Sandy’s Garden ... Giant Hogweed – a burning issue

Sandy Simpson
Sandy Simpson
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The well-named giant hogweed has featured prominently in the media in recent months.

It is almost always because people have suffered what are often described as ‘burn-like’ injuries after having come into contact with the plant, either intentionally by trying to pull it out of the ground or by deliberately snapping a stem, or unintentionally by simply brushing against it. The plants were introduced into Britain during the earlier years of the nineteenth century, the first recorded instance being in 1817 when the Royal Botanic Gardens in Kew on the then-outskirts of London offered giant hogweed seeds in their Plant List. These seeds were imported from the Gorenki Botanical Gardens near Moscow, vast botanical gardens which were developed by the prominent family line of the Razumovsky counts in their private estate. These gardens flourished for rather less than twenty years, but left a legacy which continues to this day in the shape of the giant hogweeds whose seed they supplied to other botanical gardens throughout Europe. The seeds were soon featured in seedsmen’s catalogues and the tall, impressive plants were widely planted in ornamental gardens throughout Britain.

Finding the British climate to their liking and lacking any natural enemies … pests or diseases … in their new environment, the seed of these initially-cultivated plants lost no time in escaping into the wild. They were noted in Cambridgeshire in 1828, although it is very likely that this is merely the earliest recorded instance of giant hogweed growing wild in the England and that the first wind-blown seed had spread into the countryside earlier than this. Giant hogweeds … and yes, there is more than one species, the most common being Heracleum mantegazzianum, the species named in honour of Paolo Mantegazzi, the Italian neurologist, (mantegazzium) of the plant named after Hercules (Heracleum) … are not fussy about where they grow and have spread to woodland, heathland and common land throughout the British Isles. Happiest to settle initially in uncultivated land in a new-to-them area, they are very willing to spread to nearby cultivated land. Wherever they become established, the giant hogweeds out-compete desired plants and, in consequence, are officially termed ‘invasive aliens’. Farmers and gardeners can deal with them by uprooting the plants or by smothering them with a mulch, preferably, of course, when they are still young and small. Where such control is not possible, there are effective, if expensive, chemical weedkillers. But none of these methods can be used to deal with giant hogweed infestations in the countryside, where the plants pose a severe threat to wild or other uncultivated environments.

The Royal Horticultural Society offers this advice: “When controlling giant hogweed always wear gloves, cover your arms and legs, and ideally wear a face mask when working on or near it. Cut plant debris, contaminated clothing and tools are potentially hazardous too. Wash any skin that comes in contact with the plant immediately. Ensure that contractors working on your land are aware of the risks and competent to deal with this weed.” And for a scientific explanation of the need to take these precautions, I turned to the website of the New York State Department of Environmental Conservation. There, I read: “When giant hogweed sap, which contains photosensitizing furanocoumarins, contacts human skin in conjunction with sunlight, it can cause phytophotodermatitis - a serious skin inflammation. In brief, the sap prevents the skin from protecting itself from sunlight, which leads to a very bad sunburn. Heat and moisture (sweat or dew) can worsen the skin reaction. The phototoxic reaction can begin as soon as 15 minutes after contact, with sensitivity peak between 30 minutes and two hours after contact.” And there you have it; giant hogweed doesn’t cause ‘burn-like’ injuries. The plants’ sap lets the sunlight cause very real and sometimes very serious burns.

Nasty!