Storey Publishing, LLC, January 2018, 128 pages, $12.76
Book Review by Jessie Haas
Can your garden, brush pile, and wood stove save the planet? Yes, according to Jeff Cox, in his new book, Gardening with Biochar. Cox, a contributing editor at Horticulture, brings his scientific chops to this short book. Four chapters cover the history and science, how to make biochar, how to inoculate it, and how to use it in your garden.
Why would you want to?
Biochar can boost garden productivity, improve tilth, and buffer the effects of heavy metals. But the big reason to use it is that it sequesters carbon. “Scientists estimate that if we could increase the amount of carbon stored in the world’s soils by just four parts per thousand each year, we could sequester 100 percent of the carbon we currently add to the atmosphere annually,” Cox says.
Biochar is a charcoal, roasted (not burned) at 660°F. It can be made of any organic material, but woody plants are ideal. Plants spend their lifetimes drawing in and storing carbon. Much of that carbon is released when the plant dies. But converting it to biochar and incorporating it into soil retains most of the carbon, for centuries.
Biochar was invented by early peoples in the Amazon Basin. The soil there rapidly hardens after trees are cut, becoming incapable of suppporting crops. But 2500 years ago, indigenous people discovered that incorporating biochar and organic material made the soil extremely fertile. Over a region as large as France, they established dense populations and large cities, on soils that are still fertile today.
Cox covers this history, and the science of biochar, in the first forty pages of his book. Then he tells us how to make it, covering feedstock (including the pH impact of different kinds of wood). He recommends accumulating and drying woody debris in the spring and summer, chipping it and storing in loosely covered barrels. Come fall, you can make a burn pit (the most productive method), a TLUD (Top-Lit-Up-Draft gasifier), which is the cleanest method, or save your feedstock until winter, when you can roast it in a sealed metal container such as an ammo can in your woodstove, while simultaneously heating your house. For each method, Cox provides clear instructions and photos. He also gives guidance on buying biochar at the garden center.
Once you have your biochar, you need to innoculate it. It naturally repels water, and when powdered can easily blow away. But mixing a minimal amount of water, along with compost, manure, ‘worm juice’ or even flour, like making a sourdough starter, gives microorganisms a chance to colonize the many nooks and crannies. Without this step, biochar will lie inert in the soil for a season or two and may even retard crop growth initially.
Once your char is innoculated, it’s time to add it to the garden. Cox lays out a couple of methods, but this is a less-detailed section of the book—because really, it’s pretty simple to use biochar once you’ve prepared it right.
“Every bit of biochar makes a difference,” Cox says. “The more biochar makers we have on this planet, the more we can reduce the effects of global warming. Each year, terrestrial plants absorb 60.6 billion tons of carbon during photosynthesis. About the same amount cycles back into the atmosphere through plant respiration and decomposition.” But about 10% of that carbon is defined as waste; straw and cornstalks, wood trimmings, branches, leaves, and brush. If all of that six billion tons were made into biochar, that would offset most of the carbon dioxide humans release every year. That’s more than you can do in your garden, but every little bit really does help.