Our garden plants’ reaction to smoky air

    "No fire is without smoke, nor smoke without fire.” – 13th century France, earliest recorded version of the idiom, “Where there’s smoke, there’s fire.”

    Try as I might, I could not find the particular piece of literature in which this currently apt phrase was first used, but I did learn that by 1592, the English were also using the idiom, similar to the way we say it today, to infer that if something looks wrong, then it probably is wrong.

    Indeed, there are numerous other expressions in which “smoke” is used figuratively: when the smoke clears, smoked out, smoke and mirrors, the big smoke, Holy smoke, blowing smoke, smoking gun and smokin’ hot!

    Little wonder that smoke is so much a part of our everyday language when humans have been affected, positively and negatively, by smoke and fire throughout the ages.

    Similar to humans, plants are affected by fine particles in smoke that consist of ash, partially consumed fuel, water droplets, and hundreds of chemical compounds, including carbon monoxide, carbon dioxide, hydrocarbons, and small amounts of nitrogen oxide. These particles can clog the plant’s stomata, which are tiny pores that enable the plant to absorb carbon dioxide and other gases from the atmosphere and release oxygen. Prolonged blockage can suffocate plants.

    In addition, studies have shown that even short-term exposure to smoke destroys chlorophyll in plants and, thus, reduces their ability to carry out photosynthesis by as much as 50 percent. The result is plants that are stressed, weakened, and may look wilted and washed out. Once the plant has switched to survival mode, fruiting and ripening slows down; prolonged exposure to smoke may also affect the taste of garden produce.

    On the other hand, there are actually some benefits to plants associated with smoke. Smoke reduces the intensity of direct sunlight, which helps to prevent heat stress and sunscald. Smoke diffuses sunlight, and so light reaches plants from different directions. This means lower leaves may capture more sunlight than they would under normal conditions, and are therefore better able to produce food for the plant. Smoke may also provide an advantage to our garden plants by inhibiting fungal diseases and insect activity.

    In fact, plants have been adapting to wildfires and smoke for the past 350 million years. There is evidence that plants use smoke as an environmental cue to initiate defense mechanisms that help them to continue growing and reproducing. For example, smoke activates seed germination in some plant species. The best news is that plants have evolved remarkable resiliency. Once the air clears, our garden vegetation will resume its normal processes, just as we return to our gardening routines. In the meantime, our plants will be benefit if we spray the leaves and fruit gently with water and fertilize to promote healthy roots and foliage.

    About the same time that the idiom, “Where’s there’s smoke, there’s fire” was first published in English, Shakespeare used smoke metaphorically in “Romeo and Juliet.” Romeo tells his friend, “Love is a smoke raised with the fume of sighs … .” Is Romeo describing love as ephemeral, perhaps even painful as when smoke gets in our eyes and makes us cry? Perhaps, but Romeo goes on to note the bad and the good of “smoke”:

    “[Smoke] Being purged, a fire sparkling in lovers’ eyes;

    Being vexed, a sea nourished with loving tears.

    What is it else? A madness most discreet,

    A choking gall, and a preserving sweet.”

    I write about the best plants for cleaning the air this week on my blog at: http://blogs.esouthernoregon.com/theliterarygardener/

    Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at rnowak39@gmail.com.

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