Under the Glass: News from the Greenhouse

Published: January 31st, 2020

Category: Articles

Leah DiehlOne of the sensory tools we use in horticultural therapy is smell. I’ve been appreciating this tool a lot recently because one of my favorite fragrant orchids is blooming in the greenhouse right now.

Have you ever been walking along when all of a sudden you catch a scent in the air that triggers a memory? It might happen when you smell something cooking in a restaurant that brings you back to a time from your childhood in your family’s kitchen. Or when you’re walking through a garden and come across a particular fragrance that transports you back to your grandmother’s garden. This is called a Proustian memory: in the opening chapter of Marcel Proust’s novel Swann’s Way the narrator is overcome by the scent of a madeleine biscuit dipped in linden-blossom tea that brings forth a rush of memories about a long-forgotten childhood event.

Many of our senses can trigger memory: the sight of something in the attic you haven’t seen in decades; hearing a song that you haven’t heard since your wedding day; even the touch of something like a fabric that reminds you of your grandmother’s linens – these are all sensory routes to memory. The thing that distinguishes the experience of evoking a memory based on smell is that of all the senses, smell is tied more closely to emotions. When you trigger a memory based on a smell, it tends to bring with it a flood of emotion – and sometimes intense ones.

Why is that? There is a direct neurological connection between olfaction and emotion processing, which takes place in the limbic system of the brain. The ability to experience emotion grew directly out of the brain’s ability to process smell. If you look back at the development of living beings you can see this – smell was the first sense to evolve and it was needed to survive; for locating food, avoiding predators, and reproducing. Smell was the key form of communication.

Even today when verbal and visual communications are our primary tools for navigating the world, we still react automatically and immediately to smells in our environment. For example, what do you do when you you’re visiting a garden and come across a wonderful fragrance in the air? You go find what flower is producing that scent so you can be closer to it. What about when you open a container of spoiled food in the refrigerator? You physically recoil, and then immediately dump it in the garbage or compost. When we come across an odor in a space, we immediately like or dislike the odor and that determines whether we choose to approach or avoid. Through smell, and our emotional response to it, we are better positioned to react appropriately to the environment.

We often, for good or bad, make assumptions about people based on how they smell. That’s what the perfume industry relies on: creating fragrances that are enticing, romantic, relaxing, exciting – whatever mood you’re in the mood for, or whatever mood you want to project. In a recent study, men thought that women who were wearing a citrus floral scent or a lily of the valley scent weighed on average 12 pounds lighter than they actually did. Now that’s interesting (and useful…).

Smells can affect our mood, stress levels, sleep, self-confidence, and even our cognitive and physical performance. The particular smells we respond to, however, can be different for men and women. So by understanding which scents we respond to we may be able to enhance our health and well-being. Memory can be enhanced if the learning is done in the presence of a certain smell and then that smell is present again at the time of recollection. And interestingly, women are better smellers than men and remain better smellers over the course of their lives (although I’m not sure that’s an advantage all the time – certainly not at my house). Unfortunately, smell function drops off dramatically in the late 50s for men, and late 60s for women.

And finally, keep in mind that fragrance only has an impact if you are not experiencing it all the time. If you are surrounded by the smell of a particular tropical flower all day, its effects are going to diminish. You’re not going to have a strong emotional memory trigger by a fragrance you smell regularly. Our sensory organs are designed to detect changes in the environment, not to monitor constant input –so our senses must receive changing stimulation in order to function.

As gardeners, plant lovers, and horticultural therapy practitioners we are fortunate to be around plants and in nature because both provide sensory stimulation in so many ways. A garden is, of course, a multi-sensory environment that changes yearly, seasonally, monthly, and even daily. The garden impacts all of our senses but, for most of us, its ability to trigger our olfactory sense may have the most impact on our mood and experience in nature.

Elizabeth “Leah” Diehl, RLA, HTM
Lecturer, Dept. of Environmental Horticulture, College of Agricultural and Life Sciences
Director of Therapeutic Horticulture, Wilmot Botanical Gardens, College of Medicine