Biochar in my garden

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An Introduction to Biochar

Additional excitement came with the discovery of deep dark areas of “terra preta do indio” — Indian black earth — in the Amazon rainforest where the soil generally is thin, red, acidic and infertile. The patches of terra preta are alkaline with a high carbon content, and contain pot­shards indicating that it was not natural: a pre-Columbian civilization had created it. It is extracted and widely used by garden contractors because it is so fertile. It has remained fertile and retained its carbon content through the centuries.

Terra preta is black because it contains large amounts of charcoal. Infertile land had been converted to fertile land that supported a thriving civilization through the wise use of the trees that had been felled. Could charcoal, therefore, not only be a vehicle for reducing global warming but also a means to increase the fertility of degraded land, and help feed the world?

Charcoal used for this purpose is referred to as biochar. Biochar is pulverised charcoal made from any organic material (not just wood) and, when mixed with soil, it enhances its fertility. It locks carbon into the soil and increases the yield of crops. To many, this appears the closest thing to a miracle.

I have added biochar to my garden along with compost and am amazed at the positive impact it has had on my soil and crops. How to make Biochar?

To make biochar, pile up woody debris in a shallow pit in a garden bed. Burn the brush until the smoke tins and then damp-down the fire by covering it with about an inch of soil. Let it smolder until the brush is charred, then put the fire out.

Unlike tiny tidbits of ash, coarse lumps of charcoal are full of crevices and holes, which help them serve as life rafts to soil microorganisms. The carbon compounds in charcoal form loose chemical bonds with soluble plant nutrients so they are not as readily washed away by rain and irrigation. Biochar alone added to poor soil has little benefit to plants, but when used in combination with compost and organic fertilizers, it can dramatically improve plant growth while helping retain nutrients in the soil.

Try it. Just don't stand in the smoke like I did. You'll be smelling like an open fire for two days!