Heracleum mantegazzianum
WARNING: LOCALLY INVASIVE SPECIES
Common Name: giant hogweed
Type: Herbaceous perennial
Family: Apiaceae
Native Range: Western Caucasus
Zone: 3 to 9
Height: 8.00 to 15.00 feet
Spread: 3.00 to 4.00 feet
Bloom Time: June to July
Bloom Description: White
Sun: Full sun to part shade
Water: Medium
Maintenance: Medium
Suggested Use: Naturalize
Flower: Showy
Attracts: Butterflies
Giant hogweed is on the Federal Noxious Weed list which prohibits the importation, interstate transportation and sale of this plant without a permit.

Culture

Giant hogweed is on the Federal Noxious Weed list which prohibits the importation, interstate transportation and sale of this plant without a permit. The two main vices of hogweed are (1) it is an invasive self-seeder that colonizes and crowds out native species plants and (2) it produces a sap which, on contact with skin, leads to a skin reaction known as phytophotodermatitis in which severe blisters and rashes typically occur when the skin is exposed to ultra violet light (sun or UV rays). Giant hogweed easily grows in moist, fertile, well-drained soils in full sun to part shade. Best performance is in full sun. Plants are biennials or short-term perennials. Plants can rapidly colonize areas through self-seeding (wind and water). To help prevent self-seeding, remove and destroy the spent inflorescences of existing plants with care (see below) before seed matures.

Noteworthy Characteristics

Heracleum mantegazzianum, commonly called giant hogweed or cartwheel flower, is an herbaceous biennial or short-lived perennial that is noted for producing rapid and prodigious growth often to the detriment of native plants. Native to Eurasia, it was reportedly first brought to the U.S. in 1917 to an ornamental garden in New York. Ornamental plantings became common prior to the point where the characteristics and problems of this plant were clearly understood. Giant hogweed has over time escaped gardens and naturalized (roadside ditches, stream banks, fields, unused farmland, railroad track right-of-ways and along fences) in a number of areas in North America, primarily including the northeastern and northwestern U.S. plus parts of Canada. In the first year, this plant produces a huge mound of coarse, ternate-compound, basal leaves (each to as much as 3' long) with deeply cut leaflets. In the second year, the plant will rise up to as much as 10-16' tall topped by a gigantic, flat-topped, umbrella-like, compound umbel to 2-4' wide. Each umbel contains thousands of tiny white flowers. Flowers bloom in late June. Sometimes a plant does not flower until one or two years later. After flowering and fruiting, the plant dies. Unfortunately each large flower umbel has about 20,000 seeds. Green stems are hollow and distinguished by white hairs and purple blotches. Giant hogweed is in the same genus as the cow parsnip (Heracleum maximum) which is native to North America.

Genus name comes from a variant of the Greek words herakleia or panakes herakleion in honor of Hercules (Gr. Herakles).

Specific epithet honors Italian anthropologist and traveler Paolo Mantegazzi (1831-1910).

Problems

No serious insect or disease problems. Protective clothing, gloves and eye goggles should be used when working with this plant. Removal of plants from the landscape is best done by application of herbicides. Seeds in the soil can germinate as much as 15-20 years later, necessitating post-removal monitoring.

Garden Uses

None.