Monday, November 11, 2019

Sequester this carbon! Don't throw it away.

Sequester this carbon! Don't throw it away.
Carbon sequestration is tremendously important because keeping the CO2 levels low in the atmosphere will help keep the earth cooler. It’s the most abundant greenhouse gas.

As I found in doing the research for the Soil section in "Climate-Wise Landscaping," soil sequesters four times more carbon globally than all the terrestrial plants added together, including rainforests. It varies by region and soil type with the peat bogs doing much of the heavy lifting.

Known peatlands only cover about 3% of the world’s land surface, but store more than 30% of the world’s organic soil carbon. Peat or peat moss can never be sustainably harvested because once disturbed, much of that sequestered carbon will be released into the atmosphere. (Peat moss is never sustainable) So we should use other sources of humus for our gardens and landscapes. And those leaves would be an excellent source.

But before we get to that, let's back up a bit and answer the question, "How does carbon get into the soil?" Okay, the first step is that green plants pull the carbon (as CO2) from the air.

Green plants pull carbon from the air during photosynthesis.


I know you probably studied photosynthesis in school, but let's do a quick review...

Green plants combine carbon dioxide from the air and water with energy from the sun to form sugar or glucose which can then combine to form starches and fats or whatever the plant needs.

Plants store carbon in their wood, roots, leaves, flowers and fruit. 


Then the vast majority* of living organisms (plants, animals, fungi, bacteria) digest the sugars that the plants made in one form or another to gain energy for life through respiration, a process the equal and opposite of photosynthesis. This happens on a cellular level. When we breathe out that’s just the final stages of our metabolizing process. If you’re a fan of Star Trek, Spock, the science officer, would describe us and almost all earth's organisms as carbon-based life-forms.

This black swallowtail butterfly larva was in my parsley a few years back. They use members of the carrot family as their larval food source. As it consumes the parsley to gain energy for life, the carbon is transferred from the plant into its body and cycled through its systems. Some carbon is released during its respiration, some is released as waste, and some carbon is stored within its tissues while it's alive, but it’s all released when it dies and decomposition sets in. Decomposition organisms transfer the carbon to their bodies and then as they respire, it's released as carbon dioxide.

Words of advice on sequestering carbon into our soils from "Climate of Hope"
by Michael Bloomberg and Carl Pope. 

How is carbon transferred to and stored in soil?

When your soil is healthy, it supports a whole
ecosystem from microbes to insect eaters
such as this lovely toad.
In a natural environment, trees, shrubs, and herbaceous plants shed branches, twigs, and leaves as they live and die. Animals living in the forest shed their skins, deposit their waste, and eventually their whole bodies on top of or under the soil. This creates a duff layer, which acts as a natural mulch. And then the soil organisms including, bacteria, fungi, nematodes, earthworms, ants, salamanders, toads, insect larvae, moles, and more, all make their living in one way or another from the carbon-based materials that natural debris and in the process turn it into humus and as it's broken down with each step, it eventually yields nutrients for plants. In a balanced soil ecosystem the cycling of nutrients is mostly closed, which means that the rate of decomposition and nutrient release is very closely matched by the rate of uptake by plants. This means that the carbon stored in the soil remains stable.

But our yards are NOT natural ecosystems. 

Typical urban and suburban yards have been mowed, trimmed, raked, and generally cleared of organic materials that would have become part of the soil. And in many cases, homeowners and other landscape managers purchase mulch to cover their bare soil to keep down the weeds and keep in the moisture. Often it is unsustainable bagged cypress mulch, which used to be made from waste from saw mills, but now whole forests are being shredded to feed our mulching habit.
Cypress mulch is the least sustainable choice. 
But there are more sustainable ways to manage landscapes that will keep or sequester carbon in the soil.

- Reduce raking, trimming, and clearing by leaving more wild spaces in the landscape and allowing nature's mulch to accumulate.
- Retain the natural mulch. For areas where raking and clearing is done, save that natural material to build compost piles or to add as mulch to uncleared areas. This might also include using the yard waste collected by your neighbors. (I have a neighbor who has a lot of pine trees in his yard and when he rakes up those pines needles from his lawn, he loads them into his yard trailer and brings them to our yard and adds them to our pine needle pile.)
- Use sustainable materials for added mulch. Ask for the chipped wood from tree cutters, rake up pine needles from the streets, or purchase mulch made from invasive trees that have been removed from natural areas.

Ask for tree cutters' loads to use in your yard. So next time you see this, bring it home.
There is a whole section on soil
in our award-winning book,
"Climate-Wise Landscaping:
Practical Actions for a Sustainable Future
Over 15 years, we've added more than 20 loads of tree cutters' woodchips to our landscape. Just think of all that carbon that has been recycled and absorbed into our local ecosystem.

- For more details on soil as a working ecosystem, read my post on soil for the Gardening Know How blog: Soil: We need to stop treating it like dirt!
- For more information on mulch and mulching errors read this post: Mulch is NOT the point of a no-lawn landscape.
- For details on why you shouldn't use peat moss: (Peat moss is never sustainable)
- For more articles on composting and mulching, see my Green Resources Page on this blog.
- For extreme details on soil, read the Soil Section in "Climate-Wise Landscaping."

This fall and winter I hope you find more ways to sequester more carbon in your yard.

Green Gardening Matters,
Ginny Stibolt

* So as I mentioned, ALMOST all of life on the planet depends upon photosynthesis today, but one group that does not are microbes that sustain themselves at deep-sea hydrothermal vents that are rich in hydrogen sulfide and other compounds. Those microbes are at the base of an ecosystem that includes larger organisms such as worms, crabs, and more. All of this happens in total darkness. See this Smithsonian video.


  1. I am hesitant to pick up bags of leaves where I am not sure whether the yard has used those TruGreen, etc. chemicals. Should I get over this, especially where I am using the leaves and detritus only for mulch on non-edible plants? (And should I, in fact, use caution about what leaves go in to my compost pile/use as mulch on my veg beds?) Thanks!

  2. Hi Jessie,
    I understand your concern, but most lawn maintenance people apply their poisons and synthetic fertilizers on raked or cleared lawns. So the leaves raked from these poisoned lawns are unlikely to have a significant chemical residue and if you compost them, the composting microbes will break down these poisons. So by the time you apply the compost to your landscape, it should be safe, even for your edible beds.