Giant Hogweed

Heracleum mantegazzianum

Plant Description

Large, tall plant with large leaves and flower head. Flowering salk develops after 2-4 years. Stalks are hollow with purple blotches and sparse hairs. The flower head is a large umbrella-like cluster up to 2.5 feet in diameter. Leaves can be 3-5 feet wide and deeply lobed with pointed ends. PLANT SAP IS EXTREMELY TOXIC.

Plant Details

Life Forms	Forb
Habitats	Disturbed sites
ODA Listing	A
Soil and Moisture Conditions	Moist
Suggested Actions	Report to Oregon Invasives Hotline
Shade Preference	Full sun Part shade
Mature Height	10-15'
Distribution	Washington, Oregon Alaska
Control	The plant is highly toxic and should only be controlled by a professional. Wear gloves and protective clothing, small plants can be pulled; herbicide is effective.
Disposal Methods	Bag all flower heads in sturdy garbage bags. If the plants are in seed, carefully cut off the seed head and place in a bag without dispersing the seeds. Dispose of flower heads and plants in household garbage or take to a transfer station for disposal. Do not compost or put in yard waste. Never dump plant material because weeds can spread from yard waste piles
Reproduction and Spread	Mid-May to July, produces 2-foot-wide umbrella-shaped clusters of small white flowers that go to seed in July. Reproduces by seed.
Introduced	1917 from Caucus Mountains
Look Alikes	Cow parsnip resembles giant hogweed but is much smaller, lacks the red spots on the stems, and is far less dangerous. Giant hogweed stalks are mottled red like its close relative poison hemlock. Cow parsnip stems are solid green
Impact	Spreading by seed, giant hogweed has escaped into numerous backyards, ravines, parks, abandoned lots, Streams, woods, and roadsides. It can crowd out other plants and take over natural areas, especially in moist areas such as Streamsides. Somewhat shade tolerant, giant hogweed can also thrive in full sun and has been known to even invade healthy turf. A public health hazard, hogweed's clear, watery sap has toxins that cause photo-dermatitis. Skin contact followed by exposure to sunlight produces painful, burning blisters that may develop into purplish or blackened scars
More Info	https://kingcounty.gov/services/environment/animals-and-plants/noxious-weeds/weed-identification/giant-hogweed.aspx