Giant Hogweed

A 14-foot Caucasian umbel with a purple-blotched, white-bristled stem and a flower head the width of a car tyre. Its sap plus sunlight causes burns that blister, scar and leave skin sun-sensitive for years, and it can blind. It is a federal noxious weed: identify it, stay off it, and report it.

Recognition, not cultivation. Four features checked together: 8-14 ft height, a hollow 2-4 inch stem with sharp purple blotches and coarse white bristles, jagged leaves up to 5 ft, and a white umbel up to 2.5 ft across. Nearly every false report turns out to be cow parsnip.

You never grow this plant. What follows is how to be sure, because most reports of giant hogweed turn out to be one of five commoner plants — and because a confident identification is what gets a state crew to come out.

The four features, checked together. No single one is enough on its own. (1) Size: a flowering plant is 8 to 14 feet, occasionally taller, and simply looks wrong for anything else growing in a ditch. (2) Stem: hollow, ridged, two to four inches thick, marked with sharply defined dark purple-red blotches and streaks, and clothed in coarse, stiff white bristles that are thickest at the base of each leaf stalk. (3) Leaves: up to five feet wide, deeply incised into sharply pointed, jagged lobes, with stiff bristles under the midrib. (4) Flower head: a flat white umbel up to two and a half feet across, carrying 50 or more spokes, in June and July.

Against cow parsnip (Heracleum maximum), which is native, common, and what almost every false report turns out to be. Cow parsnip is 4 to 8 feet, not 14. Its stem is one to two inches thick, ridged, and covered in fine soft fuzz rather than coarse bristles; it may flush purple, but not in the sharply defined blotches giant hogweed carries. Its leaves are broad and maple-like with rounded lobes, not jagged. Its umbels are 6 to 12 inches across, not two and a half feet. One important caveat: cow parsnip sap also causes phytophotodermatitis, just far less severely — so guessing wrong in this direction still means a plant to handle in gloves and sleeves, not a harmless one.

Against poison hemlock (Conium maculatum): hemlock reaches 6 to 10 feet, but its stem is smooth and completely hairless, spotted rather than blotched, and no thicker than a finger; its leaves are finely divided and ferny rather than huge and jagged; and it smells musty. Hemlock is a lethal poison if eaten but does not burn. See the 'poison-hemlock' entry.

Against wild parsnip (Pastinaca sativa): yellow umbels, 4 to 5 feet, a hairless grooved stem, broad celery-like leaflets. It burns by the same chemistry, far less severely. See the 'wild-parsnip' entry.

Against Queen Anne's lace: 2 to 4 feet, a solid hairy stem, ferny leaves, and a 3- to 5-inch umbel usually carrying one dark floret at the centre. Not remotely the same scale. See the 'queen-annes-lace' entry.

Against angelica and elderberry, both regularly reported: Angelica has a smooth purple stem and a rounded, globe-shaped flower head rather than a flat one; elderberry is a woody shrub with opposite compound leaves. Neither has a bristly, blotched stem.

One more, because it has hurt people: giant hogweed stalks have been cut and handled by adults who took them for wild rhubarb. Rhubarb leaves are huge but broadly heart-shaped with a wavy edge and no deep lobing, its stalks are smooth and unbristled, it never exceeds a few feet, and it does not carry an umbel at all. If a stalk that looks like rhubarb is attached to a jagged, deeply cut leaf on a bristly, purple-blotched stem, put it down and wash your hands.

There is no home control. Photograph it from a distance, report it to your state agriculture or invasive-species program, keep people and pets off it, and let a trained crew do the work - in most of its range that service is free.

The correct action is report, not remove. Giant hogweed is a federal noxious weed, and most states in its range run a reporting line and a control program — New York, Pennsylvania, Ohio, Michigan, Vermont, New Hampshire, Maine, Washington and Oregon among them. In many of them a state or county crew will come and treat the site, often at no cost to the landowner, and will return for the follow-up years that actually decide the outcome.

To report it: photograph the plant from a safe distance — whole plant, stem close-up, one leaf, and the flower head if present — note the location as precisely as you can, and contact your state department of agriculture or invasive species program. A good stem photograph is what separates a real find from the cow parsnip that most reports turn out to be.

Do not mow, strim, chip or burn it. A string trimmer aerosolises the sap directly onto your face and forearms and is the single most reliable way to be badly hurt by this plant. Chipping sprays it. Burning carries the same compounds in smoke. Mowing does not kill it either — it regrows from the crown.

While you wait for a crew, keep the area off-limits. Children are injured by this plant out of all proportion to their numbers, usually because a hollow stem makes an appealing telescope or pea-shooter and puts sap around the mouth and eyes. Mark or rope off the stand if you can do it without approaching, tell your neighbours, and keep pets away.

If no program exists where you are and a single plant must be dealt with, the standard method is root cutting: full waterproof coveralls, face shield and goggles, gloves taped to the sleeves, on a still, overcast day — sever the taproot 4 to 6 inches below the soil surface with a spade, bag the crown, and cut and bag any flower head before the seed sets. Remove the protective gear carefully afterwards and wash everything separately. Then expect to return: buried seed can stay viable for around a decade.

