Gardening for Health: 2. The Magic of Scent

California wild rose (Rosa californica) has lovely scented flowers

There’s something magical about a scented plant.  The heady fragrance of a wild rose, the musky-sweet scent of four-o-clocks at dusk; or the spicy aroma of a native sage on a warm summer day.  The list goes on and on.  Californians are  blessed with many native scented plants; these make our gardens both unique and interesting.  But the scented plants may also be good for our health!

Plants produce fragrant chemicals for a variety of reasons (most having little to do with human beings).  The sweet fragrances of flowers are released to attract  pollinators.  Some are quite specific – like a perfume designed to attract the right admirer.  Others attract all capable of detecting their sweet scent (native bees, butterflies, moths - even humans).

Likewise, the sweet aromas of ripe fruit attract creatures that can disperse a plant’s seeds.   Unripe fruits are usually unscented – or have a repellant odor.   But ripe fruits can be irresistible, due in part to their attractive fragrance.  Plants have methods of seducing animals to do their bidding, and fragrance is a key weapon in their arsenal.

The scent of native Salvias is related to protection.

The pungent and minty scents produced by some plant’s foliage have a different function: protection.  Dry mediterranean climates support a number of plants with fragrant foliage.  These include some of our favorite cooking and potpourri herbs: rosemary, sage, thyme, lavender, sagebrush and the mints.  To the human nose, these scents are interesting, exciting and attractive.   That’s why we use them extensively in foods, perfumes and other products.

But many of the fragrant herbs have a repellant odor to herbivores.  From larger herbivores like deer and rabbits to the herbivorous insects, the pungent scents provide a cue that this plant is ‘not fit to eat’.  In some cases, the plant just tastes bad; in others, the plants are actually toxic to the herbivores.   It’s not surprising that scented foliage releases its flavors when crushed.  That’s another example of plant thrift – using expensive chemical resources only when needed. 

 

Wooly bluecurls (Trichostema lanatum) has a complex
 aroma that's hard to describe

But what actually produces the scents? Whether released automatically or when crushed, plant scents are due to small, aroma chemicals (odorants) that interact with the sense organs of an animal.   Because they are carried by the air, most aroma chemicals are relatively small.   And the plant-produced odorants have a limited number of basic structures (most are esters, turpenes, aromatics and amines).   But the variants of these basic structures – and their combinations in individual plant species – can produce aromas as varied as the sweet scent of a rose or the putrid odor of the Voodoo lily (smells like rotting meat – attractive only to fly pollinators).

Aroma chemicals interact directly with an animal’s olfactory receptors. In vertebrates, these receptors are located in the nasal passages (the human nose and throat); in insects, the receptors may be located in antennae or other sense organs. But in all cases, odorants bind to and activate the olfactory receptors, resulting in a signal being sent to the brain via olfactory neurons (see below; ref 1).

 

 

And here’s where things get interesting.  In humans, the olfactory neurons (nerve cells) converge at the olfactory bulb, an area of the brain rich in interconnecting neurons.  Signals from the olfactory bulb are sent to at least five different areas of the brain.   Some of these areas are responsible for decoding the scent: does it smell like any other scent?  Is it a known scent?      But there are also close, direct connections between the olfactory bulb and brain structures important for memories and emotions: what is often called the limbic system.

The limbic system is a series of evolutionarily old structures located deep within the human brain. The limbic system supports a variety of functions including emotion, behavior, motivation, long-term memory and olfaction. [2] It is connected to the more modern, cerebral areas of the brain via the hippocampus. There’s still much to learn about how the limbic system works – or even if the concept of a limbic system is obsolete. But the ‘limbic system’ is involved in some of the more interesting aspects of human interactions with aroma chemicals: scent memories and the associations of particular scents with moods and emotions.

