Carbon + Nitrogen

Permaculture: a perfect coupling of science and tradition. Permaculture takes ancient techniques used by native people around the world and then refines them with modern science. Here, I want to talk about a scientific aspect of permaculture. Chemistry, to be specific. Let’s talk about carbon and nitrogen.


First the hot topic, carbon. Many people associate carbon with things like global warming, carbon footprints, and carbon taxes. But what is carbon, anyway?

Carbon, the 6th element on the periodic table, is the basic building block of life. In fact, one definition of organic is “carbon-based”. You find carbon in sugar, starch, oils, and proteins. Trees make their wood with carbon–about 50% carbon–and all plants need the carbon found in CO2 to perform photosynthesis.

Where else can you find carbon? Anything that’s biodegradable or plant-derived (think paper-products and cardboard) contains large amounts of carbon. Graphite (pencil led) is 100% carbon. Same with diamonds. The list goes on and on.

You are made of carbon. Carbon makes up 18.5% of your body, second only to oxygen. Life on Earth needs carbon to thrive.

Flowers in straw mulch, a good source of carbon. The straw will help retain water and–as it decomposes–add carbon to the soil.


Next, let’s consider nitrogen, a equally important chemical element. All life needs nitrogen to create DNA, chlorophyll, and protein. Nitrogen makes up 78% of the atmosphere, in the form of N2, so you breath mostly nitrogen. However, humans, animals, and plants can’t get nitrogen from the air. We need bacteria for that.

The nitrogen cycle describes how nitrogen gets from the air and into the biosphere. In short, certain plants (called nitrogen fixing plants) house beneficial bacteria in nodules on their roots. The bacteria take the nitrogen from the air and convert the nitrogen from the inorganic N2 gas to other forms, such as ammonium and nitrate, which plants can use. Thanks to the bacteria, both the nitrogen fixing plants and other vegetation can absorb the nitrogen from the soil. Animals can get nitrogen by eating the plants.

Often, soil does not have enough nitrogen. The lack of nitrogen in the the soil limits plant growth. You can add nitrogen to the soil through fertilizers, but that only fixes the problem temporarily. For a permanent solution–a permaculture solution–plant nitrogen fixing plants. Examples include beans, clover, locust trees, alfalfa, peas, and other legumes. These plants will give the soil a continuous source of nitrogen.

Give Your Garden Its Vitamins

Plants need more nutrients than carbon and nitrogen, obviously. But carbon and nitrogen are the key nutrients you need to provide. Now that you know this basic organic chemistry, how can you give your garden its “vitamins”? Consider three ways: protecting the nutrients you already have, feeding the soil, and letting nature do its thing.

Protect Nutrients

Rule #1: Never expose naked soil to the elements. Since plants take their nitrogen and many other nutrients through their roots, their roots need healthy soil to live in. However, exposing bare soil kills beneficial bacteria and washes away nutrients. Direct wind blows off the topsoil, direct rain causes erosion, and direct sunlight bakes the ground. The soil dies.

When landscaping, look for the least disruptive option. Need to remove some grass? Instead of tearing up the sod, try layering a few cardboard boxes on the patch of grass. After a few weeks, the grass with die, add its nutrients to the soil, and give you a clear patch of ground to plant in.

If you do have bare soil, cover it with mulch or a cover crop. Both will protect the soil from the elements and eventually add nutrients to the soil. Bonus points if your cover crop is a nitrogen fixing legume!

Feed the Soil

How do you add nitrogen to the soil? As one option, you can compost. The internet has countless tutorials on different forms of composting. Whichever method you choose, you’ll ultimately need 3 ingredients:

  • Carbon (from wood, cardboard, and other “brown” matter)
  • Nitrogen (from food scraps, animal manure, lawn clippings, and other “green” matter)
  • Water

Whether you compost or not, take advantages of whatever nutrients you have on site. For example, when you mow your lawn, let the grass clippings fall back to the ground, where they will decompose and release their nutrients back into the soil. Don’t throw away your nutrient-rich lawn clippings!

In hugelkultur, a method of adding carbon to the soil, you bury entire logs in the ground and plant on top of them. As the buried logs break down, they feed the plants and help the soil retain moisture.

Let Nature Be Nature

Consider a forest. No one fertilizes it, yet plants grow. They don’t just grow; they multiply and flourish. Nature knows how to take care of itself. Learn more about how nature fertilizes the soil and incorporate nature’s techniques into your own gardening.

One observation: Nature multi-tasks, using one plant for two or more purposes. You can multi-task by selecting nitrogen fixing plants that enhance your landscape. White clover mixes well with lawns. Peas add flavor to a garden. Many trees fix nitrogen as well.

Another observation: Every autumn, forests dump loads of nutrient rich leaves to the ground that eventually decompose and feed the forest floor. Follow nature’s example. Don’t throw away the leave! If you want plants to grow through the leaves, shred the leaves before reapplying them to the soil. Or, if you want to keep out some weeds, layer the unshredded leaves as a sheet mulch.

Take time to sit back, observe, and let nature teach you.

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