Mar 3, 2013

How to make biochar | Living the Country Life

Convert plant and animal waste into a fine-grained, porous charcoal that helps soils retain nutrients and water.
By Mitch Kezar

Cathy Rose makes homemade biochar on her small farm near Delano, Minnesota

Cathy Rose rolls a rusty old steel drum from a storage shed onto the gravel driveway, scraping a flat spot for it with her boot. She goes back for a second and then a third barrel of different diameters, hiking them by knee one atop the other like a Dr. Seuss crazy hat. The contraption isn’t an artsy farm burn barrel, even though that’s pretty much what it is. Cathy is making homemade biochar at her Nature’s Nest Farm west of Delano, Minnesota. This ancient form of fertilizer is gaining ground as a new tool for growing things well.

How it works

To make biochar, says Cathy, you can use any kind of plant matter – tree limbs, twigs, clippings – plus manure, bedding, whatever. Load up the bottom barrel with loosely packed biomass and light it. The three barrels work to create a rocket stove chimney that is the most efficient way to cook.

“The extremely hot fire cooks the biomass down fast, and fast is all about making combustion without making much carbon,” says Cathy. “It’s a scientifically proven way to burn.”

The second barrel rides about 18 inches over the top of a 55-gallon drum. The top barrel is smaller in diameter, which creates the chimney, pulling air through the fire from the bottom. Cathy punched big holes in the bottom of the lowest barrel to get that draft in the chimney working.

She burns it for about an hour or so, and then she snuffs out the fire by closing off the airflow. “I can choke off the fire either with water or by starving it for air – anything so it doesn’t burn all the way to ash,” she says. The biochar produced from her bottom barrel yields about a half bushel.

“From this half bushel, I can treat a good-size garden,” says Cathy. “Unlike lump or processed charcoal, this granule stuff gleans and glistens, and it sounds like broken glass when it dries.

“The biochar I’m making is burned down to small particles, so even the dust is important. A little of this stuff goes a long way,” she says. The hard part is getting it spread evenly. The tiny particles are full of air, the opposite of clay.

“It’s amazing how these particles go about doing their work, like dust, and they still have the capacity to enhance the soil and to carry nutrients,” she says. “I’m never able to spread it as thinly as I need to in order to get its full benefits.

Start small

She used to buy biochar and mix it into her garden. “Now I make it myself,” says Cathy. She encourages new gardeners to use it first in a small plot to understand how it works.

“After you see what it does, you can begin to use it on a larger scale,” she says. “It increases your production with such a little amount of effort and energy, you’ll be amazed!”

The process works on any scale. Cathy knows a farmer who burns manure from 80,000 chickens. He has a computer-operated burner and uses the captured heat to power and heat all his farm buildings. He then sells the biochar produced.

Mix with compost

Homemade biochar needs to be charged with nutrients before being added to the garden. You can mix it with compost or soak it with worm castings tea or a nutrient-rich solution like urine or fish emulsion.

Cathy applies the final product in a thin layer close to the plants. You can also top-dress the soil and work it in with a tiller to the first 4 to 6 inches.

“The longer it’s in the soil, the more the pores fill with microbial activity feeding the soil again and again,” says Cathy. “You use it in a perennial garden or around your trees. If that tree was standing in clay soil, you just made holy ground!”

What Is biochar?

According to the International Biochar Initiative (, biochar production is a 2,000-year-old practice that converts agricultural waste into a soil enhancer that can hold carbon, boost food security, and discourage deforestation. The process creates a fine-grained, highly porous charcoal that helps soils retain nutrients and water.

Biochar is found in soils around the world as a result of vegetation fires and historic soil-management practices. Intensive study of biochar-rich dark earths in the Amazon (terra preta) has led to a wider appreciation of biochar’s unique properties as a soil enhancer.

Pre-Columbian Amazonians are believed to have used biochar to enhance soil productivity. Their method worked by smoldering agricultural waste in pits or trenches. They would cover burning plant matter with soil.

Biochar can be an important tool to increase food security and cropland diversity in areas with severely depleted soils, scarce organic resources, and inadequate water and chemical fertilizer supplies.

Biochar also improves water quality and quantity by increasing soil retention of nutrients and agrochemicals for plant and crop utilization. More nutrients stay in the soil instead of leaching into groundwater.

How to make biochar | Living the Country Life

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