Dr William Foster, Emeritus Curator of Insects, writes:
It is the world of smells that is most cruelly crushed by the cold of winter. Even on the chilliest days our eyes and ears have something to feast on. The bare branches still pattern the sky, the holly berries glow against the glossy leaves, and the blackbirds sing. But for our nostrils the diet of odours is meagre. We feel this loss acutely, even though we are rubbish at detecting smells in the first place. Unlike our dogs, we may not be connoisseurs of conspecific urine, but odours affect us deeply, catching us unawares, and unlocking the gates of memory. On mild winter days, what cheers us most, more than anything we might see or hear, is the delicious fragrance of flowers, the unexpected heralds of spring and of better times to come.
One of the best places in Cambridge for sniffing out some winter fragrance is the Botanic Garden. Head for the Winter Garden area, which both looks and smells good. The nearby Scented Garden is less rewarding in winter and would appear to be keeping its arsenal of smells in reserve for a warmer season. The Botanic Garden is where I first came across the Christmas Box (Sarcococca spp), which you usually smell before you see it, and it is not much to look at in any case: low evergreen shrubs, from whose inconspicuous flowers spills out a warm enveloping smell that floods over the lawns and paths. Perhaps the most powerfully smelling winter plant in the Botanic Garden is Daphne bholua, whose variety “Jacqueline Postill” is grown extensively in the borders. It is immediately obvious where the smell is coming from, since this is a medium-height shrub covered in late winter with a mass of showy pink flowers. Daphne is named after a minor Greek goddess who preferred to be transformed into a tree rather than submit to the unwelcome attentions of Apollo.
The winter-flowering honeysuckle (Lonicera fragrantissima) has loads of warmly-smelling white flowers, although it is a rather straggly, untidy shrub. Not everyone likes Mahonia, of which there are several species, including the Oregon Grape, with its saturated yellow and sharply smelling flowers, but it is splendidly reliable and lights up the winter garden. It is named after the early 19th century Irish-American botanist Bernard McMahon, whose patrons included Thomas Jefferson and Benjamin Franklin. It is nevertheless a rather unyielding plant, for many people appreciated best when in someone else’s garden.
Several small low-growing plants are also deliciously scented but you may have to kneel down to savour them fully. If you can still do this without military assistance, I would recommend some of the snowdrop cultivars, of which the Botanic Garden has a spectacular display. Try “Magnet”, which has large nodding sweet-smelling flowers borne on slender, arching pedicels. Sweet violet (Viola odorata) has a good smell but this does require almost complete prostration.
Not all the fragrances produced by these winter-flowering plants are pleasant. The Western Skunk Cabbage (Lysichiton americanum), a member of the Arum family, grows by the streamside in the Botanic Garden and its bright yellow flowers produce a strong musky smell to attract fly pollinators.
One might wonder why all these plants bother to provide fragrances in winter, since pollinators are usually in very short supply. Are these flowers, in the words of Gray’s Elegy, wasting their “sweetness on the desert air”? Undoubtedly this is true for some of the plants transported to our gardens from lower latitudes, such as southern China, by plant-hunters in the past. But several of these garden plants occur naturally in colder regions. There are, for example, two species of Daphne (mezereum and laureola), which occur wild in the British Isles. I remember the excitement of finding D.mezereum, flowering in a cold limestone woodland in Craven: botanists are always very careful not to reveal the sites of this plant, lest they be dug up by enthusiastic gardeners.
If you look closely at many of these scented flowers on mild winter days, you will often see a surprising number of insect pollinators. Big furry bumblebees, the workhorse pollinators of plants of the arctic, are probably the commonest, along with honeybees, other non-social bees, and a range of flies, particularly hoverflies. It had long been assumed that bumblebee colonies die off in the winter and only newly mated queens survive, emerging every so often on warm days for a top-up of nectar. It is now clear that in urban areas whole colonies can keep going, with workers foraging on pollen and nectar throughout the winter months, often at even higher rates than they can manage in summer. They depend on flowering shrubs, with Mahonia seeming to be the most important, at least in the London area.
Some of these winter-flowering plants have cunning tricks, in addition to their scents, to lure in the pollinators. If it gets warm enough, snowdrops open their outer petals, like ballerinas performing pliés, to give bees easier access to their nectar and pollen. Some flowers turn towards the winter sun and have petals that reflect the sun’s rays into their centre to warm themselves and their insect visitors. Most cunningly of all, the skunk cabbage is able to generate its own heat – enough to melt the snow around the emerging inflorescence – which projects its skunky odour into the wintry air, luring any passing flies into its warm embrace.
The universal appeal of fragrance in winter is encapsulated in the nativity carol “D’ou est cette odour agréable” which I used to sing enthusiastically as a schoolboy treble. I was intrigued by the word “whence”, by the paradox of an agreeable odour (boys are generally more familiar with disagreeable odours), and by the puzzle of the source of the smell. It seemed unlikely to me, as a farmer’s son, that an agreeable odour should come from a stable. Perhaps it came from the Frankincense, Caspar’s gift, but it shows that, in the depths of winter, we yearn for fragrance as well as light.