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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Friday 24th June 2011

To Edinburgh, as the proper diarists used to say, for my wife’s third dental appointment in a course of six that might see her with top teeth after an absence of eighteen months. In 2010, Edinburgh was ‘Heracleum heaven’ as everywhere you looked, it seemed, there was giant hogweed flourishing.

Heracleum mantegazzianum, giant hogweed

And not just on the banks of watercourses where we tend to think Heracleum mantegazzianum likes to make its home. Every piece of derelict land, every quiet corner of a park, every untended end of a large garden seemed to be proudly displaying its large white flowers or, later, its huge seed heads carrying enough potential plants to ensure many years of ‘hogweed hell’.

There is a certain irony to finding Heracleum mantegazzianum growing in those large gardens. I suspect that many of them are Victorian mansions, previously home to some prosperous merchant with his family, servants and gardeners. With society’s changes, the prosperous merchants now live in the modern 4-bedroomed detached house close to the golf club on the fringes of the city or in a plush apartment overlooking the docks at Leith. Either way they live without their servants apart from the occasional au pair or the ‘lady who does’ coming in a few days a week.

That left many large, solidly built mansions with no apparent purpose in life until the arrival of the independent single, the weekdays only city dweller, the foreign student and the new couple. These new types of household created the demand for smaller accommodation with few, if any, responsibilities to the property itself or its surrounding land and the era of the MDU (multiple dwelling unit not to be confused with the much older tenement slum) had arrived.

In some cases, as well as the mansion itself being converted into numerous studio, one-bed or two-bed flats, planning permission was obtained to enable a new block to be built in the former grand garden and the problem of tending such an area was removed. In many places, however, the gardens remain and their care is in the hands of a management company under pressure from the residents to keep its charges low and under pressure from its owners to make as much profit as possible from those charges.

It’s little wonder that such garden maintenance as there is concentrates on providing a bit of clear land adjacent to the property for a communal barbecue ‘venue’ with areas under, and beyond, the mature trees further from the house left to run wild. No doubt, in many cases the residents are proud of this neglect because they’ve bought into the message of encouraging wild gardens for the benefit of birds and insects and biodiversity in general.

But, in these areas, the plants can get on with it themselves and the most vigorous will prosper. Heracleum mantegazzianum is certainly up there in the top five, though it can’t claim the number one spot. And so, when you drive around the inner suburbs of Edinburgh you see plenty of giant hogweed popping its head over the top of the old stone wall built to stop intruders from getting in but unable to stop seeds of invasive plants getting in and, then, passing on seeds further along the road.

Heracleum mantegazzianum, giant hogweed

The irony in this is that Heracleum mantegazzianum is back home in many cases. The plant was first brought to the UK in Victorian times by plant hunters who saw a good profit in persuading the wealthy that having it in one’s own garden would make a statement about one’s wealth and stature as well as providing a stunningly beautiful flower. Because, the giant hogweed does have a beautiful flower but, knowing its harmful abilities, we tend to ignore that these days.

I’ve written before about how it is that we took to Heracleum mantegazzianum without worrying about its ability to cause severe and long-lasting harm. On balance, I think it didn’t display these tendencies to any extent in its native area but, I suspect, some would argue that the rapacious plant traders didn’t care about the harm they could be spreading as long as they made a good profit.

Anyway, back to today’s trip to Edinburgh. Stopped at the traffic lights at Lothianbridge, I noticed a sprayed giant hogweed in the roadside verge a sign that the local highways authority is doing what it can. Then, just after passing Dobbies Garden Centre, a substantial patch comprising a dozen or so plants had been sprayed and was dying off. Along the River Tweed, spraying tends to be done as soon as the plants begin to appear in a systematic programme designed to achieve eradication in the long-term. Given that the plants by Dobbies were a couple of metres tall and in flower, I suspect that the spraying was reactive following a complaint from the public.

A reactive approach, if that is what it was, will never be completely successful but, as pointed out on TV this week, eradication programmes may never be the answer. The plant being discussed was Fallopia japonica, Japanese knotweed, the plant that keeps giant hogweed off the top spot in the 'invasive incomers' chart, and the programme was ‘The Wonder of Weeds’ presented by Chris Collins.

I suppose I’m displaying my prejudice when I say I’m not sure whether Chris Collins gets TV work because he is one of the best gardeners in the country or because of his Cockney accent but I was surprised that a programme about weeds wasn’t being presented by Richard Mabey whose book ‘Weeds’ almost certainly gave the TV commissioning editor the idea. Mabey did appear, briefly, but I’d rather have seen more of him and done without the, apparently obligatory these days, section on ‘natural remedies’ made from weeds.

On Fallopia japonica, the programme showed stop-motion footage of knotweed bursting through concrete paths and showed efforts to eradicate it both professionally and by volunteers. I was amused when the professional described in detail the precautions necessary for disposing of the removed plant including burning it on site in cages to stop the smoke carrying away any viable plant fragments. Behind him, his employees were happily piling up the plant on top of the cage so that the rising flames from the material lower down could have a good chance of spreading it further.

That scene seemed to confirm that eradication is not a matter of having enough money to fund the projects as is often stated. It’s simply that we haven’t found the best way to deal with the situation. ‘The Wonder of Weeds’ did make this point and went on to talk to a scientist who, after ten years of work, has been able to both find an insect that, in Japan, keeps the native knotweed in check and has, finally, received permission for this insect to be introduced in trial areas of the UK.

Some years ago, I read that scientists had found a fungus that seemed to control Heracleum mantegazzianum in its native lands but I haven’t heard any more since. I don’t know if the work is continuing or has come to nothing. Or whether the piece I read about ‘fungus’ and ‘giant hogweed’ should have been about ‘insect’ and ‘Japanese knotweed’. After all, the only thing which spreads faster than these invasive plants is misinformation.


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