The Garden Decoder: What Is ‘Biochar’?

One of the perks of working for Gardenista is getting a preview of all the new gardening books on the market. Some pique our interest because they feature beautiful photography, others because they offer good advice. The reason I was compelled to pick up Gardening with Biochar? Because I had absolutely no idea what it was talking about.

What is biochar? And will it “Supercharge Your Soil with Bioactivated Charcoal: Grow Healthier Plants, Create Nutrient-Rich Soil, and Increase Your Harvest,” as its subtitle suggests?

Curious, I read through the book by Jeff Cox. A contributing editor to Horticulture and a former managing editor of Organic Gardening, he writes in the preface, “Let me just say that in my 50 years of gardening organically, my discovery of biochar and its benefits is the single most exciting and important development I’ve ever seen.”

Now are you intrigued? Here’s what I learned from the book:

What is biochar?

Above: According to press materials, Cox’s book is “the first book on making and using biochar in the home garden.” Gardening with Biochar is $12.76 on Amazon.

Biochar, a word coined by environmentalist Peter Read in 2005, refers to a type of soil amendment made of organic matter that has been cooked at temperatures above 660 degrees Fahrenheit with limited oxygen. If you slowly roast wood, brush, and yard waste in this manner, you can transform them into a kind of soil superhero. According to Cox, biochar can decrease the need for fertilizers, encourage soil biodiversity, boost water absorption in soil, loosen compacted soil, improve a plant’s ability to retain nutrients—even decrease greenhouse gas emissions!

How do you use biochar?

Above: Mixing biochar with worm castings is a great way to inoculate it. Photograph by Jim Powell, from Composting: Are You Obsessed?

You can’t simply add biochar to the soil and call it a day. You need to “inoculate” it first: “Think of biochar . . . as an enabler and preserver of soil health rather than a supplier of nutrients,” writes Cox. “When you inoculate biochar, you load it with microbial life, ready to help enrich your soil.”

How do you inoculate biochar? The easiest is to mix it with with compost (in a ratio of one part biochar to two parts compost) in a 5-gallon bucket (filled halfway with the mixture), then fill the rest of the bucket with water, stirring it every few days for about a month. Then it’s ready for use in the garden. Other methods of preparing the biochar include composting it with other compostable materials, combining it with manure, and mixing it with worm castings.

Where do you get biochar?

Above: Photograph via Pacific Biochar, one of the companies the book includes on a list of biochar retailers and manufacturers.

You can buy biochar at garden centers and stock-and-feed outlets. If you have outdoor space and don’t mind getting your hands dirty, you can also make your own biochar. Cox devotes an entire chapter to DIY biochar. The methods he details include making an open fire pit; fabricating a TLUD (top lit up-draft gasifier), which involves tools and two 55-gallon barrels; and making biochar in a metal can placed in a wood-burning stove. All of these methods involve flames up top and organic matter roasting below.

Another great resource on biochar is the International Biochar Iniatiative, a nonprofit formed, according to its website, to “provide a platform for fostering stakeholder collaboration, good industry practices, and environmental and ethical standards to support biochar systems that are safe and economically viable.”

For more on soil health, see:

• Your First Garden: What You Need to Know About Topsoil
• Dirty Secrets: 10 Ways to Improve Garden Soil
• 10 Things Nobody Tells You About Compost
• The Garden Decoder: What Does ‘Organic Gardening’ Really Mean?