Wood stove biochar experiment
I started damping our Jotul
F 602 wood stove
down at night, I realized that the stove makes copious amounts of first
class charcoal. Thirteen days of fires filled up our bucket
beyond the brim --- time to figure out how to filter the charcoal from
Both wood ashes and
charcoal are good for the garden, but they have different uses.
Ash is high in potassium, and also contains quite a bit of phosphorus,
magnesium, and various trace minerals. More important, though,
wood ashes are a quarter to a half calcium carbonate (aka "lime"), so
you have to be aware that you will raise the pH of your soil by
applying the ashes. Since our soil already has a pH around 6 and
our potassium levels are naturally very high, I don't want to apply too
much ash or I'll raise the pH above the optimal 6.5 recommended for a
vegetable garden and possibly bring the potassium up to toxic levels.
The charcoal is what I'm
really excited about. We've been sold on the benefits of
biochar to soil,
been ready to put in the time to build a biochar production
chamber. Sure is nice of the airtight wood stove to do that job
for us while also producing plenty of heat to keep my toes warm.
I built a sifting box to
separate the charcoal from the ashes, a process that went pretty
smoothly but needs a bit of tweaking. First of all, even though
the coals had been sitting in the ash bucket for nearly twelve hours,
some were still burning, and I scorched the wood on
the inside of my sifter. Mark suggested adding flashing to the
inside, which is a great idea. The job was also pretty messy, with ash flying everywhere --- maybe I need to add a lid to the top of the sifter?
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Despite needing some
optimizing, the sifting operation went quickly once I realized I should
only dump in about four inches of stove debris at a time and jiggle the
sifter a lot to get the ashes to fall through the holes. The
really difficult bit will be figuring out how to crush the biochar into
powder. We could use the chunks as they are, but my understanding
is that we get more surface area and more microbial action if we crush
the biochar into much smaller pieces. While we put our thinking
caps on, I'll be storing our charcoal in a metal container so that it
can't burn through the bottom and start a fire.