In short
- INVASIVE AND DANGEROUS SPECIES — banned from cultivation in the EU; control is mandatory.
- The largest of the „invasive hogweeds” — 2–5 m tall (record 6 m); stem up to 10 cm across with purple blotches, umbel 30–80 cm, exceptionally up to 1 m.
- The sap is strongly PHOTOTOXIC — furanocoumarins + UV = grade II–III burns with blisters up to 48 h after contact. Sap in the eye permanently damages the cornea.
- Native to the Caucasus; introduced to Western Europe in the 19th century as an ORNAMENTAL plant for Victorian parks, escaped from gardens.
- In DE/CH/UK the dominant species; in PL Sosnowsky's hogweed (its twin) is more common. Clinically and legally both are treated jointly.
- Full recognition, protection and control procedures: separate [guide about hogweeds](/en/guide/barszcz-sosnowskiego-jak-rozpoznac/).
Botanical data
- Family
- Apiaceae (Apiaceae)
- Height
- 2–5 m
- Width
- 1.5–3 m
- Habit
- Upright
- Growth rate
- Fast
- Position
- Full sun, Partial shade
- Soil
- Humus-rich, Loamy
- pH reaction
- pH 5.5–7.5
- Moisture
- Moist
- Bloom
- June–August
- Hardiness
- USDA 3a–8b
- Propagation
- From seed
Characteristics
The largest and most recognisable of the „invasive hogweeds” — reaches 2–5 metres in height (record specimens from moist valleys of British and German rivers up to 6 m), with a single straight, hollow stem as thick as an adult's arm (5–10 cm across, exceptionally up to 12 cm). The stem is light green with PRONOUNCED dark red or purple blotches and long streaks — the blotches in H. mantegazzianum are usually more intense and larger than in the related H. sosnowskyi. The stem is covered with stiff, rough hairs. Leaves are huge — up to 3 m long (including stalk), deeply palmately-pinnately divided into 3 large, sharply cut segments, dark green and glossy above; they grow in a rosette from the ground on long, fleshy, hairy stalks. The inflorescence is a gigantic, flat compound umbel 30–80 cm across (record up to 1 m), made of 50–150 rays; each ending in a small umbellet with tiny white flowers. One specimen can produce 20,000 seeds; for comparison Sosnowsky's usually 5–8,000. Blooms from June to August in years 2–5 of life and DIES after seed set (hapaxanthic). The whole plant contains FURANOCOUMARINS — psoralen and angelicin derivatives — which on UVA contact trigger a phototoxic skin reaction. Botanically H. mantegazzianum is very closely related to H. sosnowskyi; differences reduce to the number of umbel rays, fruit shape and stem blotch intensity — in practice, for on-trail recognition and post-contact procedure, they are treated as one species.
Growing and care
Watering
INVASIVE PLANT — not cultivated. In the wild grows in moist, fertile habitats: riverbanks, stream valleys, edges of floodplain forests and abandoned pastures; high soil moisture and full sun favour its mass expansion.
0Fertilizing
Giant hogweed is on the EU list of invasive species of Union concern (Regulation EU 1143/2014). The landowner has a CONTROL duty, NOT of cultivation — hence the fertiliser fields are intentionally left blank.
Planting
INVASIVE AND DANGEROUS PLANT — planting is banned in PL and the EU. If giant hogweed has grown spontaneously on your land, go to the „Pruning” section — control methods are there. Full procedures and personal protection in the separate [guide about hogweeds](/en/guide/barszcz-sosnowskiego-jak-rozpoznac/).
Pruning
Dig up the WHOLE plant with the taproot at least 20 cm below ground — the root alone has reserves to regrow. Protective clothing: impermeable overall, goggles, rubber gloves, mask, rubber boots. ONLY overcast day or after dusk — sunlight activates the sap's phototoxicity. Umbels with seeds collect into sealed plastic bags and dispose of as hazardous waste (not to compost, not to the brown bio bin). In Germany report to the municipal Umweltamt, in Switzerland to the cantonal Fachstelle Neobiota — many councils collect bags for free and fund a professional contractor.
