Part one of a series about using regenerative gardening techniques to enhance carbon storage while improving soil health.

To make it simple as a crayon sketch, there are two ways to mitigate climate change that, in tandem, could work. One is to lower emissions. To decarbonize, if you will—and de-nitrous oxide-ize, de-methane-ize, and de-soot-ize as well. It is true that to keep the earth’s average temperature from warming more than 2° C (3.6° F), emissions will have to fall. Drastically. Which means lifestyles, in fact whole cultures and economies, will have to change, and everyone, especially the well off, will have to share in the sacrifices and changes to be made. This necessity is the real inconvenient truth implied by the inconvenient truth of climate change and one mostly being ignored or rationalized away by pretty much everyone, except a small percentage of realists. Part of the problem, I think, might not be so much willful ignorance as a failure of imagination. Quite a few people I speak with about climate change—well educated, thoughtful, caring individuals for the most part—simply cannot imagine what it would be like to live even a slightly less oil dependent version of the life they currently live, though they grasp the facts and urgently agree that something must be done.

As for the second, carbon sequestration, or pulling carbon out of the air and storing it deep in the ground, as noted environmental journalist Elizabeth Kolbert points out in a recent article, no one knows how to do this.

So far, technology-based carbon capture and sequestration hasn’t panned out

However, this is not precisely true, though in a modern technological sense of course it is. Anyone who owns or rents a little land on which plants grow can, him or herself, sequester carbon, and may even be doing so at this very moment without even realizing it. It’s not hard. Healthy soil does this naturally. All we have to do is help nature along. And as we do so, we can help improve ecosystems, improve soil fertility, and even help endangered species survive. Regenerative farmers and ranchers are doing this in a big way all over the world, though the ones I’m most familiar with are working in the US, in places like North Dakota, Illinois and Minnesota. Even though farming and gardening practice has usually, seemingly inevitably, depleted the soil, scientists such as R. Lal, Christine Jones, Nicole Wander, Michel Cavigelli and others, as well as entities such as the Rodale Institute, have shown that regenerative techniques actually rejuvenate the soil and sequester carbon. And, not only is their, and others’, long-term research showing how and why this works, but scientists are also teaming up with farmers to demonstrate and study practical techniques—and even conducting classes to teach farmers soil conservation methods. This is vitally important work, since agriculture and other domestic land management is responsible for something like 30% of greenhouse gas emissions worldwide.

But what about the rest of us? 
My yard is much smaller than the typical ¼ acre suburban plot; my garden encompasses about 2,000 square feet, smaller than many houses. Most people in the US and elsewhere live in similar urbanized areas. Large-scale carbon sequestration on vast acreage, as potentially could be practiced by farmers (some two percent of the US population) is beyond reach. We regular folks are left with yet another situation where direct-action participation in solutions to the climate disruption problem might seem impossible. Most of us aren’t off-grid homesteaders; we rely on the local utilities and pubic services; non-existent public transit might force us to drive even if we’d rather not; and other realities of our everyday lives might prevent us from doing as much as we’d like. Even if we can imagine what is necessary to be done, and are prepared to help decarbonize our society, we might feel powerless, possibly unable to take positive, rewarding action to help remedy the situation.

Yet we can do something. Quite a lot, actually. For the first part, we can consciously reduce our lifestyles and become actively civically engaged; for the second, we can practice backyard carbon sequestration by becoming carbon gardeners, ourselves, and in the company of others. I agree with those that argue that unless there are mass movements and unless governments and corporations change their ways, individual changes won’t mean that much. However, I also believe that the butterfly effect is just as real in human systems as in earth systems, and in fact, backyard soil carbon storage works in both at once.

Thus I say, again, strongly, to everyone who is in charge of caring for a backyard, front yard, side yard, or some other patch of ground where plants grow, soil carbon sequestration is something you can do, on your own, fairly easily. You will have to give some things up, such as synthetic fertilizer, but rather than feeling deprived, you will be helping create abundance.

