To the right of my porch is a small path that curves down the hill to a gate made from curved cedar, the type of trees that grow in the lower canopy of our Washington forests and wind their way towards the filtered light. Inside the gate are beds that resemble what most of us think of as a typical market garden - rows of beets, lettuce, and other vegetables you’d expect to find at a northwest farmers market. But that’s where the resemblance ends.

If you were able to look within the soil you’d see something very different from the rows of freshly turned and tilled dirt we’ve come to expect in a garden. Instead of pulverized soil you’d see a whole network of tunnels created by roots of the plants that have grown there before, and by earthworms searching for food. Air and water circulate in these tunnels and help support billions of microorganisms that digest minerals in the soil in a process that mimics the way our intestinal flora breaks down the food we eat.

The other critical part of healthy soil is carbon. Known as the building block of life, carbon is the currency that plants offer the soil’s biological system in exchange for fertility. It is a symbiotic system as old as the forests and prairies themselves.

TILLING RELEASES CARBON DIOXIDE

When I started clearing the forest on the island to start my small farm, I did something most farmers would think ludicrous. I left many of the stumps in place. Why? I didn’t want to disrupt the mature soil system at work in the forest floor and knew I’d never till the garden beds with a tractor.

I’d learned years before from soil scientists that tillage damages our soil and makes it harder to grow nutrient-dense food, now and in the future. The practice of tilling also contributes significantly to global warming. Over the past 250 years it has released an estimated 792 billion tons of carbon dioxide into the air globally. By way of comparison, humans were responsible for just under 40 billion tons of carbon dioxide emissions in 2016, the largest annual emission of carbon in recorded history.

To understand how tillage releases carbon it’s important to remember it’s stored in all living things. Eighteen percent of our own bodies, for instance, is made of carbon. When the living tissue of plants and animals begins to decompose, carbon is released into the soil, feeding it and adding structure to the soil, which in turns allows it to store water and air.

The problem with tillage is that it introduces unnaturally large amounts of oxygen, increasing the rate at which the wood, leaves, and other organic material in the soil decompose. When carbon bonds with all that oxygen it becomes CO2, which rises into the atmosphere and contributes to global warming.

Fifteen years of tillage can lower soil carbon levels by half, according to studies out of the University of Montana. The loss of carbon influences the soil in multiple ways. Without carbon to feed the soil’s microbial ecosystem it becomes less nourishing. Carbon is also responsible for giving soil the correct texture, known as tilth. The sugars from composted organic matter pull soil particles together in what are called aggregates, creating space that allows soil to store air and water. Without this aggregation, soil becomes compacted, which makes it difficult for water and air to circulate and feed the soil’s microbial ecosystem.

The mechanical effect of tillage further damages the soil by tearing apart the biological nutrient and water distribution network, much like forcing the collapse of a city’s subway system each spring. As soil loses organic matter and carbon due to tillage, it also loses its primary means of holding water; organic matter can absorb six times its weight in water, playing a central role in preserving moisture in the soil.

Finally, organic matter and the carbon within it holds electrical properties very similar to a magnet. This electrical charge attracts nutrients and keeps them in the top soil layers. When this organic matter is broken down through tillage it’s harder for seeds and roots to access these nutrients and more likely they’ll be washed away into our aquifers, lakes, rivers, and oceans.

Mimicking nature

I first became interested in no-till gardening because of my interest in understanding natural soil ecosystems. Growing up with my family in the forests east of Spokane, Washington, I was intrigued from a young age by the abundance of vegetation that woodlands could produce.

To grow our home garden my mother weeded, watered, and fertilized. By contrast the woods surrounding our home needed no help from us to produce a tightly knit fabric of ground cover plants, bushes, and trees.

I came to learn that no-till systems operate in a manner that mimics this natural soil ecosystem. It can regenerate compacted, disturbed soils, and return carbon back into the ecosystem.

Starting your own no-till garden

So maybe you want to start your own no-till garden? All no-till strategies involve providing a layer of material that covers the ground and suppresses weeds, either by using plastic, cardboard, compost, newspaper, or the plants you grow on the bed throughout the winter, also known as cover cropping. Here's what I recommend doing:

Smother the weeds. I like to blanket my planting beds with black plastic tarps. Organic growers in Europe call this occultation, a word that means a state of being hidden from view. Using plastic may not seem very sustainable but the plastic creates a warm, moist environment in the top layer of soil. Layering it over the soil prevents young weeds from sprouting. After several weeks under your tarp, your ground will fresh, weed-free, and ready for planting.

Materials: You'll need dark colored tarps and U-shaped stakes to hold them down. I look for a UV-treated black silage tarp, 5 to 6 millimeters thick. It's easy to find in a farm store or online. 

Prep your planting bed: Before you lay down your plastic cover, place compost or composted manure on the beds and rake it into the first inch of soil. If you have plants growing in the bed, simply put the compost on top of the plants.

Spread your tarp: Lay it over as many garden beds as it will cover and drive the U-stakes through each grommet hole every four feet to hold it down. If the tarp doesn't cover the entire bed, layer another tarp over the additional space. Sometimes I cut the tarp to fit my garden beds. Make sure to leave enough to cover the edges of your pathways. 

Now it’s time to...wait: If it’s the late fall, winter, or early spring you'll need to wait six to 10 weeks before removing the plastic. If it's warm outside, say the late spring through early fall, you don’t have to leave the tarp on as long. Two to six weeks should be enough time to suffocate the weeds. Another advantage of this method: While your tarp is on the ground earthworms are moving up to the dark surface and working to break down plants and organic matter.

How to know your garden bed is ready to plant: Before removing the plastic tarp make sure your bed is almost completely clean. If you find clumps of any residual plant material, also known as organics, rake them out and put them in your compost or on the next bed that needs covering. Once you've removed the tarp, add your fertilizer, rake it in, and start what you really want to do - planting.

Kai Hoffman-Krull runs an agro-forestry market garden on Waldron Island off the coast of Washington State. For the past three years he has conducted a research project on the nutrient effects of biochar with the University of Washington and the University of Montana.

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