Six on Saturday: Beating the Heat

We learned this week that July 2021 was the hottest month on record for planet Earth.  Ever. 

That has certainly been true for us here in coastal Virginia.  Even after a lifetime of Virginia summers, I’m looking for ways to adapt to the intensity of our heatwaves this year.  When I go out at sunrise to load my car for a few hours work at our local botanical garden, I am already ‘glowing’ with perspiration before I can get the air turned on in the car.  We have been waking up to temperatures already nearly 80F.

The planet is growing dangerously hot for humans, and it is also growing too hot for many of our favorite plants.  This summer, the sun has been so intense that I’m moving ‘full-sun’ loving plants into partial shade.  Long-time favorites just aren’t thriving and blooming as they have in past years.  They grow stressed even with near daily watering.

Caladiums and many ferns thrive in heat and humidity, so long as they have the water they need to remain hydrated.

As gardeners, we find ways to adapt.  We’ve been blessed with fairly steady rain, but in many parts of the United States struggling with drought, gardeners have limits on water available for irrigation.  And water evaporates from plants and from soil more quickly as temperatures rise.

As climate continues to shift and weather patterns change, we can choose plants that manage to thrive in our changing conditions.  But we can also use plants to ‘change’ the conditions in our own yards and gardens.  We can use plants to help improve the atmosphere in our community.

The greatest agents of change are trees.  They provide three critical services to help mitigate climate change.  First, they offer shade.  Shade helps mitigate ‘heat islands’ along streets, in parking lots, and around our homes.  A tree’s canopy absorbs the sun’s rays to use in making its food and prevents those rays from making it to our roof, our walls, our driveway and street.  It can keep an area several degrees cooler than unshaded areas nearby.  When a neighbor cut a huge old oak tree in their front yard a few years ago, our whole end of the street felt hotter and fiercer on summer afternoons.

Colocasia ‘Blue Hawaii’ grows with Euphobia, a Japanese holly fern and Caladiums. Evergreen plants continue to scrub pollution out of the air through the winter months.

It is far healthier to garden in the shade.  It is cooler, and we aren’t absorbing as much solar radiation into our bodies.  It is safer for our skin and eyes to work in the shade than in broiling sun.  Farm workers, landscapers, and other workers have really struggled this summer, working out in the full sun on such hot days.

As a tree’s canopy absorbs sunlight, each leaf also filters the air.  Greenhouse gasses like carbon dioxide, methane and various elements like nitrogen are absorbed by each leaf and metabolized into sugars and other molecules used by the tree.  Pure oxygen and water vapor are released back into the breeze.  We feel good working under trees because they are scrubbing the air we breathe and filling it with fresh oxygen.  Trees also pump enormous quantities of water out of the ground with their deep roots, and release it into the air, making their surroundings more humid.  Clouds can form over what was once desert, once enough trees have been planted.

What do trees do with the carbon-based sugars they manufacture each day?  They store them up in their own bodies.  Trees build out their branches, widen their trunks, reinforce their roots and produce new leaves with the cellulose-based cells they build each day.  Every plant cell is surrounded with a stiff wall of cellulose, and certain plants, like trees, have tougher cell walls than others.  All of the carbon used in making that cellulose is removed from the atmosphere indefinitely.  A tree may live for hundreds of years, keeping that carbon locked in its branches, roots and trunk.   Each year’s fallen leaves may enrich the soil, keeping the carbon and other elements locked in the Earth.  That is, if we can just leave them be as mulch or transform them into compost.

Woody Lantana, ‘Chapel Hill Gold’ and Salvia ‘Mystic Spires’ thrive in full sun at the Williamsburg Botanical Garden. They shrug off the heat even as they feed bees, butterflies, hummingbirds and other small animals.

Along with the news about our hottest July ever this week, I found a study completed a few years ago in Richmond, Virginia, measuring which parts of the city were relatively hotter or cooler than others.  Volunteers traveled around town with a heat sensor attached to their bike or car morning, afternoon and evening over several days to collect the data.  They produced a map of the entire area showing how much each area heated up between early morning and mid-afternoon and how quickly they cooled off in the evening.  The maps made plain how much difference street trees and home landscaping make in keeping a neighborhood livable.  Those areas that weren’t landscaped, with more paved area, showed the greatest degree of daily heating and the least cooling at night..

Many communities understand the importance of trees to the quality of life for their residents, and now have ‘urban foresters’ on staff to supervise efforts to plant more trees in parts of the community that need them.  Many also have codes that require woody landscaping around new construction of roads, shopping centers, homes and commercial buildings.  The number of trees in a neighborhood often reflects the economic circumstances of the residents, and measurably affects their quality of life.

Wild grapes wind their way through our dogwood tree, creating more shade and feeding wildlife

Planting may be the single most effective thing that any of us can do to make some contribution to improving our community, mitigating the heat in our area, cleaning the air, and keeping our planet habitable.  Whether we are planting trees or ferns, flowering perennials, succulents or crops; every effort helps.  Even kelp in our oceans absorbs and sequesters huge amounts of carbon each summer.

Since trees take many years to grow, the tree I planted this spring may not grow large enough to make a measurable difference for several years.  I rely on a variety of different plants to shelter, cool and beautify my summer garden.  Various vines, including wild grapes, scramble through our trees and over trellises.  Plants with huge leaves, like Alocasias, Colocasias, Canna lilies and Caladiums produce shade for other plants under and around them.  All of these thrive in heat and humidity.   

Large, sun tolerant evergreen ferns provide many of the same benefits of a tree, but on a smaller scale.  They can’t shade my street, but they certainly shade and protect the beds where they are planted. Large leaf succulents, like Yucca, grow in hot, dry sunny areas where other plants might fail, cleaning the air and offering some limited shade.

The plant kingdom holds uncounted solutions to the pressing challenges of our age.  Our personal challenge is to think creatively about how we use plants to benefit ourselves and others.  Our gardens can give us more than just beauty.  They can help preserve our planet.  Humans began their sojourn on Earth in a garden.  Perhaps by continuing to make and tend gardens, we can also insure our survival.

Trees line the paths at the Williamsburg Botanical Garden, creating a cool and peaceful place to shelter this summer.

With appreciation to The Propagator, who hosts Six on Saturday each week.


  1. Is there any natural process other than photosynthesis that takes CO2 out of the atmosphere and releases oxygen back? We are totally dependent on plants yet most of us barely notice them. I despair of all the valiant planting schemes that people get involved in while existing trees, woods and forests are being razed with no one able to stop it. The capacity of plantlife to restore a balance, even if we totally stopped using fossil fuels, is diminishing by the day, all too often going up in CO2 rich smoke.

    Liked by 1 person

    • Jim, I agree with you. We lost several dozen trees in our neighborhood this winter to a corporation clear cutting their pipeline that runs through the community. No effort, including working with local government, was able to stop them. Their procedures were permitted under Federal law on their easements. At the same time, widening an interstate, and other roads, through our county destroyed thousands more trees. When this sort of devastation is sponsored and paid for by government and large corporations, it is hard. All any of us can do is to do what we can, where we are, with what we have. Nothing else matches the efficiency and design of plants to scrub and refresh our atmosphere, sequestering pollutants in solid form. And of course trees are the most efficient plant with a relatively small ‘footprint.’ At least there are lots of efforts now to scrub carbon out of the air by growing various sorts of plants- like sea weeds- and using them for profitable purposes. One of the greatest producers of greenhouse gasses are farm animals. Anyone truly serious about addressing the climate crisis needs to also reduce (or eliminate) use of animal products…. as they also support reforestation efforts.


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