Giant hogweed, also known as giant cow parsnip, is not usually thought of as an environmental concern. Some see it simply as a beautiful plant with gorgeous blooms.

This perennial plant, however, is considered a noxious weed that has become a thorn in the side of German authorities in recent years. It has grown rapidly and has overrun many areas. It is also considered an invasive plant species in the United States.

“Giant hogweed is a public health hazard that ranks even higher than poison ivy, poison oak, and poison sumac, in respect to its potential to harm humans,” the U.S. Department of Agriculture states on its Web site.

The warning continues: “The sap from this plant can cause a severe skin reaction known as photodermatitis or photosensitivity. The reaction can occur up to 48 hours after contact. After coming into contact with the sap, the skin blisters when exposed to sunlight. Contact with the eyes can lead to temporary or even permanent blindness.”

This plant is detrimental to the health of humans and animals, and is regarded from an ecological perspective as a serious problem. As of 2009, the weed has taken root all over Hamburg, Germany. The Hamburg government is waging a complex war against this transplanted intruder, which is not native to Europe.

Eimsbuettel, a Hamburg suburb, has implemented a new strategy in its fight against giant hogweed. Instead of cutting down the weed before it blooms, such as is practiced in other suburbs and in an area in Hamburg proper, Eimsbuettel has initiated a pilot project. This suburb’s local government has sent out crews to dig up the weed. It will continue to do so over the next seven years, or cover the plant with a weed blocker. Since the seeds of this plant can survive for up to seven years, the blocker has to remain in place for that long.

“Digging up the giant hogweed is without a doubt the most effective tool against this plant. It blocks the plant from further propagation,” commented Helge Masch, head of the Special Botanical Garden of Wandsbek. Cutting the weeds down is not effective, and he is very critical of such an approach, which would require that the plants to be cut down every year for up to four years, and several times during the year, as the plant grows a penury bloom once cut down.

Sabine Meindl, the representative for the giant hogweed action group in Eimsbuettel, explained that local governments contact the owners of gardens in the area where the weed has been spotted. The plant is actively pursued on public domain. However, when found on private property, owners can only be advised to eradicate the weed. They cannot be forced to do so.

“The problem we encounter is that we proactively fight the plant on public property and once we turn around, it stares back at us from private properties. This plant is blooming, sending its seeds onto public grounds the minute the wind picks up. This undermines our efforts of fighting the plant on public domain,” Meindl said.

“The plant should be destroyed on private ground as well, and we have to notify the owners about this matter. But unfortunately, there is no a law that forces the owners to remove the plant in Germany.”

She concluded: “There is a law in Scandinavia, but here in Germany, I can only inform and recommend, in hopes that the owners will cooperate.”

Notes About the Plant

Giant hogweed (Heracleum mantegazzianum) was originally found in Central Asia’s Caucasus region. It was brought to Europe as a botanical curiosity in the 19th century, and to the U.S. in the early 1900s. Unfortunately, it has spread rapidly and widely. It can grow to a height of 15 to 20 feet.

The blooms appear in the form of a white, umbrella-like cluster, usually appearing between July and September. The plant belongs to the Apiaceae family, and is related to the carrot and parsley family. It resembles common hogweed.

In Hamburg, the plant can be found as an ornamental plant in gardens, or growing wild along train tracks or near small brooks or rivers. In the United States it can be found in a many states.

It can take up to seven years to eradicate this plant—being quite prolific, large colonies of plants have grown from one single plant.

This plant is included in the “Federal Noxious Weed List.” It is illegal to transport it across state lines. Those who do so are subject to stiff fines.

Anyone finding the plant in the United States should contact the U.S. Department of Agriculture. In Michigan, please contact the Giant Hogweed Hotline at 800-292-3939 and staff from the Department of Agriculture will assist in eradicating this pest.

Read this article in German

Heide Malhotra contributed to the article.