Why it might be time to give your plants a sniff
By Heather Raithby Doyle
Above: Anise hyssop (Agastache foeniculum). If you are ever in doubt about whether a plant is, say, anise hyssop or the unrelated but similar looking hyssop, try plucking a leaf off and rolling it between your fingers. Anise hyssop will reward you with a delightful black licorice scent. Photo: Elizabeth Georges
There’s no doubt our gardens can be a visual feast. But many native and other plants are aromatic as well, charming our sense of smell. Some experts say smell is our strongest sense, and one that goes straight to the part of the brain associated with emotions and memories (Walsh, 2020). While our sense of smell might decline with age, the good news is we can train our brains by daily workouts. So what better place to sniff than in our native plant gardens?
Not only can we open up our senses by breathing in the aroma, we can marvel at the role fragrance plays in a plant’s success.
The plant’s common names can give a hint as to what our noses will find. Shade loving wild ginger leaves have a faint gingery perfume. Wild bergamot, or bee balm, has a citrusy, minty smell similar to bergamot tea.
Above: Skipper sipping nectar from a fragrant wild bergamot (Monarda fistulosa), a member of the mint family. Leaves are fragrant too, and make an excellent tea. Photo: Peeter Poldre.
Not only can we open up our senses by breathing in the aroma, we can marvel at the role fragrance plays in a plant’s success.
Along with colour, and structure, fragrance is a way plants beguile and entice insects, bees, butterflies and moths to visit them. In exchange for the visit, in which pollination vital to the plant’s future occurs, a reward of nectar and pollen is offered.
The relationship between plants’ fragrance, and pollinators is surprisingly fluid.
Studies show that plants can create a stronger floral fragrance to attract beneficial pollinators in just a few generations of plants (Ramos and Schiesti, 2020). As well, plants will produce floral compounds targeted to a particular insect. This is a win-win situation, allowing insects to recognize the plant and forage more efficiently, which also increases pollination.
“Plants tend to have their scent output at maximal levels only when the flowers are ready for pollination and when it’s potential pollinators are active already,” according to Perdue University Association Professor Natalia Dudareva. Once a flower is pollinated, the plant reduces the scent, thus directing insects to unpollinated flowers.
Plants that attract bees and butterflies in the daytime tend to have sweet smells while beetles find spicy, musty, or fruity fragrances to be more appealing. Smell also proves a powerful way to guide moths and bats to their midnight feasts (Ramos and Schiesti, 2020).
While we humans may pride ourselves on being an advanced species, it is likely insects have a much more acute sense of smell than we will ever possess.
The role of scent is confounding, though, when it comes to herbivores. An odour may repel some critters, but it also unavoidably acts as an advertisement. Plants have adapted to defend themselves against munching herbivores like rabbits in a number of fascinating ways, including creating toxins or digestibility issues, changing their growth season, or adapting with fast regrowth ((Kersch-Becker et al, 2017).
While we humans may pride ourselves on being an advanced species, it is likely insects have a much more acute sense of smell than we will ever possess. There is a whole world of scent in our garden we may never be able to know or even measure. Luckily though, there are plenty of Ontario native plants with intoxicating fragrances that we CAN appreciate that will add a whole other dimension to our garden experience.
So go ahead, get close and give that Joe Pye weed a sniff. Because a Joe Pye weed flower, by any other name, would smell as sweet. It’s no wonder the bees love it. Here are a few more fragrant plants you may want to consider adding to your garden:
Spicebush, used medicinally by Indigenous peoples, has berries that smell like allspice, and bark with a cinnamony aroma. The leaves and twigs also have a spicy smell.
Bee balm with red, showy flowers when crushed smell like Earl Gray Tea.
Evening primrose has sweet smelling yellow flowers that open at night, attracting moths
Sweetgrass is a fast spreading grass with a vanilla scent used by First Nations for ceremonies.
Virgin’s bower, a fast growing native Ontario clematis with sweetly fragrant white flowers.
Swamp milkweed, with longlasting pink flowers has what Lorraine Johnson calls “an intoxicating fragrance of vanilla.” (100 Easy to Grow Native Plants, p 108)
Twinflower makes a nice woodland groundcover, and has fragrant white flowers.
Virginia mountain mint is lovely and minty if you crush the leaves.
Prairie dropseed grass has late summer flowers that smell like cilantro or popcorn, according to Ken Druse in his The Scentual Garden: Exploring the World of Botanical Fragrance.
Sources
Druse, Ken (2019). The Scentual Garden, Abrams, ISBN - 13:9781419738166
Dudareva, N. (2005). Why do flowers have scents? Scientific American April 18, 2005 newsletter https://www.scientificamerican.com/article/why-do-flowers-have-scent/
Johnson, Lorraine (2017 ). 100 Easy to Grow Native Plants, Douglas and McIntyre, ISBN - 13:9781771621441.
Kersch-Becker, Mônica F.; Kessler, André; Thaler, Jennifer S. (2017). Plant defenses limit herbivore population growth by changing predator–prey interactions. Proceedings of the Royal Society B https://doi.org/10.1098/rspb.2017.1120
Ramos, S. and Schiesti, F. (2020). Evolution of Floral Fragrance Is Compromised by Herbivory, Frontiers of Ecology, Vol. 19. https://doi.org/10.3389/fevo.2020.00030
Walsh, Colleen (2020). What the Nose Knows, The Harvard Gazette. https://news.harvard.edu/gazette/story/2020/02/how-scent-emotion-and-memory-are-intertwined-and-exploited/