Dr Bryan Raudenbush, Professor of Psychology at Wheeling Jesuit University, notes: ‘Of our five senses, scent is the only one with a direct pathway to three important areas of the brain: the orbito-frontal cortex, which presents you with an awareness of scent, the hippocampus, which is associated with memory, and the amygdala, which is associated with mood and emotions.’ [3]

Common wisdom has long associated certain scents with human emotions or physiologic reactions.  For example, the scent of lavender has long been used for relaxation and inducing sleep.   In aromatherapy, the scent of citrus is thought to be a ‘mood brightener’, along with that of rose, heliotrope and peppermint.   But is there any scientific evidence for the efficacy of these scents to alter moods?

Alas, olfaction is the least-researched of the senses.  But there’s good reason to think that scents do affect our moods and physiology.  The ‘limbic system’ can directly activate the hypothalamus, an important hormonal control center in the brain.   The hypothalamus is responsible for the production of growth hormones, sex hormones, thyroid hormones, and neurotransmitters such as serotonin. These hormones affect energy levels and many other physiologic responses.  So it’s reasonable to hypothesize a physiologic role for hormones in the human response to scents.  And scientific studies are beginning to provide the evidence. [4]

 

Each Salvia has a slightly different scent

But there’s even more theoretical reason to suspect a direct role for scent and mood. When we smell something nice, receptors in the amygdala release  dopamine and serotonin. [3, 4]  These are powerful neurotransmitters; the former is linked with the high you feel when taking drugs such as cocoaine, the latter with mood. ‘In a nutshell,’ says Dr Raudenbush, ‘You smell something ‘good’, and those scent chemicals stimulate the amygdala, which in turn prompts the release of dopamine and serotonin, and we feel ‘good’.’ [3]

So scents may directly modulate our moods, via the effects of neurotransmitter and/or hormone levels.  But the picture is further complicated by the close relationship between the olfactory neurons and the hippocampus, which is associated with memory.  This part of the brain helps us ‘remember’ a scent – and its likely consequences (for example: ‘this is the scent of White sage’; or ‘smoke = fire’).   

The ability to identify scents correctly was key to survival in our evolutionary past.  It helped us find food and avoid harm.  Pleasant plant scents may also have played a role in the human-plant interactions leading ultimately to agriculture.  It should come as no surprise that a good sense of smell developed early in our ancestral past.   And that scent memories are different from other types of memories.

Scent memories are among the most vivid, and are often associated with a person or place.  We’ve all smelled a particular brand of perfume and been instantly reminded of a person who used to wear it.  Or smelled a scent and been transported back to the chaparral or woods where we played as children.  Such scent memories are often vivid, specific and long-lasting (even into advanced old age).    And the most vivid scent memories seem to be those associated either with novel scents or with intensely positive or negative feelings coupled with a particular scent.  There’s a reason why the scent of pancakes brings us back to our grandmother’s kitchen!

So, the effect of specific scents on our moods may in part be due to their associations with ‘vivid’ people and events – good and bad – in the past.  And it’s very difficult to tease out the direct effects of scents on human physiology from the indirect effects on moods and emotions tied to scent memories.  In fact, this is an area of active research and current debate. [see ref. 5 & 6, below, for more]

But it really doesn’t matter how scents affect our moods.   In fact, one way or another, they do. The makers of perfumes and the aromatherapy industry have known this all along.  There’s a reason that scented plants have been used to enhance bodies and abodes, in most cultures, for as far back as we know.   Plant fragrances can be used to disguise body odors and other unpleasant smells.  But fragrance also plays a role in human moods, emotions and even social interactions.  The fact that science is beginning to back up these claims is just icing on the cake.

 

 

So how do we apply all this to our gardens?   First, we should remember that the most interest gardens are those that engage all of our five senses.  Most of us think a lot about color and form – the visual elements - when designing our gardens.   And gardens that sooth and heal should be pleasant to the eye.  But the sense of smell is at least as important.   So we should think about scent when choosing plants for our gardens.

Each person experiences a given scent uniquely.  This is due both to physiologic differences and differences in scent memories.  When choosing scent plants, choose ones that make you feel good.  Visit a native plant nursery and ‘try out’ the different fragrances of the native sages (Salvias).  Each cultivar and species is a bit different, so be sure to plant one you like.  Visit Mother Nature’s Backyard.  We have a number of scented plants, and encourage you to experience them fully.  For a list of fragrant native flowers see: https://www.slideshare.net/cvadheim/california-plants-with-fragrant-flowers.   For a list of scented native foliage plants: https://www.slideshare.net/cvadheim/califoria-plants-with-fragrant-foliage.

