SCENTS OF CALM
You know spring is here the moment you notice its glorious scent on the breeze. But why does nature create this fragrant symphony? What is it made up of and what effect does it have on our brains? Jane Adams explores the science of wild scents
You can smell spring’s arrival on the air, but why does nature create this fragrant symphony? Jane Adams explores the science of wild scents.
“Blooms burst from leafless twigs, their aroma reminiscent of freshly laundered sheets”
I’m digging over a new vegetable patch. Earth that has been cold for months has been touched by warm sunshine. As I turn the warming soil, it releases a smell so delicious I could happily roll in it. Forget the meteorological start of spring – the season starts right here. It’s the aroma of worms pushing up casts and dragging down decay. It’s green and uplifting, and floods your brain with a feeling of contentment, hinting at the promise of new life.
Humans must have been aware of this earthy, primal smell for millennia – our noses are particularly sensitive to it. The phenomenon is most noticeable when it wafts up from warm, newly turned soil or after spring rain has fallen on dry earth. But it didn’t even have a common name until the 1960s, when two Australian scientists wrote a paper and christened it petrichor: petra (stone) and ichor (ethereal fluid). The source of the smell is a humble molecule named geosmin, which is derived from a single genus of bacteria: Streptomyces, a rich source of antibiotics. For a while, the smell of petrichor is an isolated, albeit welcome, natural scent in the garden. But as weeks pass, the breeze turns sweeter. In the countryside, woodland plants spring into action, making the most of sunlight through the skeletal canopy. With a growth spurt to rival any teenager, their leaves push skywards with flowers and scent soon following. It’s a race. Seeds need to have formed before oak, birch and beech leaves smother the woodland floor with shade.
Out for a walk, the subtle aroma of wild daffodils pulls me to Mountain Clump – a small, wooded hill overlooking our Dorset village. The smell isn’t strong; in fact, its green leafiness with a hint of vanilla comes and goes as I struggle up the hill. But on reaching the top, I realise I’m not alone in the pursuit of scent. Fresh out of hibernation, queen bumblebees crawl drunkenly from flower to flower, intoxicated. In the valley, blackthorn is flowering. From above, this hedgerow shrub looks dusted in snow and meanders chalk-white across the valley floor, following the tarmac of the country lanes. Up close, its blooms burst from black-spiked and leafless twigs, their pure, clean aroma reminiscent of freshly laundered sheets on a wind-whipped washing line.
I contact Amanda Tuke, a Londonbased botanist, to quiz her on her favourite urban spring scent.
“It’s the delicate almond fragrance of winter heliotrope carpeting the banks of my local railway station,” she tells me. I’m surprised. Only the week before, I’d seen this same plant with “handsized circular leaves and bushy pink flowers” on the verge of a lane nearby. Except there was one big difference. To me, it smelt like honey, not almonds.
FRAGRANT FRUSTRATION
Try to describe a smell and, unless you’re a perfumier or sommelier, you are likely to struggle. Some researchers think this phenomenon
is caused by the way our brains process scent and language. Whereas we might find it easy to visually describe a bluebell as being ‘rounded’ and ‘smooth’ with ‘nodding’ flowers, when it comes to its scent, the most imaginative word we might use is, well, ‘bluebell-y’. It could also be that, as English speakers, we just don’t have a need for these words anymore. Elsewhere in the world, the Maniq, a small group of hunter-gatherers in southern Thailand, have up to 15 expressions used to describe smells, but they rely on scent for their survival.
Not only do we stumble over words, but we also differ in how we physically experience aromas. Whereas Amanda’s ‘almond’ may be my ‘honey’, the receptors high up in our nose sometimes struggle to pick up certain smells, or we might hate some odours that others love. Male or female, young or old, all things are not equal when it comes to our fickle sense of smell.
I love dandelions. Their scent reminds me of being a nature-mad six-year-old, stuffing my pockets with feathers, yellow dandelions and pine cones. It feels strange to remember something so clearly from 50 years ago, but smell has a more direct connection to the part of our brain dealing with memory than any of our other main senses. A smell really can transport us back to another time and place.
Of course, these floral scents are not meant for human noses; it’s a happy coincidence that we find them so alluring. Their chief purpose is to attract pollinators, such as bees, moths and beetles. Exuding chemical aromas from their petals, plants are able to attract just the right insects; they rely on their six-legged allies to transfer pollen. Fragrance is their trump card when it comes to reproduction.
For us, it’s more of a mood thing. For years it was thought humans could only detect around 10,000 aromas; it’s now thought this number could be nearer to one trillion. No wonder, then, that we crave fragrant smells after the long, cold, smell-deficient days of winter. As we bury our nose into spring flowers and the minute aroma compounds are picked up by the smell receptors high in the lining of our nose, we seem to instinctively know the brain’s ‘happy hormones’ – serotonin and dopamine – will be released to help lift us out of our winter doldrums.
As therapies to enhance mood and lower stress – such as forest bathing – gather popularity, scientists at the Swedish University of Agricultural Sciences have been carrying out a multi-sensory virtual reality experiment into physiological stress. To the surprise of the research team, the smell of grass, fir trees and mushrooms reduced the stress response more than seeing a forest or park, or hearing birdsong. It seems there’s more to smell than meets the eye. Marcus Hedblom, an ecologist involved in the project, feels we need to know more: “What we really would like to do is go deeper into this and try different types of smell, and try to see which one has the strongest effect.”
At a time when thousands affected by Covid have lost or noticed their sense of smell change, albeit temporarily for most, perhaps a better appreciation for this somewhat overlooked and underused sense is overdue. Maybe National Sense of Smell Day on 24 April gives us the perfect excuse. All we need to do is find a park or wood, smell the flowers, sniff the earth, notice the petrichor, the geosmin, the newly cut grass. Now, more than ever, we could do with lifting our mood and lowering stress with the scents of spring.