The first week of May, the gardening bibles intone, is when those cascades of grape-like petals on the hitherto bare, twisted branches of wisteria turn overnight into a chorus of violet-blue flowers. And this year, for once, nature has played by the rules: the wisteria blossom has magically arrived with all the punctuality of Mussolini-era trains. Right now, houses and gardens are clothed in it, and there is something about the spectacle of stone walls, fences, gable ends or even whole (ideally, thatched), cottages cloaked in these exotic, ostentatious, outsized and very indiscreet blooms that pleases the eye, lifts the spirit and draws attention away – briefly – from worries about hung parliaments, double-dip recessions, crises in the eurozone and bitter economic medicine ahead.
Of course, we know, even as we gaze at it, that the wisteria is just a distraction. Neither the most magnificent specimen in full bloom (the one at Fuller's Brewery in Chiswick, west London, is said to be the oldest in the country), nor this climber's allegedly unique ability to send its scent downwards to perfume the streetscape rather than allow it to rise up on the breeze as is the way with lesser plants, is going to pay those bigger tax bills or decide who ends up in No 10, and for how long.
Or is it? Perhaps not literally, but there may, the experts say, be more concrete benefits to the spectacle of clouds of wisteria blossom. "Over the millennia," says Dr David Holmes, a senior psychologist at Manchester Metropolitan University who has done research work with the Royal Horticultural Society, "humankind has learnt to recognise and react to signs that it is coming out of the hardship of winter into spring. One of the most simple is seeing the green breaking through the white of ice and snow, or flowers appearing on bare branches. These visual signals are now hard-wired into our psyches at a profound and instinctive level. So we are preprogrammed to respond positively to the sight of wisteria blossom."
The blooms appear because the weather is warming and the days lengthening, and those factors, in their turn, spark a hormonal change in us all. "The brain's chemistry alters," says Dr Holmes, "notably in banishing what used to be called 'winter blues', but is now more accurately labelled seasonal affective disorder or SAD. A hormone is released called melatonin which wakes us up from what you could see as akin to a period of hibernation and lifts our mood."
But the benefits of spotting an eye-catching wisteria, whether it be on a Notting Hill mansion or a council house in Kirkcaldy, may also improve our mental and physical health, according to a study published last week by a team from Essex University, headed by Professor Jules Pretty, in the American Chemical Society's journal Environmental Science & Technology. "We all feel," says Pretty, an environmental scientist, "that spring is a wonderful time for nature, but what we have been trying to do is measure that feeling accurately and therefore lift it out of the realms of quackery."
His paper, A Dose of Nature, finds, in a sample of some 1,250 people, across a range of age groups, that both mood and self-esteem improve significantly in quantifiable ways from contact with nature, especially if that contact includes "green exercise" – i.e. walking, gardening, cycling and countryside sports. "And self-esteem and mood," he says, "are strong indicators of good mental health, and also, in the long-term, of good physical health."
The study shows, for example, that being in a green environment is better than being in an urban one in terms of a measurable positive effect on blood pressure, hormones and stress levels. Intriguingly, it also concludes that the biggest beneficial boost from exposure to nature is gained within the initial five minutes of each encounter with the great outdoors. While it continues to reap a harvest thereafter, the crop of positives diminishes. So, it will be the first few steps of a walk through a spring garden that changes your mood most, rather than clocking up the first mile.
I decided to put the theory to the test with a trip to Hampstead Heath on election morning. Thankfully, there hadn't been any of the reported queues or confrontations at my local polling station, but election day is always stressful for parents of school-age children because, despite the major parties trumpeting their family-friendly credentials, they don't hesitate to close schools to make way for ballot boxes. What politicians like to call "hard-working families" are thus given the additional challenge of balancing employers' demands with young children that day.
It would be an understatement to say that, by the time I reached the heath, having left at home a truculent teenager determined to do his own thing but rather vague as to what and whom that might involve, I was a bit scratchy. I had in tow two fractious children, plus a dog in season, and a mobile phone ringing non-stop. At least there were parking places, but then I discovered I had no change for the meter, had left the dog lead behind on the kitchen table, and had brought the wrong footwear, this being a morning for dusting down sandals in preference to the Wellingtons and thick socks that had been in residence in the car boot for the winter.
Finally, we set off under a blue sky. The path from the car park was lined by walls of red, purple and white rhododendrons. To one side, in a clearing, there was an ancient beech, its leaves just starting on their annual journey from translucent pink to burnished copper. Elsewhere the foliage had the fresh colour of a kiwi's inside rather than the dirty mushy-pea shade of summer.
Was I imagining it, or did the air taste fresher? Was the children's bickering merging seamlessly with the birdsong? And did the dog's overreaching herself to sniff a doberman's backside suddenly seem like just another part of nature's rich tapestry? Perhaps. Certainly the perma-frown on my brow was relaxing and the demands for a vanilla cone at ten o'clock no longer seemed so outrageous. What I needed to reach a conclusive verdict was a fix of wisteria, but half-an-hour's intensive search failed to produce a result, so reluctantly I abandoned the experiment in favour of the ice cream parlour.
According to Pretty, the scientific evidence is a bit thin to prove health benefits are maximised by getting up close and personal with wisteria in the crucial first five minutes of an encounter with nature. "I am not in a position to pronounce definitively," he admits, "on whether wisteria or a carpet of bluebells or – my own favourite – the peppery smell of the oil seed rape in the fields round my home in Suffolk are any more or less effective than each other, though our research did show that if there was a splash of blue present amid the green, particularly in the form of water, then you derive extra benefits. So wisteria may count as your portion of blue."
That feels like stretching the evidence, like wisteria stretched along a wire by gardeners keen to maximise their crop. Science, it seems, can tell only part of the story. Religion has long celebrated the link between nature, landscape and the numinous, most obviously in the creation myths of the different faiths which tell of earth being fashioned by a divine hand. So Celtic monks, in the fifth and sixth centuries gravitated towards islands and exposed stretches of coastline, places such as Iona and Lindisfarne, in part because their geography allowed them a panoramic view of God's creation. These were "thin places", where the boundaries between this world and the next were transcended. Today, the environmental movement stresses each generation's obligations to good stewardship of nature for the sake of the planet's future.
However important we think we are, however all-consuming our needs and worries, nature has the power to dwarf them, not least because of the lifespan of trees and plants – the wisteria at Fuller's Brewery, for example, is still thriving after nearly 200 years.
David Holmes has looked at why we are more attracted to some plants over others. Our choices, he found, mirror our characters. So what does a weakness for wisteria reveal? "That we aspire to the exotic, to the lush," he reports. "And that often our aspirations go beyond our realities." In other contexts that could spell disaster but, in a May garden, that heady promise of wisteria is pure balm.