 

Mother Nature's Backyard & Garden of Health: a great
 place to 'try out' plant scents

 

Place scented plants where you can best enjoy them: near a window, along a path or near an outdoor seating area.   Grow scented herbs in your kitchen garden, in pots on your porch or near the back door.

 

Fragrant pitchersage (Lepechinia fragrans) has fragrant foliage

 

Take time to really enjoy the fragrances in your garden.  Remember to ‘stop and smell the roses’.    Leave your electronic devices inside, close your eyes, and truly experience the fragrance of a rose.  Crush the leaves of a mint, inhale its aroma and be aware of its effect on your breathing, heart rate and mood.   Do you feel relaxed?  Invigorated?  Does your mind feel clearer?

Share your scent garden with others.  Invite your friends to enjoy your garden.  The scents will enhance your interactions like nothing else.   Dry your scented flowers and foliage for use in cooking and potpourri. Be sure to share some of your scented wealth.  For more ideas see: http://mother-natures-backyard.blogspot.com/2016/04/california-gourmet-making-flavored.html and http://mother-natures-backyard.blogspot.com/2013/11/garden-crafts-making-potpourri-from.html.

 

These are challenging times!  It’s no wonder we’re feeling a little stressed!   In fact, we’re in serious need of stress relievers – and the scents of our gardens can play an important role.   So resolve to add some scented plants to your garden this year. You’ll be amazed at the results!

For more posts in this series see : http://mother-natures-backyard.blogspot.com/2018/01/gardening-for-health-1-go-hug-tree-for.html

For several talks on the use of native scented plants, see:

• http://www.slideshare.net/cvadheim/extraordinary-scents-2012
• https://www.slideshare.net/cvadheim/scent-gardens-2018 

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1.       https://blog.cognifit.com/the-sense-of-smell/

2.       https://en.wikipedia.org/wiki/Limbic_system  

3.       https://www.healthista.com/6-scents-will-transform-mood/

4.       https://onlinelibrary.wiley.com/doi/epdf/10.1111/ics.12096  

5.       https://www.scientificamerican.com/article/do-scents-affect-peoples/

6.       http://www.sirc.org/publik/smell_human.html

 

 

 

We welcome your comments (below).  You can also send your questions to: mothernaturesbackyard10@gmail.com

 

 

Love 'Mother Nature's Backyard'? Here's your Chance to Participate.

Help maintain Mother Nature's Backyard through our Gardenista Program

Volunteer at Mother Nature’s Backyard & Gardens

Mother Nature’s Gardenistas

 

 

Overview:  Mother Nature’s Gardenistas are volunteers who help maintain Mother Nature’s Backyard gardens, blog and programs.  The gardens are located in the Gardena Willows Wetland Preserve (Gardena, CA).  For information on the gardens see: https://mother-natures-backyard.blogspot.com/

 

Benefits of being a Mother Nature’s Gardenista

·         Learn about California native plants, their uses and management

·         Meet/network with others interested in water-wise,  life-friendly,  sustainable gardening, and in the local ecosystem

·         Experience regular doses of Nature in a preserve and gardens (good for your health)

·         Share your knowledge and experience with others

·         Give back to the local community, while exercising your mind and body

·         Use your skills and talents, including writing, photography, the arts, teaching, fund-raising and more.

 Requirements:

·         Interest in gardening with California native plants

·         Gardening experience (particularly with native plants) - useful, but not required

·         Commitment of at least one 3-hour block each month (weekday and weekend times available) for a period of at least 6 months

·         Willingness to learn and contribute as part of an active team

·         Curiosity about - and enthusiasm for - the natural world and for gardening

 

What you may do as a Gardenista: 

You will be working under the guidance of an experienced Head Gardener, who will coordinate the volunteer program.  Tasks will vary depending on the season and the skills and talents of the volunteer.  We’ll try our best to match your skills and interests with our needs.  You may be asked to: 

·         Assist with monthly gardening tasks, including: planting, watering, pruning, weeding, etc.

