Woodstock Day School Biochar Intensive
Bringing Biochar to Life: A Hands-On Intensive at Woodstock Day School
June 18, 2025 | Written by Bill Hilgendorf
Last month, I offered an intro biochar course as part of the Woodstock Day School’s Intensives program. The Intensives are two days every spring where students have the opportunity to engage in hands-on, project-based learning in a subject that interests them.
One of the things I love about my job is the opportunity to talk with young people about climate change, biochar, and carbon dioxide removal. With so much anxiety about what might happen if we don’t take action, it can feel overwhelming to even know where to start.
Carbon sequestration through the process of making biochar is a simple yet scalable climate solution that anyone can learn.
The school vans arrived promptly at 9 a.m., and after a quick tour of the farm, we headed to the biochar zone and got to work. Since this was a hands-on workshop, I kept the lecturing to a minimum—but we did take a moment to review the carbon cycle, greenhouse gases, the basics of biochar, and a few words about pyrolysis and how it works.
After collecting the sticks and branches, the students got to work prepping the material—cutting it into lengths of 20 inches or less—and loading the kiln for ignition. We always begin with a top-down burn: filling the kiln with sticks up to 1 inch in diameter, then placing smaller twigs on top, along with a single piece of craft paper and some dry leaves to get it started.
Harnessing fire, of course, is one of humanity’s greatest achievements, and we all paused to watch as the flames engulfed the small material and quickly spread through the kiln. Then it was time to get back to work—splitting larger pieces, cutting long branches, and feeding the fire.
Next, we collected sticks from the surrounding area and forest floor. With 10 of us working together, we quickly gathered enough material for our demo burn in the Charcone Kon-Tiki kiln. We needed about one cubic yard of biomass to fill it over the course of the 1.5-hour burn and the dryer the materials the better the yield.
Many people don’t realize that the flames coming off the wood aren’t actually the wood burning. They’re the ignition of gases released as the material heats up—often quickly reaching over 450°C. We continued adding material to maintain the “flame cap,” which allows gases to burn off while protecting the underlying carbon from combustion.
The simple cone design of the kiln, combined with its vertical heat shield, draws cool air upward through convection. This pushes air back into the fire, reigniting any unburned gases. Because oxygen can only react with the gases above, the wood below heats in a low-oxygen environment—creating the pyrolysis conditions that convert the biomass into biochar.
For about an hour, we all worked diligently. The six students each found tasks they enjoyed, and we kept the fire going. We added the thickest material when the kiln temperature peaked at over 675°C and finished with smaller pieces.
As the flames died down, the kids took turns quenching the char with the hose—and, eventually, each other.
They then crushed the cooled char into smaller pieces using a tamper and filled buckets to take back to school. The plan was to add it to their compost. Biochar works best when it’s “charged”—when its pores and high surface area are filled with nutrients and microbiology. Co-composting with biochar, especially when the compost heats up, creates a highly active and beneficial amendment.