How To Identify Giant Hogweed

Touching Giant Hogweed can have some nasty effects. Even brief contact with the sap from this plant can scar, burn, or even blind you. The invasive, federally listed noxious weed with a nefarious reputation has origins in the Caucasus mountains and southwest Asia. The plant moved west by way of naturalists in the 1900s who used them in ornamental gardens because of their enormous size and canopy of flowers.

Then, it spread.

The average Giant Hogweed produces an astonishing 20,000 seeds that can drop 30-feet from the plant and move even further when aided by wind or water. The first-ever confirmed Giant Hogweed plants were recently discovered in Virginia. The state now joins several other areas in the  U.S. with reported sightings.

Contact with Giant Hogweed might sound scary, but don’t panic yet. Without question, the best way to prevent injury is by learning to recognize it when you see it and avoid any contact with your skin. Luckily, Giant Hogweeds are big, distinctive plants that are easily identified.

Let’s take a closer look.

How to Identify Giant Hogweed

According to the New York State Department of Environmental Conservation (DEC), giant hogweed is most easily recognized when the plant is mature and filled with flower clusters. However, since these giant plants may not flower for several years — three or four — it’s important also to know how to identify younger plants.

Sosnowsky hogweed (Heracleum sosnowskyi) leaves

Young non-flowering giant hogweed.

Young giant hogweed plants have sizeable basal leaf rosettes with some stems and leaves. In the first few years, the leaves and stems of a young, non-flowering plant will start growing in early spring and die back over winter.

Dangerous toxic plant Giant Hogweed in the field, blooming. Also known as Heracleum or Cow Parsnip

Giant hogweed about to bloom. 

Mature giant hogweed plants will begin to flower in June – July and go to seed in August. Interestingly, after the mature plant flowers and goes to seed, the whole plant including the root dies. An exception to this rule is if flowering plants are damaged or cut above the root before the flowers open. In these cases, the plant may survive a few more years.

Lush Wild Giant Hogweed plant

Mature wild giant hogweed in bloom.

Even though they tend to die after flowering, giant hogweeds are actually perennial in nature. The plants have long branching taproots that can grow up to 24 inches (60cm) long allowing for the development of side shoots which can sprout new plants the following year.

Giant Hogweed  or Heracleum

The purple-splotched stem can help identify giant hogweed.

When attempting to identify a giant hogweed plant, look for these four characteristics:

  1. Mature plants have large white flowers with 50-150 clustered into an umbrella shape that can be up to two feet across with five-foot-wide lobed, jagged leaves.
  2. Plants are between seven and 14-feet tall, depending on factors such as age, growth, and whether or not the plant has been mowed or cut.
  3. The ridged stems are green with extensive purple splotches and prominent white hairs. Look for stems that are 2 – 4 inches in diameter with a thick circle of hair at the base of the stalk.
  4. After flowering, the plant will go to seed. Seeds are dry, flat, oval, and tan with brown lines.

Look for giant hogweed in places with open sites with tons of sunlight, moist soil, particularly along waterways like rivers and streams, roads as well as in fields, forests, or backyards.

What To Do If You Find Giant Hogweed

Because Giant Hogweed can be invasive and harmful to humans, there are certain precautions to take if you suspect you’ve found some growing.

First things first, obviously don’t touch it the plant.

Report your discovery to a local authority like your county noxious weed coordinator and report your sighting online. Even if you’re unsure, it’s always better to report a sighting. It’s helpful to include photos and the GPS location of any plant you find. Local authorities will advise you on the next steps, which could include them removing the plant or advising you on how to do it yourself safely.

Do not attempt to remove Giant Hogweed without protective gear or without the appropriate advice from a professional.

What To Do If You Touched Giant Hogweed

Merely brushing up against a Giant Hogweed with exposed skin can cause a severe reaction called phytophotodermatitis. In basic terms, the sap prevents your skin from being able to protect itself from the sun. Without this protection, your skin ends up with very severe burns.

Skin exposure leads to extreme skin blistering when exposed to sunlight, eye contact can lead to temporary or permanent blindness, and if inhaled it can cause severe respiratory issues. Not only that but sweat or dew can worsen the skin reaction and the sensitivity to sunlight can last for years.

Since the phototoxic reaction can begin as quickly as 15 minutes after contact, if you come into contact with the sap:

  • Move out of the sun and immediately wash the affected area with soap and cold water.
  • Cover the exposed area. If the area is blistered, covering it with long-sleeves won’t be enough. Wrap the area with a bandage or wear UV-protective clothing. (You’ll have to protect these areas from sunlight for the next few years as well.)
  • If the eyes are affected, rinse them with cool water and wear sunglasses.

Make sure to contact your doctor ASAP for further treatment.

Have you ever encountered Giant Hogweed before? Share your stories in the comments.

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Photos: Thinkstock