·         Help make decisions on future directions for the gardens & educational programs

·         Serve as a docent during times when the gardens are regularly open

·         Assist with special events like garden tours, workshops, classes

·         Teach classes and workshops in the gardens (depending on knowledge and skills)

·         Write columns for Mother Nature’s Backyard blog and/or serve as blog master

·         Help develop educational brochures and other garden teaching materials

·         Photograph the garden and garden events

·         Give outreach talks to local garden clubs and other groups

  

For more information: contact us at mothernaturesbackyard10@gmail.com

 

 

 

Plant of the Month (March) : Canyon Silktassel – Garrya veatchii

 

Canyon silktassel (Garrya veatchii): 4 year old plant, Mother Nature's Garden of Health

By March, Southern California gardens are greening up and plants are beginning to flower.  We’ve discussed a number of March bloomers over the years.  But the Canyon Silktassel (Garrya veatchii) in Mother Nature’s Garden of Health is finally large enough to bloom; so we’re featuring it as our plant of the month. The scientific name is pronounced: GARE-ee-uh   VEECH-ee-eye.

Canyon silktassel belongs to the family Garryaceae (the Silktassel family). This small family includes but two genera: Garrya and the Asian Acuba (note: some taxonomists place Acuba in a separate family).  Of the 15 or 16 species of Garrya, six are native to California, most with ranges predominantly in Northern California.  The most common species grown in gardens is the northern coastal Garrya elliptica (Wavyleaf silktassel).  There are several well-known cultivars of this species.  

Several Garryas extend south into the mountains and foothills of Southern California. Garrya flavescens (Ashy silktassel) grows in the San Gabriel Mountains and Garrya fremontii (Fremont’s silktassel) in the mountains of Riverside, San Bernardino and San Diego Counties. But of all the California species, Garrya veatchii has the most southerly distribution, typically ranging from San Luis Obispo County to northern Baja California, Mexico. The Canyon silktassel can still be seen in the Transverse and Coastal Ranges of Southern California (including the Santa Monica and San Gabriel Mountains of Los Angeles County).

Canyon silktassel (Garrya veatchii): mature plant

Canyon silktassel (Garrya veatchii): foliage

 

Garrya veatchii grows on dry slopes below about 6000 ft. (1759 m.) in the chaparral and central/southern oak woodland plant communities.  It’s a tough, evergreen plant, often found growing with scrub oaks, Chamise (Adenostema), Threeleaf sumac (Rhus trilobata) and California brickelbush.  It grows as a multi-trunk woody shrub or small tree, ranging in size from 4 to 8 ft. (1.2 to 2.5 m.) tall and about as wide.  The bark is red-brown when young, becoming gray with age. Plants are slow-growing until established (3-4 years) then have a medium growth rate.

Canyon silktassel (Garrya veatchii): leaf

Canyon silktassel (Garrya veatchii): leaf (back)

 

The leaves are one of the best ways to distinguish between the Canyon and Wavyleaf silktassels.  The leaves of Garrya veatchii are simple, evergreen, up to 3 inches (3-9 cm) long  and leathery.  The leaf shape is elliptical or lanceolate (somewhat lance-shaped).  The upper surface is waxy, shiny and medium to dark green; the under surface white with dense hairs.  The leaf margins are straight, unlike the distinctly wavy margins of the Wavyleaf silktassel.  The leaves become darker with age; their margins sometimes roll under in dry conditions.

 

Canyon silktassel (Garrya veatchii): emerging flowers

 

Silktassels are planted in gardens primarily for their unique and picturesque flowers.  Plants generally bloom in winter or very early spring – January to March or April.  The flowers themselves are small and cream or pink-tinged.  But they grow along dangling catkins that are 2-5 inches (5-12 cm) long – lovely in a mature plant.  Plants are dioecious (separate male and female plants) and the males have the longer, showier catkins.  There’s really nothing like a flowering silktassel; a mature plant will stop people in their tracks, wondering what that interesting shrub is.   The dried bracts remain on the plant for several months, prolonging the show.

