The Scentual Garden: Exploring the World of Botanical Fragrance

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THE INVISIBLE GARDEN

When I come across a beautiful flower, the first thing I do (after checking for a bumblebee) is lean in to sample its smell. If there is no perfume to share, I find the blossom somewhat lacking. Flowers with fragrance create a full experience. Stroking an herb’s leaf, or just brushing against an aromatic plant spilling into the path, transports me to a richer world.

But how many of us consciously take that powerful potential into account when we’re shopping or designing? Botanical fragrance is exhilarating though, sadly, often underutilized. And no wonder, since we gardeners are barely acquainted with the complex dimensions of scent.

I thought I knew quite a bit until I dived into the adventure that resulted in The Scentual Garden.

When describing a species or variety, most catalogs and reference sources will simply say “fragrant” when scent is a factor. I wanted to know more and say more, and that’s the goal of this book: to describe the way plants smell. The problem may lie not in distinguishing scents when we meet them but in lacking the vocabulary. We’ve named a thousand colors, for instance, from scarlet to puce. But words to categorize plant fragrances are hard to come by.

To fill this gap in our botanical knowledge, I’ve created a guide to fragrant plants, grouping them into twelve master categories by scent (see this page). The categories I developed are to some extent informed by perfumers’ classifications but adjusted for the garden and my own nose—a subjective point of view. (Depending on the source, the descriptive olfactive perfume “families” include green, fruity, citrus, herbal, floral, woody, musky, and oriental.)

Most plants have a blend of odors. I’ve picked what I perceive as the primary scent of each plant as my organizing principle; others’ perceptions may differ. And by broadening the vocabulary that I use to describe different plant scents, I hope to evoke the enormous range of associations that they arouse in us.

I suppose some gardeners think plants should be left to speak for themselves: Roses smell sweet. But what about when the garden beds are covered with snow? Or when we try to tell a friend about a plant when he or she is far away, or describe how a plant smells in a book or catalog or to the visually impaired? Even seasoned gardeners can be at a loss for descriptive words. For instance, what do lilies smell like?

Part of my aim in creating The Scentual Garden was to go beyond “fragrant” and “sweet.” Is the fragrance strong or faint? Is the smell sharp or sour? Does the scent of a newly opened blossom change when the blossom is fading? Can you describe it? For the most part, you’ll think of analogies. What does the aroma remind you of? Caramel, pine, clove, or Twizzlers?

I recently sampled flowers all around a Magnolia × loebneri ‘Merrill’ tree in full bloom, for example. The fresh white starburst flowers smelled clearly of citronella. But the older, fading blossoms, with decaying petal points tinged brown, smelled like cola. “Fresh,” “delicate,” “decaying,” “citronella,” “cola,” “butter”—these descriptive words tell me more than “sweet,” and they, with the added factor of time, create a four-dimensional image of what the plant looks and smells like.

This book advocates that you expand your lexicon, and your scentual catalog, starting on a new path of paying added sensory attention to each plant choice. Putting aside color or form or texture, can we close our eyes and let our noses lead us to create more dynamic, exhilarating gardens for all seasons? Fortunately, there is something to smell and restore the spirit in every month of the year. There are flowers, leaves, and even twigs to gather outdoors from late winter through fall, and fragrant plants indoors at the windowsill or in the greenhouse. These days, there are scented cut flowers from the florist or supermarket in just about every town year-round.

Images — **Clockwise from upper right:** White *Magnolia denudata*; pale yellow M. ‘Pristine’ buds; pink M. × *loebneri* ‘Leonard Messel’; open star magnolia M. × *loebneri* ‘Merrill’, which initially smells of citronella but fades to cinnamon and cola.

I’ve written books on gardening and taken photographs that I hoped would communicate what I see. But I haven’t had an opportunity to share what my nose knows, until now. In this book, I do my best to describe botanical smells and recommend fragrant plants to collect. Of course, I couldn’t include every scented plant. After all, there are thousands of fragrant rose varieties alone. But I’ve brought together hundreds of flowers, shrubs, and trees. In my own photos, these species and varieties are shown where they grow, and, in her glorious photographs created on a flatbed scanner, my collaborator, Ellen Hoverkamp, helps you feel what it might be like to meet these plants up close and personal.

Some smells have a profound effect on me. I crush a leaf of mountain mint, for instance, and sniff its strong menthol smell. It’s a clear, clean, supercharged, stimulating wake-up call that opens my nasal passages. Sniffing some flowers is calming and lowers my blood pressure, helping me to relax. Hospitals have found that the smell of vanilla may reduce stress during diagnostic procedures—it sounds good to me. Perhaps we can start to think of gardening with fragrant plants as the ultimate version of aromatherapy.

THE NOSE OF THE BEHOLDER

I have a keen sense of smell, which I jokingly call a blessing and a curse—a blessing in the garden, and a curse on the subway in August. I wouldn’t trade my heightened ability, my hyperosmia, for anything, but that doesn’t mean there aren’t gaps in my perception. Perhaps I smell too well, and something that, for others, is in the background of a plant’s scent is in the foreground for me. That’s my only excuse for not finding the famed scent of sweet pea flowers transformative.