We can help nature do the job

Considering that we in the US have in excess of 40 million acres of lawn and untold millions of acres of conventionally cared for gardens (including “landscaping” and vegetable gardens), there’s room for a great deal of carbon sequestration on domestic and institutional land within cities, suburbs, towns, villages and hamlets. In 2005, Christina Milesi and others built a computer model that calculated how lawn with moderate fertilizer and an inch of water a week does indeed sequester more carbon than it releases, particularly if grass clippings are left on the lawn when it is mowed. (She also demonstrated that in large swathes of the country, without coddling, lawns would basically cease to exist.) I’m not sure anyone has ever calculated the potential sequestration that could be achieved through consciously regenerative practice on so huge an acreage. If someone reading this can do so, please let me know. I would love also to see field experiments in backyards, of the sort carried out on ranches and farms, which would assess different kinds of urban and suburban gardening practices for carbon storage.

Now when it comes to deep carbon storage, anyone practicing various forms of ecological gardening, organic gardening, permaculture or bio-dynamic gardening is already at least part way there: carbon sequestration is part of everyday practice. However, in the US at least, as with regenerative farmers, permaculturalists and other gardeners of their ilk are few and far between. Even if you add the daily growing host of wildlife, native plant, and pollinator gardeners, the needed acreage is not increasing quickly enough. And because most of these folks are not explicitly gardening for carbon sequestration, there are still things they can learn. Though for many, all that’s required, perhaps, is some new information, a shift in perspective.

What every would-be carbon sequestration DIYer needs to know 
Compost doesn’t store carbon. Like other ecological gardeners, I know that having a healthy soil biome is very important in all kinds of ways. I’ve always made compost and added it to my beds, and also use it to top dress my polyculture lawn. It’s vitally important because it helps plants grow better, without the need to add synthetic, inorganic fertilizer. I’ve also known that it’s important to provide lots of organic matter because the soil critters—the fungi, bacteria, arthropods, nematodes and so on, utilize that organic matter and in turn, convert it into nutrients plants can use. In just one example, most gardeners know that the nitrogen-fixing bacteria that colonize the roots of legumes such as clover can convert nitrogen from the air into a form plants can use (one reason it’s good to grow clover in your lawn). However, healthy soil also contains free-living soil bacteria and other microbes that do the same thing. In my yard, more organic material gets added in the form of grass clippings left in place, and fallen leaves left under bushes and trees to develop naturally into duff. Organic mulch is also helpful, in terms of protecting the soil and helping provide nourishment to the soil critters. I can confidently say that my soil has plenty of organic material, especially in the areas that are planted with native prairie plants: they are deep rooted, and approximately 1/3 of the roots die every year, providing even more organic matter for all these critters to live on.

So far so good. However, what we are after is deep, stable carbon. And that is not provided by the process of breaking down of plant residues, manure and the like into compost or incorporating organic material into the soil. Strictly speaking, that catabolic process releases CO2 into the air as the decomposers and other critters access nutrients. What is needed is the creation of humus: we want to foster the relationships between actively growing plants, fungi and soil microbes and all the other critters that build soil. It is humification that, as topsoil is built, stores carbon at a deep level and in a stable form that can stay in storage for hundreds of years, as long as it is part of a healthy ecosystem or good soil nurturing methods are used.

Humification stores carbon and depends on actively growing plants. How does this work? Very briefly, here is what happens. While plants are growing, they pull carbon dioxide out of the air (and absorb water through leaves and roots). During the complex process of photosynthesis the CO2 breaks down into oxygen, which the plant releases into the air, and carbon, which gets combined with water and converted into the carbon sugars the plant uses to fuel itself. However, something else happens to the carbon sugars, which might, intuitively, seem counterproductive. Some of this “liquid carbon,” as Australian soil scientist Christine Jones calls it, travels down to the roots, and, as it fuels their growth, a portion leaks out of the roots into the soil. Why would this be? It would seem inefficient, like the leaky faucet in someone’s bathroom that wastes water and increases the owner’s monthly bill.