Canyon silktassel (Garrya veatchii): flowering plant

 

Female plants produce small, egg-shaped fruits if flowers are pollinated.  We’ve got just one plant (sex as yet undetermined); like most gardeners, we’ll never see any fruits.  The plants are wind pollinated.   For pictures of the fruits see references 1-3, below.

Canyon silktassel (Garrya veatchii): development in Mother Nature's Garden of Health

 

In nature, Canyon silktassel grows in full sun or in some shade.  In hot gardens away from the coast we recommend light shade or afternoon shade.  In our garden of Health we’re growing our plant on the north side of a tall wall.  It gets plenty of morning sun and seems to be doing fine.  While silktassels like well-drained soils, ours appears to be fine in a clay-loam.   So any soil other than one with poor drainage will likely work. 

Garrya veatchii tolerates heat, air pollution, dry soils and seaside conditions.  It’s probably a better choice than Garrya elliptica in most Southern California gardens. Canyon silktassel is quite drought tolerant once established.  We planted ours in 2014.  We’ve been watering it 1-2 times a month (deep watering) in dry times.  This summer we’ll probably just water once a month through August or early September.  It’s important to let soils dry out between watering to prevent root fungal diseases.   We’ll play it by ear and update this post if we need to.

Canyon silktassel (Garrya veatchii): pruning to espalier on a wall.

 

Garrya veatchii is often grown as an evergreen shrub, foundation plant or accent.  It can also be used in hedges and hedgerows. Its dark foliage makes a good background for more brightly colored perennials or shrubs with gray-green foliage.  It also makes a wonderful and easy espalier along a wall or fence (see above).   We’re hoping that this will be the year when our silktassel really takes off.  We’re tired of the cinder block wall and look forward to seeing it covered in green!

While not attracting pollinators, mature plants provide good cover for birds and small animals.  The fruits are eaten by birds.   And in the wilds, the foliage is occasionally eaten by larger herbivores (like deer, Bighorn sheep).

The fruits of Garrya species are used to make gray to black natural dyes. The hard wood is sometimes used for carving. And silktassels have a history of medicinal use.  A decoction of leaves is used externally to relive pain from cuts, sores and minor wounds.  The leaves are very bitter and leaf decoctions have also been used as a quinine substitute, especially to lower fevers.  Tinctures are also occasionally used to relax smooth muscle cramps and spasms.   The plant should not be used by pregnant women, as it is thought to induce spontaneous abortion. And as always, medicinals should only be used under the supervision of a health practitioner.   See references 4-6 for more on medicinal uses and precautions.

We hope our discussion and photos will entice you into trying Canyon silktassel in your own garden.  It’s a nice, fairly carefree shrub to grow.  It’s evergreen, with simple dark leaves that provide a nice background.  It’s a useful plant – and one that can be magnificent as an espalier.  We suggest it’s worth a try!

Canyon silktassel (Garrya veatchii): fabulous flowers!

 

For a gardening information sheet see: http://www.slideshare.net/cvadheim/gardening-sheet-eleocharis-macrostachya

For more pictures of this plant see: http://www.slideshare.net/cvadheim/eleocharis-macrostachya-web-show

For plant information sheets on other native plants see: http://nativeplantscsudh.blogspot.com/p/gallery-of-native-plants_17.html

_____________________

1.       https://www.inaturalist.org/taxa/56204-Garrya-veatchii

2.       http://nathistoc.bio.uci.edu/plants/Garryaceae/Garrya%20veatchii/index.html

3.       http://www.smmflowers.org/mobile/species/Garrya_veatchii.htm

4.       http://kivasenchantments.com/silktassel-shining-from-the-shadows.html

5.       http://www.naturalwellbeing.com/learning-center/garrya_leaf/

6.       Moore, Michael: Medicinal Plants of the Pacific West

 

 

We welcome your comments (below).  You can also send your questions to: mothernaturesbackyard10@gmail.com