Fresh Start 2021: Carbon Garden

October blooming Camellia sasanqua

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Only recently have I come across the term ‘Carbon Garden’ in the current issue of Horticulture Magazine.  You may be ahead of me on this one, but the picture that came to mind when I first saw the term wasn’t very pretty.  The reality of it is much more attractive, and this garden style proves easier to maintain than many other garden styles.

Like other elements, carbon is an atom that can manifest as a solid, in a liquid, or as a gas.  Carbon dioxide (CO2) and carbon monoxide (CO) remain in the news because they contribute so much to our warming environment.  Gasses like carbon dioxide and methane (CH4) trap heat from the sun near the surface of the earth, causing warmer weather and heavier rainfalls.  Conversations around reversing the current warming trends usually focus on reducing carbon emissions and finding ways to scrub carbon out of the air.

Magically, we have living tools for removing carbon from the air right outside our windows.  You see, every green plant cell uses carbon dioxide in its daily efforts to feed itself and sustain the entire plant.  In the presence of sunlight, carbon dioxide and water transform into glucose, used to power plant growth, and the waste product oxygen, which of course we need in every breath.

When you contemplate a leafy tree, imagine each leaf inhaling polluted air and transforming that air into pure food and oxygen.

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Japanese Maple

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Glucose is further transformed into cellulose, which structures the cell wall of every plant cell.  Now, imagine a tree’s roots growing deeper and wider into the earth with each passing year.  What are those roots made from?  Cellulose:  largely, carbon.

A tree, and most any other plant, can stash carbon deep underground where it will remain for many years in solid form.  Many plants also store nitrogen, filtered out of the air, on their roots.  In fact, any plant in the pea family stores little nodules of solid nitrogen along their roots.  Knowing that nitrogen is a major component of fertilizers, you understand how this stored nitrogen increases the fertility of the soil in the area where these plants grow.

Plant leaves are also made primarily of carbon.  When the leaves fall each autumn, they hold stored, solid carbon.  If returned to the soil as compost or mulch, the carbon remains stored, or sequestered, in solid form in the soil.  This is how ordinary garden soil may be transformed into a ‘carbon sink.’

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Turkey tail mushrooms help decompose the stump of a fallen peach tree. Leaving the stump in place and allowing vegetation to cover it conserves its carbon in the soil.

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A log is made largely of stored carbon.  When you burn it in the fireplace, those chemical bonds break down, and much of the carbon rises back into the air as smoke.  If the same log is made into a cutting board or other wooden object, then the carbon remains in sold form.

Just as burning can break chemical bonds to release carbon back into the air, so will decomposition.  We’ve come to understand that bare dirt, including tilled fields and gardens, releases carbon back into the air.  But ground covered by mulch or living plants doesn’t allow that carbon to move back into the air.

All of this helps explain the science behind the principles of Carbon Gardening, whose goal is to scrub as much carbon as possible out of the air and sequester it in the earth.  Forests have done this very efficiently for untold ages.

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Only in recent times, with so much natural forest cleared and land exposed, has our planet begun its dramatic warming.  Think of all the carbon stored over the centuries as coal, petroleum, peat, and held close under a forest canopy that has been released into our atmosphere over the past century.

So, the point of Carbon Gardening is to use one’s own garden to sequester as much carbon as possible, using gardening methods that hold the carbon in the soil, without burning or releasing any more carbon than possible in the process.

Every breath we exhale contains carbon dioxide.  Our cells produce it as they produce energy.  We live in harmony with the plants we grow, taking in the oxygen they exhale while giving them back our own carbon rich breath.  That said, please don’t try to hold your breath as you make your Carbon Garden.

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Camellia sasanqua

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Here are a few principles of Carbon Gardening that may help point you in the right direction. 

The Audubon Society has a series of articles that go into far more detail.

  1. Plant intensely in layers:  The more plants in growth the more carbon will be scrubbed from the air each day.  Trees are most efficient because they support a huge volume of leaves.  Include evergreen trees that continue respiration through the winter months, and plant a shrub layer, perennial layer, and ground covers under the trees to maximize the amount of carbon absorbed by your garden.  Evergreen perennials and ground covers continue absorbing and storing carbon through the winter months.

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  1. Feed carbon (and nitrogen) back into your soil with plant materials. Use wood chips, bark, and shredded leaves as mulch to minimize bare ground.  Remember that roots sequester a large amount of carbon and nitrogen, so leave those roots in the ground.  Cut weeds or spent annuals at ground level instead of pulling them up.  Compost trimmings and leaves, kitchen waste, and unneeded cardboard, newsprint or brown paper.