The answer is that, like canny traders, plants use the liquid carbon, or “root exudates,” as a kind of exchange medium, which they trade to mycorrhizal fungi, bacteria and other microbes not only in return for nutrients such as nitrogen (those free-living bacteria get their own carbon fuel by living in association with growing plants) and phosphorus, but also the wide range of other nutrients plants need to help fuel growth. In fact, in healthy soil plants get 85-90% of nutrients they need through this carbon exchange. In the process, vast networks of mycorrhizae form in the soil, connecting plant roots with nutrients they couldn’t otherwise access. Unlike with the water waste and higher bill, plants don’t seem negatively affected by this loss of carbon sugars. Rather, the more mycorrhizae and microbes there are getting fed, the healthier the soil and the healthier the plants.

What happens to the carbon sugars: how does the humus build? 
The story doesn’t end there. The mycorrhizae themselves, having utilized the carbon sugars and supplied plants with nutrients, also practice exudation: in this case a gluey, sticky protein called glomalin. With other gums and glues produced in the carbon-nutrient exchange, glomalin aids in the formation of soil aggregates by sticking together particles of sand, clay and silt into the larger clumps that that collectively we call humus, which is where the real carbon storage action is. Glomalin is thirty to forty percent carbon and is incredibly stable and long-lasting. Soil high in humus is soil that is storing carbon—humus is about 60% carbon. It’s only since 1996, when Dr. Sara Wright described glomalin and its role in humus production, that we have been able to accurately measure the carbon being sequestered in soils, so we now can assess our carbon-storage efforts. As important as carbon storage, however, is the effect soil aggregation has on nitrogen: the aggregates that form humus also enable nitrogen-fixing bacteria to function, enabling plants to get more of the nourishment they need

As long as there have been gardeners, humus has been appreciated, since its presence happens to guarantee that soil is fertile and has good tilth—it has plenty of texture: porous, “fluffy,” with air pockets, room for water penetration and good water holding capacity, among other virtues. Soil in good tilth often looks a little like “black cottage cheese,” as farmer Gabe Brown has described it: it doesn’t pour through your hands like sand or break into large, hard chunks like clay. Humus isn’t something you can separate out of the soil. Structurally it is the soil, woven throughout the way novelist Henry James once described meaning and symbolism being woven into a novel like the design in a carpet. As every good gardener knows, humus-rich loam is the best medium for growing flowers or vegetables. What is new is the discovery of the relationships that build humus and how all that carbon gets stored—and also what disturbs the system.

Barriers to carbon storage 

1% Carbon on left; 5% Carbon on right

It’s clear that no matter what, building soil health would be very desirable, but that carbon storage makes it essential. The key is to help soil store more carbon than is released, while at the same time encouraging nitrogen fixation and general nutrient production. Unfortunately, a number of standard farming and gardening practices prevent these desirable processes. For example, applying synthetic NPK fertilizer shuts down soil production of nitrogen and slows down or even halts humus formation and carbon storage. Aspects of these processes are being demonstrated in numerous long-term studies, such as the Morrow plots in Illinois and the Beltsville Farming Project in Maryland. Christine Jones says that when they are fed NPK fertilizer, plants cease to produce the liquid carbon, and the soil begins to deteriorate due to the broken relationships. Also, plowing, tilling or extensive digging slices up soil aggregates, breaks up the vast fungal networks and, by exposing the soil to air, releases CO2 and nitrous oxide. Soil structure declines, and so does its biological health. And finally, leaving soil bare for months at a time means depriving the soil biome of the benefits that growing plants provide by interrupting vital relationships and starving the soil critters. These three practices can result in compacted, poorly textured, soil that is infertile, and unable to manage water or grow plants.

Carbon sequestration happening here

We can all be carbon gardeners
So, what to do? How can we actively foster all the biological relationships that build up the carbon reserves in our gardens and by so doing, building resilience into the soil system, thereby helping build resiliency into earth systems and our human society? In part two, I’ll discuss practical methods for turning a backyard into a carbon sink.

Online Resources:

CO2 cloud image via shutterstock. Reproduced at with permission.