Heracleum mantegazzianum (giant hogweed)

Skye Pelliccia, no rights reserved (CC0) · iNaturalist

1 / 4

Heracleum spp.

hogweeds

Apiaceae

Temperate Northern Hemisphere - North America, Europe, and Asia, including the Caucasus and central Asia

Attracts Pollinators Attracts Butterflies

Native to North America

SunFull Sun – Part Shade

WaterMedium

HardinessZones 3–8

Overview

Heracleum spp. is a genus of roughly 60 to 100 biennial and perennial herbs in the carrot family (Apiaceae), known as hogweeds and cow parsnips. Plants form a basal rosette in the first year and send up a hollow, ridged, often bristly flowering stem in later years, reaching 3-18 ft (0.9-5.5 m) tall depending on species. Leaves are large and compound, pinnately divided into broad toothed or lobed segments, with the biggest leaves of H. mantegazzianum spanning 3-5 ft (0.9-1.5 m). Tiny white to greenish-white flowers crowd into broad flat-topped compound umbels 4-32 in (10-80 cm) across, the outer flowers often enlarged. Flat winged seeds follow and scatter near the parent. Sap of several species, above all giant hogweed H. mantegazzianum, contains furanocoumarins that cause phytophotodermatitis, producing burns and blisters on skin exposed to sunlight after contact. The genus is native across the temperate Northern Hemisphere. Some species are regulated as noxious or invasive, while native cow parsnip H. maximum is a normal part of North American meadows and streamsides.

Native Range

Heracleum spp. is native across the temperate Northern Hemisphere, with species in North America such as H. maximum, in Europe and western Asia such as H. sphondylium, and in the Caucasus and central Asia, where H. mantegazzianum originates. Plants grow in moist meadows, woodland edges, streambanks, and roadside ground. Several species, including giant hogweed, are regulated as noxious weeds in parts of North America and Europe.

Suggested Uses

Native species such as cow parsnip H. maximum are planted in moist meadows, rain gardens, naturalized streambanks, and pollinator plantings. The broad umbels feed a wide range of insects. Giant hogweed has no garden use and is targeted for removal where it occurs.

How to Identify

Recognize Heracleum spp. by its tall hollow stems, very large pinnately divided leaves, and broad flat compound umbels of small white flowers. Giant hogweed H. mantegazzianum stands 8-18 ft (2.4-5.5 m) tall with purple-blotched, bristly stems 2-4 in (5-10 cm) thick, while native cow parsnip H. maximum is shorter at 3-8 ft (0.9-2.4 m) with green stems. The clear watery sap causes skin burns when exposed to sunlight, a trait that separates Heracleum spp. from harmless look-alikes such as wild carrot.

Appearance

Size & Dimensions

Height3' - 18'

Width/Spread2' - 6'

Colors

Flower Colors

white

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~6 weeks

Spring Summer

Heracleum spp. flowers in late spring through summer, generally June to August, in the year the plant bolts. The large white umbels open over several weeks and draw many flies, beetles, and bees. After flowering, biennial and monocarpic species set seed and die, while perennial species return from the rootstock.

Detailed Descriptions

Flower Description

White to greenish-white

Foliage Description

Green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-8 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5(Neutral)

357912

Soil Types

loam clay silt

Drainagemoist

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

2-5 years to flowering

Care & Maintenance

Care Guide

Heracleum spp. grows in full sun to part shade in moist, fertile soil and tolerates a soil pH from about 5.5 to 7.5. Native species such as H. maximum suit moist meadow and streamside plantings and are hardy across USDA zones 3-8. The plants self-seed readily, and giant hogweed in particular spreads into disturbed ground where it is regulated as a noxious weed. Contact with the sap followed by sun exposure causes painful skin burns and blisters, so the genus is grown with caution and giant hogweed not at all in most regions. Few diseases affect the plants, though aphids and leaf miners use the foliage.

Pruning

Flower umbels are cut off before seed sets to limit self-seeding, a common step with the weedier species. Old stems and foliage are cleared after they die back in autumn. Removal of giant hogweed is regulated and is carried out by trained crews using protective equipment because of the burning sap.