How Do Purple Flags Fight Climate Change?

Last month’s article described how the restorative gardening team at the GFE is changing the way we manage our orchard. We were motivated by a massive attack of weedy Oxalis pes-caprae in the orchard floor. So we decided to stabilize the sandy steep hillside of our orchard with “urbanite” retaining walls and to plant mixed perennials (marked by purple flags) in the orchard floor. These steps should allow us to outcompete the oxalis with desirable plants and to provide better access for maintenance. The urbanite will also adjust the pH of the hillside soil to benefit the fruit trees and discourage the oxalis.

That story alone demonstrates many of the basic principles of organic gardening, because we worked over time to change the conditions that favored the weeds without using any synthetic pesticides. We had to understand our site in detail including the slope, soil type, soil chemistry, the weed’s life-cycle, and interaction with surrounding plants as well as our own habits and how our maintenance was fitting in with the site. So far, so good. But there is another aspect of the project which lifts it from the traditional views of organic gardening and puts it into another category: restorative gardening.

In part of last month’s story we mulched the orchard floor with sticks sifted out of the compost pile. We were trying to smother the growth of the oxalis while enriching the sandy soil. This is an example of the traditional view of organic gardening. Here, gardeners create a living soil by adding organic (carbon-based) matter to the soil either as compost, mulch, or green manures. We organic gardeners primarily focused on the decomposition of these materials in the soil as a way to feed the soil and keep the soil microbiome alive. Soils high in carbon are high in life forms, soils high in life are high in carbon. It works both ways.

Organic matter mixed with soil creates a healthy ecosystem for beneficial microorganisms.

What we are learning now is that the presence of green growing plants is even more important to building a living soil than the presence of decomposing organic matter. By planting a mixed perennial meadow under our fruit trees instead of constantly disturbing the soil with weeding, we are adding much more carbon to our soil over time than we could by simply mulching.

While getting rid of the oxalis weeds is great, getting rid of the carbon dioxide that is driving climate change is much more important.

Here’s how the purple flags which are helping us establish a green orchard floor are also helping us impact climate change. (User alert: this article is now going to get technical and dense. If you don’t have the bandwidth right now, skip to the end.) 

The soil microorganisms that keep the soil alive get their energy from “solar power” – photosynthesis that has been done above ground by green plants. We already know that green plants use the sun’s energy to feed pollinators with a tiny drip of sugars in their nectar. Now we are finding that they also are feeding the life under the soil by constant, tiny exudations of sugars, gums, waxes, and other vital compounds from their roots.

These underground life forms include many different fungi and bacteria which form great underground webs in the soil. Although they have no access to sugars made from photosynthesis on their own, they can get this energy from plant roots. Then they feed the plant in turn in a symbiotic relationship. They spread much further in the soil than the plants roots can, so they can access distant water and minerals and bring these to the plant roots in a sort of biological barter system that benefits both.

Fungi webs stretching through a block of soil.

Here comes the exciting part. At the very beginning of this process, green growing plants scrub carbon dioxide (a greenhouse gas) out of the air, turn it into sugars, while exhaling oxygen. So they are fighting climate change by photosynthesizing. They build this energy into their own bodies, and also feed animals (including us), and feed the soil microbiome. Carbon that used to be a problem in the air becomes a solution in the body of a green plant. What happens to the carbon next?

Part of this carbon ends up in decomposing plant material or is eaten by animals and turned into manure. Composts and manures spread on the soil, or dug into the upper inches of the garden, or leaf litter dragged down by earthworms and excreted as castings all add to the carbon content of the soil. Decomposing plant material, dug by organic gardeners into the top inches of the soil sequesters carbon that used to be in the air. But the next time this soil is dug up, much of that carbon escapes back into the atmosphere again. On a large scale, when traveling through farmland, you often see bare, tilled soil which has been dug or plowed between crops, to create a “clean” farm, garden, orchard, or vineyard floor. These agricultural techniques allow carbon to be released back into the atmosphere. Tilling, along with synthetic fertilizers, has led us to reduced soil carbon levels and poor soil structure in agricultural land.

The same is true on a small scale for backyard gardeners. When we expose and turn over soil for a new planting, we are allowing the carbon from our last batch of manure or compost to leak back out into the atmosphere. This doesn’t mean we should never dig in our gardens, but it does mean that most of the garden should be planted with a stable and permanent plant community that can offer continuous support to the underground webs of soil microorganisms. At GFE this is the mixed “border” of summer-dry and native plants and perennial food crops that surrounds the raised beds for annual vegetable production.

Because where soil is continuously covered with green plants, the carbon from the atmosphere can go to feed stable webs of underground microbial life. This carbon will end up deep in the soil. Living microbial webs will extend in the soil at least as deeply as the plant roots penetrate. This can be several meters deep in the case of trees, and there are many other deeply rooted plants like many of our native perennials and shrubs and tap-rooted annuals like borage or California poppy. As a result, carbon which used to be in the atmosphere is deposited deep underground in the living webs of microbial life, and it can stay sequestered in the soil for very long periods of time.

By some estimates, using agricultural techniques, which avoid plowing and build permanent plant communities, could double soil carbon contents in as little as ten years, and remove most of the excess carbon dioxide in the atmosphere which is driving climate change. This is crazy hopeful and absolutely dizzying to anyone who has fallen into pessimism about the future of our planet.

Please don’t believe me, read about it in the original sources:

• “Grass, Soil, Hope” by Courtney White gives an exciting and accessible read.

• “The Carbon Farming Solution” by Eric Toensmeier includes a very technical analysis of the carbon sequestration potential of perennial cropping.

• Any of the work of Dr. Christine Jones is hopeful and inspiring.

Locally this view is being put into action at Paicines Ranch by Sallie Calhoun and the No Regrets Initiative as well as Straus Family Creamery and many others. Learn more of the international viewpoint by finding out about the 4 for 1000 Initiative in France (Quatre pour Mille).

The understory meadow is gradually taking over the south orchard at GFE.

By changing our vision for our orchard floor from a weed-free, mulched understory to a thriving green mixed meadow, we are beginning to demonstrate at GFE a new vision for environmental gardening. We’re going beyond the idea that we should not pollute by our gardening practices by using synthetic chemicals and fertilizers. We are going beyond conserving resources by not overusing water, and by not producing trash. We are entering a new ethic for a new millennium called restorative gardening and farming, which builds soil carbon.

This is where gardeners, city planners, farmers and ranchers, can and must fight climate change. We can create a more resilient and biodiverse world by choosing restorative solutions when we are entrusted with land, however small.