The giant hogweed (Heracleum mantegazzianum), also known as Hercules perennial or Hercules herb, is one of the so-called neophytes. This means that it has settled in different regions without human intervention and is spreading. The problem with this perennial is that it is poisonous and spreads rapidly. Even simple skin contact is enough to cause painful skin reactions in humans and animals. In this guide, we clarify whether there is an obligation to report when you discover giant hogweed and what you should pay particular attention to when handling the plant.

recognize giant hogweed

Giant Hogweed (Heracleum mantegazzianum) is actually a beautiful plant with a majestic shape, which can quickly hide the danger it poses. Therefore, these poisonous plants should be combated promptly and effectively. It’s easier the earlier you start.

  • Designation ‘Bärenklau’ in the name is misleading
  • Heracleum mantegazzianum does not belong to the Bear Claw species
  • It is a Mediterranean wild perennial
  • Initially recognizable by a rosette
  • With up to one meter large, strongly pinnate leaves
  • Can reach heights of growth of 150 to 300 cm within a few weeks
  • Sometimes up to 400 cm possible
  • Stems are up to 10 cm thick, hollow and hairy with red spots
  • Flowers white to pale pink and plate-shaped
  • Consists of many small individual flowers
  • Flowering time is from June to July
  • Flower umbels reach diameters between 30 and 50 cm
  • Leaves are green and between 100 and 300 cm long
  • They are three, five or nine parts

A single plant can form an average of around 20,000 seeds per year, through which it can spread rapidly. However, it is not quite so easy to recognize the Hercules perennial, because there are other plants that sometimes look confusingly similar to it. Some of them are completely harmless, others even surpass them in their toxicity.

Risk of confusion – information

The harmless doppelgangers include the angelica, a traditional medicinal plant, the hogweed, cow parsley, wild carrot, wild fennel, the greater burnet, a popular herb for salads, as well as sweet umbel and goutweed. On the other hand, the danger of the spotted hemlock should not be underestimated, which can be recognized above all by its intense smell of mouse urine and which can reach heights of growth of up to 200 cm. Dog parsley (Aethusa cynapium) is on a par with hemlock in terms of toxicity. Both plants contain the neurotoxin coniin in all parts of the plant. The concentration is highest in the seeds.

No obligation to report giant hogweed

Even if some plants in the garden are poisonous for both humans and animals, they are not subject to reporting in Germany, nor is the giant hogweed. In contrast to public places, where the Federal Nature Conservation Act applies and the giant hogweed is prevented from spreading, it is very different in the home garden.

If the plant spreads here, it is at your own discretion or the responsibility of the garden owner how this plant is handled. Even if there is no obligation to report these, like many other poisonous plants, that does not mean that giant hogweed is harmless. On the contrary, due to their potential danger, it is definitely advisable to fight them early and intensively.

What makes this plant so dangerous

  • Highly toxic effect is based on so-called furanocuramines
  • Furanocuramines are phototoxins
  • Are also contained in small young plants
  • Only develop their toxic effect under the influence of sunlight
  • When exposed to UV light, the body’s own proteins react with these toxic substances
  • This can lead to severe skin reactions
  • Symptoms not immediately recognizable or noticeable
  • Usually only appear days later
  • Simple skin contact with this plant is already sufficient
  • Reddening of the skin and itching, up to the formation of blisters possible
  • Blistering similar to symptoms of a first or second degree burn
  • The resulting weeping wounds heal very poorly
  • Often only after several weeks

Other signs of poisoning can be fever, sweating and even circulatory shock. Particularly sensitive people do not even have to come into skin contact, just being in the vicinity of this plant can lead to respiratory problems. The giant hogweed is not only poisonous to humans, but also to dogs and cats.

First aid info

If you have come into contact with the plant, affected skin areas must be protected from sunlight immediately and rinsed thoroughly under running water and with soap. They are then cooled with a towel soaked in tap water and sunscreen is applied to prevent blisters and burns. Appropriate protection is particularly important in the first two hours after contact, because this is when the poison reacts most intensively with sunlight.

You should also apply sunscreen regularly in the coming weeks and months. However, if skin reactions occur, such as severe redness, burn blisters or allergic reactions such as shortness of breath, you should consult a doctor as soon as possible. This also applies to pets that have had contact with the giant hogweed, they should definitely be brought to a veterinarian.

Do not fight without adequate protective measures

You should start combating Heracleum mantegazzianum as early as possible. Self-protection has the highest priority. The whole body should be protected, preferably with overalls, goggles, respiratory protection, gloves and boots. Every inch of skin must be protected from the plant’s poison. If they are already relatively high, it is advisable to use pruning saws or pruning shears with a telescopic handle. In this way you can protect yourself from the toxins of the plant caused by falling clippings.

Tip: Anyone who is unsure whether it is actually giant hogweed (Heracleum mantegazzianum), or has questions about reporting requirements or how to combat it, can contact the local nature conservation authority.

Information on correct combat

The best time to combat this poisonous plant in the garden is in March and April, in any case before flowering. At this time the plants have not yet reached their final size and are therefore easier to manage. It is best to choose a day with an overcast sky, no sunshine and only light winds. A rainy, windless day would be ideal.

  • In the first step, cut the plant close to the ground before the central umbel opens
  • The stems together with the umbels of flowers
  • Cutting off the entire plant alone is not sufficient
  • Effect only short-term and not sustainable or permanent
  • Plant keeps sprouting and spreading
  • Forms reserves for renewed flowering before the fruit ripens
  • Sustainable combat only possible by digging out
  • Hercules perennial has a turnip-like root
  • So-called vegetation cones must be excavated from this
  • Use a sharp spade or pickaxe to do this
  • Prick about 15-20 cm into the ground and cut off the relevant part of the root
  • The part underneath rots in the ground
  • Follow-up inspection initially until October
  • Formation of new offspring possible at any time
  • Should be removed as soon as possible

Annual follow-up checks in the spring are also indispensable in order to effectively combat this harmful plant and to nip a reappearance in the bud. It is also possible to cover the floor with black foil, eg pond foil, to prevent the light from entering. On the one hand, this is intended to prevent the seeds from getting light to germinate and, on the other hand, to support the rotting of the remaining root remains. The film must then remain on the ground for a few months. If you take this information into account and stay on the ball, Heracleum mantegazzianum can be permanently eliminated, at least in your own garden.

Tip: The vegetation cone is the tip of the shoot where the length growth takes place.

Do not put clippings on the compost

It is best to incinerate the clippings or dispose of them with the residual waste. The domestic compost heap, on the other hand, is not suitable, because temperatures of at least 70 degrees are required to compost the plant remains and seeds. A self-made compost heap usually has temperatures of a maximum of 40-45 degrees inside. They are far from enough to completely kill seeds and root residues as well as other germs.

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