One April day, I was with friends in a greenhouse at Wave Hill, a public garden in the Bronx, in New York City. There was a special heirloom sweet pea blooming, and everyone was cooing. I asked for descriptions of the scent. I heard rose, freesia, orange blossom, hyacinth, grape, jasmine, vanilla, lemon, and freshly mowed grass. To me, the flowers smelled a little bit like honey, but more like dust and baked potato.

A sense of smell can be individual, and scents are subject to personal taste (I know plenty of gardeners who like the smell of boxwood foliage when the sun is on the leaves or when the aroma is released as they brush past the shrub, but many do not, and how someone describes this smell will be influenced by whether she or he likes it or not). For the most part, a keen or a dull sense of smell is in the genes. And the ability to detect odors can be diminished or lost as a consequence of injury or disease, resulting in anosmia—the loss or impairment of the sense of smell.

It’s said that women have a more acute sense than men do, and recent research that has attempted to explain why has identified twice the number of neurons and glial cells in women’s olfactory organs as in men’s, though it’s not yet clear that this offers a biological advantage. It could simply be that women tend to be more attuned to their environment.

I love to have a natural scent around me. I’ve got a sachet of lavender in my car to rub when I feel like it. I’ll cut a fragrant flower and stick it in my pocket (short of a buttonhole) or just lay it on the dashboard when I am off to run an errand. Many flowers remind me of things in the past, and I try to make new scent memories whenever I can and help others to do the same.

When children come, I’ll pinch a scented geranium or a peppermint leaf, a gardenia or jasmine flower, for them to hold. Such simple pleasures can be surprisingly enthralling, and create a moment that they may never forget. When adults visit the garden and one or another flower presents the opportunity, I like to ask them to describe the scent in detail. Try this challenge in your garden. You’re guaranteed a spectrum of responses, ranging from an evocative description (if pressed) to the all-purpose “sweet.”

SMELL: A SUBTLE SENSE

Humans may not be as sensitive to odors as dogs and many other animals, but we’re still no slouches when it comes to detecting smells. Plants’ fragrance comes largely from volatile organic compounds (VOCs) in their oil glands. As these chemicals evaporate, molecules are released into the air, causing scent. Each plant has a mixture of VOCs that make up its unique fragrance. The perfume of a rose flower, for example, is made up of scores of chemical compounds including rose oxide and beta-damascenone. Rose oxide can be detected by our finely attuned human noses in concentrations as low as 5 parts per billion. We can smell beta-damascenone, a typical floral fragrance, in even smaller amounts: 0.009 parts per billion. To give you an idea of what this means, if 1 part per billion were measured in time, it would equal one second in 31.7 years. Despite being present in minuscule amounts, these compounds are readily perceived by our olfactory organs.

When an odor excites a neuron in the nose, an electrical signal travels along the nerve cell’s axon to neurons in the olfactory bulb. This structure, located at the base of the front of the brain, is the clearinghouse for the sense of smell. From the olfactory bulb, odor signals are relayed within the brain to both the higher cortex and the limbic system, which generates emotional feelings and is where memories are stored. This may explain why odors trigger, to borrow a phrase from Marcel Proust, remembrance of things past.

The biological explanation of how we recognize odors is extremely complicated and contentious, with conflicting theories about how the receptor neurons in our noses, when stimulated by similar molecules, distinguish complex odors from one another. Some molecules even produce different odors depending on whether or not they flood the nose’s receptors. Take indole, an organic compound found in jasmine, orange blossom, paperwhite narcissus, and many other flowers. An intense whiff smells foul, while a trace is perceived as flowery. Indole is also found in coal tar, decomposing shrimp, and hyacinth flowers. The next time you sample a strongly scented flower, think of mothballs. You’ll be surprised how often that odor can be detected. But, despite that somewhat unpleasant note, indole is used in perfumery.

Daffodils are the quintessential examples of the indole paradox. Narcissus jonquilla, the species jonquil, has indole in the flower, and yet it is considered among the most sweetly fragrant in the genus. Another narcissus, N. ‘Actaea’, is a poeticus type, with a flat white flower whose small yellow cup is rimmed in red. From a short distance, the smell is one of honey and honeysuckle, but up close there are traces of black pepper and cow dung.

Ellen scanned a daffodil that she described as smelling like gardenia, baby-doll plastic, and mothballs. I’ve smelled mothballs and, sometimes, excrement. Indole is in fecal matter, too, and you can sometimes detect that in the smell of the paperwhites and the more pungent daffodils.

In doing research for this book, I came across several claims that specific flowers had no fragrance. In some cases, I had to disagree. One highly regarded botanical website described the multi-flowered carnation cousin Saponaria officinalis, sometimes known as soapwort or bouncing bet, as having no scent. These scientists should have stayed after work for a few minutes, because soapwort begins to smell around five o’clock in the evening, and it is not a subtle fragrance, either, at least not to me. The flowers may smell like honey, patchouli, lily, strawberry candy, clove, and the telltale mothballs.

When I am in the garden in late winter and early spring, I can smell the intense honey fragrance of blooming puschkinia flowers, Puschkinia scilloides var. libanotica, the striped squill, from twenty or thirty feet away. I asked Ellen to scan some cut ones, and, to her nose, they didn’t smell at all. We discovered that, about a half hour after having been cut, puschkinia stop smelling.

Plants, of course, didn’t evolve their scents to perform on a human schedule, or for our benefit—though I, for one, am enormously grateful to be an unintended beneficiary of their fragrant bounty.