First aid in order: out of the sun, wash with soap and cold water, keep the skin covered from sunlight for 48 hours, and see a doctor for blisters. Sap in the eye needs immediate care. Any ingestion is an immediate poison-control call.

Sap has touched my skin. Do this now, before any rash appears. Get out of direct sunlight. Wash the area thoroughly with soap and cold water. Then keep that skin covered from sunlight for at least 48 hours — the burn only happens where UV light reaches the sap compounds, so shielding the skin during that window is the single most effective thing you can do. Wash any clothing, gloves and tools that touched the plant, separately from everything else.

Sap got in my eye. Rinse immediately with clean water and seek medical care at once, keeping the eye shielded from light on the way. Sap in the eye has caused temporary and, in some cases, permanent blindness — do not wait to see whether it hurts.

It has blistered. Expect redness at roughly 15 hours and blistering within 48. Do not break the blisters. Cover them, keep them out of the sun, and see a doctor — severe cases are managed as burns and may need prescription treatment. Afterwards the skin usually darkens for months, and can remain sun-sensitive for several years; keep that patch covered or under a high-factor sunscreen whenever you are outdoors.

A child was playing with the stems. Assume hands, face and eyes are all exposed. Wash all of them, keep the child indoors and out of sunlight, and seek medical advice the same day rather than waiting for a rash to appear.

Someone ate part of it. Call poison control or emergency services immediately, and do not wait for symptoms. Beyond this plant itself, this is a family that contains poison hemlock and water hemlock, both lethal and both growing in the same damp, disturbed ground — so any ingestion of a large white-umbelled plant is treated as an emergency until the species is confirmed. Take a photograph rather than a sample.

A pet or livestock got into it. Blistering occurs on muzzles, udders and thin-haired skin, and grazing animals can become photosensitised. Move animals off, keep them shaded, and call a vet about any blistering.

Am I sure it is not cow parsnip? If it is under 8 feet, the stem is under two inches thick with soft fuzz rather than coarse bristles, the purple is a general flush rather than sharp blotches, and the leaves are broad and maple-like rather than jagged, it is almost certainly cow parsnip — a native plant that still causes a milder version of the same burn. Report it anyway if you are unsure. State programs would far rather look at a photograph of a cow parsnip than miss a real one.

A Victorian ornamental import from the Caucasus, planted deliberately for spectacle, now a federally listed noxious weed with reporting hotlines and eradication crews in a dozen states.

Giant hogweed is native to the western Caucasus, in Georgia and southern Russia, where it grows in mountain meadows and along forest edges. In the early nineteenth century it was collected as an ornamental curiosity: British gardeners planted it for its architectural scale, seed was circulated through horticultural societies and seed exchanges, and it reached North America the same way, appearing in ornamental plantings from around the 1910s.

It escaped everywhere it was planted. A single flowering plant can set tens of thousands of seeds; the seeds float, so rivers carry them; and the species colonised riverbanks, roadsides and waste ground across Britain, northern Europe, southern Canada and the northeastern United States. By the late twentieth century the injuries were documented well enough that regulators acted. It went onto the US Federal Noxious Weed List, making it illegal to import, sell or transport across state lines, and states from New York to Washington set up reporting hotlines and eradication crews. Britain went further and made it an offence to plant it or cause it to grow in the wild.

The story is worth knowing for one reason. Nothing about giant hogweed's arrival was accidental — it was chosen, bought and planted because it looked impressive. It remains the standing argument for checking a striking unknown plant's regulatory status before putting it in the ground.

A cool, damp-climate plant of roughly zones 3-7: the Northeast, Great Lakes, Pacific Northwest and southern Canada, following streams, ditches and woodland edges. Uncommon in the hot South - but a report matters anywhere.

Giant hogweed is a plant of cool, moist temperate climates, roughly zones 3 to 7. Its established North American range is concentrated in New York, Pennsylvania, New England, Ohio, Michigan and the Pacific Northwest, along with Ontario, Quebec and British Columbia, and there are scattered occurrences elsewhere. It is uncommon in the hot, dry Southwest and in the deep South, where summer heat and drought limit it.

Within that range it follows water and disturbance. Stream and river banks are its main habitat, because the seeds float and colonise downstream; after that come ditches, roadsides, rail margins, vacant lots, and the edges of woodland and old estates, where it often persists from a long-forgotten ornamental planting. It tolerates part shade, which lets it invade the shaded riparian strips that many other invasives cannot reach. Its scale means a mature stand shades out everything beneath it, and when the plants die back in winter they leave bare riverbank soil that erodes.

Two practical points. If you live in its core range, learn it before you clear an overgrown streambank or take on a neglected property — that clearing job is when people get hurt. And if you live outside that range, a report still matters: new populations get found because one person recognised one plant, and federal listing means every state has an interest in an early find.