Giant Hogweed

Giant Hogweed (Heracleum mantegazzianum) is one of the largest herbaceous plants in this country. It is generally regarded as a short lived perennial, typically taking between 3-5 years to reach maturity, flower, set seeds and die. However in less than optimum conditions or as a result of disturbance it may take up to 12 years to set seeds and die. In its early years, it may be lost amongst other vegetation and can easily be overlooked. However in its final year, it grows up to 5.4m in height before flowering. A single plant may set between 20,000 and 50,000 seeds.

Giant Hogweed invading a house!

Giant Hogweed is (or should be) a serious concern for landowners, as the sap is photosensitizing on human and animal skin. Severe and painful burns to the skin are common following exposure and full recovery from these effects can take months or even years; scarring of the skin may also result. More severe results from exposure to the sap are not unknown, blindness (permanent or temporary) has been reported, as has death.

Giant Hogweed in early spring.

If anyone has been exposed to the sap, recommended first aid includes:

  • Keep any areas of skin exposed to the sap away from sunlight
  • Wash skin with soapy water
  • Irrigate eyes (if sap has come into contact with eyes) with eyewash solution
  • Seek medical advice – NHS Direct will be able to advise you further

Treatment of Giant Hogweed is a fairly simple matter in that it is susceptible to several professional herbicides and the growing plants can be killed quite successfully, following 1-2 treatments. However it does require a specialist risk assessment and protective clothing is required. Such clothing may need specialist disposal if contaminated with Giant Hogweed sap.

While the growing plants may readily be killed, the dormant seeds may take up to 5 years to grow, so annual visits to kill new seedlings will be required for at least this period.

Other treatments are available for construction sites, but all treatments require an initial herbicide treatment and at least 3-4 weeks to allow the plant to die, before works can start safely.

All methods must be individually priced. Control measures for smaller infestations of knotweed may be discussed on the telephone but site visits are normally arranged and more detailed quotations offered.

Site visits are normally not charged but, due to the expertise of this company, full technical reporting in some instances, may require an agreed charge with the client before that visit.

Contact Brian Taylor on 01327 340770 or email me on

Operator spraying Giant Hogweed with a long lance.