Carbon sequestration, or carbon storage, is the process that binds carbon atoms into harmless compounds rather than putting them into the air in the form of climate-changing carbon dioxide.

Gardeners can do this on a small scale and improve garden productivity. How we handle our organic matter will determine if our garden is sequestering carbon. Almost all of our plant materials are full of carbon, mostly in the form of carbohydrates from plant fibers. When plant materials are eaten, burned or composted, they turn into atmospheric carbon dioxide and water. Our goal is to keep the carbon in the ground for as long as possible and not let it escape into air.

One way to do this is to avoid cultivation. Exposure to air is the enemy of soil carbon. One of my fellow Master Gardeners does this and he has a most impressive garden, completely weed free. The problem with cultivation is that it exposes organic matter to oxygen and then it becomes carbon dioxide and water.

We are trying to avoid making carbon dioxide for as long as we can. Frequent cultivation is a key component of my weed control strategy, so I have to look for other practices to sequester carbon, and I found one.

Compost is very good for gardens. I dig a trench across my garden, two shovel widths wide and three shovels deep, and fill it with organic materials. The organic materials start with tree bark, small branches, and cones and needles from pine, spruce and fir trees.

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Then I add my own compost, old hay, leaves, corn stalks, squash vines and chicken manure. Nothing really needs to be chopped. The coarsest branches should be on the bottom of the trench. A manure source is really important because it jumpstarts the microbial activity and adds nitrogen fertilizer.

To finish the process, I replace the soil from the trench to on top of the compost-filled trench. You may have a mound of soil after this is done but this mound will warm up faster in the spring from sun exposure, drainage and heat from the decomposition below. This will get your plants off to a faster start in the spring.

Warm soil temperatures really help getting the garden growing in the spring. The most impressive parts of my garden are the squash, potatoes and cherry tomatoes growing on top of trenches of compost.

The best carbon sequesters are hugelkulturists, a German process of mounding or burying whole logs, tree trunks, branches, manure and compost up to four feet high or deep, covering with soil and growing garden plants on top. The organic matter breaks down over a period of many years and keeps supplying nutrients while absorbing and releasing water for the plants.

Raised bed and container gardeners can participate too. Place coarse organic matter in the bottom of the containers or beds to provide drainage. Add a layer of real garden soil. Composted manure can be added before it is finished off with raised bed soil. Use spruce and fir cones, small branches and bark for the bottom of the containers or beds. Fully saturate the bed or container before planting, this step is often left out in raised bed planting demonstrations.

Don’t expect to see a cooler climate after practicing garden carbon storage, but do expect to see some impressive plant growth. Every bit helps.

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