Companion plants
Bad companions
An adult giant hogweed casts deep shade over a several-metre circle and releases into the soil compounds inhibiting the germination of native flora. In the river valleys of Germany and Britain it forms monocultures in which native riparian perennials disappear. There are no „good neighbours” for hogweed — the whole plant must be removed.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Toxicity
| For whom | Level | Notes |
|---|---|---|
| Humans | High | The sap contains furanocoumarins — compounds that on UV contact trigger a strong PHOTOTOXIC reaction. Effect: painful grade II–III burns with blisters, scars and months of skin hypersensitivity. The reaction develops up to 48 h after contact. Sap in the eye can permanently damage the cornea. Immediately after contact: SHIELD THE SKIN FROM SUNLIGHT for 48 h, wash with water and soap, with blisters or facial contact — see a doctor. Full procedure in the [guide](/en/guide/barszcz-sosnowskiego-jak-rozpoznac/). |
| Dogs | High | Furanocoumarins are phototoxic to dogs as well — contact of fur and skin with the sap, followed by sun exposure, causes blisters and burns. Bath with shampoo, avoid sun, veterinary consultation. |
| Cats | High | — |
History and origin
The species was described in 1895 by the Russo-Italian botanists Sommier and Levier in honour of Paolo Mantegazza — an Italian anthropologist and doctor of the second half of the 19th century. Plants from the southern Caucasus reached Western Europe considerably earlier — the first documented introduction to the UK took place in the 1820s, when seeds from Russian scientific expeditions were sent to the Royal Botanic Gardens Kew. The plant made a splash in Victorian parks as an exotic accent — its gigantic scale, white umbrella-like umbel and fast growth suited the aesthetic of the 19th-century „exotic garden” ideally. In the following decades it reached Germany, Switzerland, Scandinavia, the Benelux and North America. First reports of mass burns began to appear as early as the 1870s — however only from the 1960s, when the plant mass-colonised the riverbanks of Germany (Bavaria, Rhineland) and Britain, it was recognised as a problem. Since 2016 it has been on the EU list of invasive species of Union concern (Regulation EU 1143/2014); in Germany, Switzerland, Britain and Scandinavia, control programmes coordinated by local nature conservation authorities have been running for decades.
Uses
Giant hogweed, like the related Sosnowsky's hogweed, has NO admissible horticultural or economic use — it is banned in the EU for planting, transport and sale, and the landowner has a legal duty of control. Historically cultivated in Victorian parks as an exotic ornamental accent (England from the 1820s, Germany and Switzerland from ca. 1890); today treated exclusively as a problem of nature conservation and public health. Contact with the plant serves EXCLUSIVELY its control. The landowner where the hogweed has grown should remove it — best by digging up with the taproot before flowering, in full protective gear, on an overcast day. Full procedures, recognition, personal protection and post-contact procedures for skin or eye — in the separate [guide about hogweeds](/en/guide/barszcz-sosnowskiego-jak-rozpoznac/). Stands of more than a few plants report to the relevant authority: in DE the municipal Umweltamt, in CH the cantonal Fachstelle Neobiota, in UK the local council, in PL RDOŚ — they have programmes and budget for professional control.
Trivia
- The specific name „mantegazzianum” commemorates Paolo Mantegazza (1831–1910) — an Italian anthropologist, doctor and traveller, founder of the Museo Nazionale di Antropologia in Florence, researcher of Caucasian human populations.
- One adult specimen can produce UP TO 20,000 SEEDS — three to four times more than the related Sosnowsky's hogweed; this is one of the causes of the species' aggressiveness along rivers in Germany and Britain.
- In Victorian England, when the plant was introduced into parks, its gigantic scale was considered an aesthetic asset; the first warnings about burns appeared only in the 1870s in British gardening press — and were long not taken seriously.
- Giant hogweed mainly colonises river and stream banks — its seeds are carried by water over great distances, so in Germany and Britain river spates wash new specimens onto previously free grounds every year.
Frequently asked questions
How is giant hogweed different from Sosnowsky's hogweed?
In practice by nothing significant: both are equally huge, have identically phototoxic sap and are subject to identical rules. Botanically H. mantegazzianum is usually somewhat larger (up to 5 m, exceptionally 6), produces more seeds (up to 20,000 vs 5–8,000), has more intense purple stem blotches and an umbel with more rays. In PL H. sosnowskyi is more common (introduced as fodder in the 1950s), in DE/CH/UK — H. mantegazzianum (introduced as an ornamental in the 19th century). For recognition and post-contact procedure they are treated together.
Where in Britain is giant hogweed most common?
Giant hogweed in the UK dominates in Scotland (banks of the Rivers Tay, Clyde, Tyne), in the north of England (rivers Wear, Tees), in Wales (river valleys) and along many watercourses of southern England. It first appeared in the 1820s in London's Kew Gardens and gradually escaped along waterways — its seeds are carried by water over great distances. Local councils in the UK run reporting and control programmes for landowners.
What to do immediately after contact with the sap?
Shield the skin from sunlight FOR AT LEAST 48 HOURS — this is the most important step, because the burn develops only under UV, not from the sap alone. Rinse the spot with plenty of cool water and soap in the shade. Do not rub the eyes. With blisters, contact with face or eyes, in children — see a doctor. Full 5-step protocol in the [hogweed guide](/en/guide/barszcz-sosnowskiego-jak-rozpoznac/).
Can I remove giant hogweed from the garden myself?
Yes, but ONLY in full protective gear (impermeable overall, goggles, rubber gloves, mask), on an overcast day or at dusk. Method: dig up the WHOLE plant with its taproot at least 20 cm below ground before flowering. Mowing is not enough — the plant regrows from the root. Report larger stands to the relevant authority (in DE Umweltamt, in CH Fachstelle Neobiota, in UK local council), which have control programmes and licensed contractors.
Sources
- Plants of the World Online (POWO)Database (GBIF, POWO…)
- Rozporządzenie EU 1143/2014 (gatunki inwazyjne stwarzające zagrożenie dla Unii)Institution / botanical garden
- Bundesamt für Naturschutz — Neobiota-Portal (Riesen-Bärenklau)Institution / botanical garden
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