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This is a very thin layer of compost covering collected branches, bark and leaves from our fallen tree.  We added additional layers of organic material to build the new planting bed.

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  1. Instead of tilling soil and exposing stored carbon, sheet compost in the winter to prepare for spring planting. Cover the garden area with cardboard or paper to protect the soil and smother any weeds.  Build up layers of composable materials, or even bagged municipal compost, and allow it to decompose in place so that planting seeds or transplants in the spring is possible without tilling or excessive digging.  Coffee grounds, tea bags, rinsed eggshells and other kitchen scraps can be ‘buried’ in the layers of a sheet compost pile, but be careful not to discard of seeds in this way unless you want them to sprout in the spring.

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Paper grocery bags covered with several inches of compost smother weeds and soften the ground for this new planting bed, eliminating the need to dig the area up first.  Pea gravel helps hold this area, which is on a slope.

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  1. Remain mindful of garden ‘inputs’ that burn carbon. This includes garden equipment that burns gas, commercial fertilizers, and maybe even those fun trips to the garden center….?

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This bin of new Caladium bulbs was ready to be planted out in mid-May.  Ordering bare root perennials, bulbs, tubers and seeds and starting them at home reduces the carbon footprint of a garden.  The red leaf is C. ‘Burning Heart,’ a 2015 introduction from Classic Caladiums in Avon Park, FL.

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  1. If you normally buy flats of annual plants each spring for pots or borders, consider how to plant those areas more sustainably. Consider all of the carbon releasing ‘inputs’ required to produce those plants, including the plastic containers they are grown in, the transportation to move them, and the chemical fertilizers and peat based potting soil used in growing them.  While all plants sequester carbon from the air, commercial nursery production of short-lived plants releases carbon into the atmosphere throughout the process and should be considered by conscientious gardeners.  What can you raise from seeds, cuttings or divisions, or obtain through trade with gardening friends?

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Saxifraga stolonifera is an evergreen ground cover that is easy to divide and share.  It grows here with Ajuga ‘Black Scallop,’ Hellebores and ferns.

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  1. Choose native perennials or ones that will naturalize in your climate, so your plants spread and reproduce, reducing the number of plants you need to buy each year to fill your garden. Design a sustainable garden that grows lushly with minimal ‘inputs’ and intervention from the gardener.  Native and naturalizing perennials won’t need much watering during dry spells, will make do with nutrients in the soil, and will expand and self-seed.

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  1. Woody plants sequester carbon in their roots and branches and live for many years. These are the most efficient Carbon Garden plants.   A garden made mostly from trees, shrubs, perennial ferns and groundcovers, will work most efficiently.  Some more arid areas have great success with long-lived succulents.  Consider replacing turf grass with plants that don’t require such intense maintenance.

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Mountain Laurel blooms each May, is native to our region and forms dense clumps over time.

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  1. Use the I-Tree Tool to educate yourself about the power of trees in your landscape to sequester and store carbon, reduce run-off and scrub other pollutants out of the air. Use this tool when selecting new trees to plant in your own yard.

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From left: new leaves emerge red on this hybrid crape myrtle, small Acer palmatum leaves emerge red and hold their color into summer, red buckeye, Aesculus pavia is naturalized in our area and volunteers in unlikely places, blooming scarlet each spring. In the distance, dogwood blooms in clouds of white.

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‘Carbon Gardening’ can make a significant contribution to scrubbing carbon out of the atmosphere and sequestering it in the earth, and the total contribution multiplies as the plants grow and the garden develops year to year.  A fully grown native tree can removed fifty or more pounds of carbon from the air annually.  While the amount varies by tree species and size, every year of growth increases the tree’s effectiveness.

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Each gardener who adopts sustainable practices makes a sizeable contribution to off-set and mitigate carbon production in their area.  Planting more plants and allowing them to grow densely also helps manage rainfall so it is stored onsite, rather than running off so rapidly.  The plants sustain wildlife and build a richly integrated ecosystem.

We reduce our own annual costs for new plants, fertilizers, other chemicals and fuel, while also reducing our time invested in garden maintenance.  It is a good approach for any of us who enjoy watching nature weave her tapestry each year, sustainably, while knowing that our gardens are part of the solution to climate warming and climate change.

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Woodland Gnome 2021

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Please visit my other site, Illuminations, for a daily photo of something beautiful and a positive thought.

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