daucus carota