Giant hogweed is a dangerous plant for two reasons. It is highly invasive, and it is so toxic to humans and pets that it is considered a public health hazard. What makes giant hogweed so vicious is its sap. When it gets onto the skin and is exposed to sunlight, it creates painful burning blisters and long-lasting scars. And if the sap gets into the eyes, it can lead to temporary or permanent blindness. Thankfully, giant hogweed in its mature stage is relatively easy to identify due to its tall stems, wide, deeply-lobed green leaves, and large umbrella clusters of white flowers. Giant hogweed is native to Asia and was introduced to the United States as an ornamental garden specimen in the early 20th century, from which it quickly escaped into the wild.
|Common Name||Giant hogweed, giant cow parsnip, cartwheel flower|
|Botanical Name||Heracleum mantegazzianum|
|Plant Type||Biennial, perennial, herbaceous|
|Mature size||15-20 ft. tall, 5 ft. wide|
|Hardiness Zones||3-8 (USDA)|
|Toxicity||Toxic to humans, toxic to pets|
Giant Hogweed Invasiveness
Under the Plant Protection Act, giant hogweed is classified as a federal noxious weed that is prohibited from entering the United States, and being transported across state borders.
A single giant hogweed produces up to 20,000 seeds. When not controlled, it spreads quickly, creating dense monocultures that choke out native and desirable plants, especially along waterways. This, in turn, can adversely affect the environment as the plant can contribute to erosion and outcompete plants that local wildlife needs to thrive. After the plant flowers and sets seed, the plant and the root die but that’s not the end of it. If the root has developed side shoots, new plants may emerge from it.
What Does Giant Hogweed Look Like?
True to its name, giant hogweed is a giant in every respect. The mature plant is easy to identify. It grows up to 15 to 20 feet tall, its compound leaves can reach a width of up to five feet, and the flower clusters can have a diameter of up to two and a half feet. The stems and leaf stalks are sturdy, dark-reddish spotted, and hollow, between two and four inches in diameter. The wide, flat-topped flower clusters consist of many small white flowers. Flowers appear in June or July, and seeds set it August.
Ideally you should identify a giant hogweed long before its towering and mature. The growing cycle can give you cues for its identification. As a biennial or perennial, the vegetative parts, basal-leaf rosettes, die back in the winter. The plant starts regrowing in the early spring. It can take a giant hogweed three to four years until flowering.
How to Get Rid of Giant Hogweed
When removing a giant hogweed, always wear protective clothing and cloves. Make sure that there is no gap between your sleeves and gloves that could exposes bare skin when you move your arms.
Small plants can be manually pulled. Larger plants need to be dug up. If the plant is already large, make sure to remove it before it produces any seed. Digging up a mature giant hogweed is work, because it has a taproot up to two feet long, and you need to make sure to remove the entire root system.
If the plant is mature, you must also protect your face, so it does not get exposed to any of the plant parts when you take it down.
For plants that are too large to discard in the household trash, at a minimum dispose of the flower heads in order to prevent the seeds from spreading. Move the remainder of the plant to the compost, or to a location out of the reach of humans and pets where it can decompose.
Mowing giant hogweed is not an option, because above-ground plant parts that are cut before the plant flowers and sets seeds may regrow.
What is the difference between giant hogweed and poison hemlock?
Poison hemlock has fern-like foliage, unlike giant hogweed. Another difference is the stem of the giant hogweed, which has purple blotches and white hairs. Poison hemlock has a smooth stem with purple blotches but no hairs.
Where is giant hogweed native?
Giant hogweed is native to the Caucasus Mountains between the Black and Caspian Seas in Georgia, Azerbaijan, and southern Russia. It was introduced to the United States as an ornamental garden plant in the early 20th century.
Where is giant hogweed found?
Giant hogweed grows in different habitats. It is frequently found along roadsides, ditches, vacant lots, wooded or open spaces between residential areas, and along stream banks and rivers.