Yesterday evening my son and I did an experiment with making biochar in a cone-shaped pit.

Bruce from Red Gardens on YouTube has a good video in which he uses this process:

This method appeals to me because it costs nothing and does not require burning fuel to make the biochar. The whole “barrel inside a barrel” method always struck me as wasteful and quite potentially retarded. I much prefer lower-tech solutions.

One of these, the popular Kon Tiki biochar kiln, is low-tech but seems well-designed, as well as being a step up from burning right in the ground:

If someone gifted me one I would not complain, but I also won’t bother buying or building one, as burning in a pit works quite well, as even the creators of the Kon Tiki biochar kiln note in an article posted at the Biochar Journal:

“Inspired by Josiah Hunt, we tested the production of biochar in an open earth kiln. And it worked just great. In the first attempt, we made a few hundred liters of excellent looking biochar in a conically excavated hole in the ground. This success was reason enough to construct a more precise theory about the system and to consider how it could be implemented with better technology and control.”

Since my soil here is wretched, I am going to test biochar on a bed to see if I can increase soil fertility and the ground’s ability to hold on to nutrients.

How We Made Simple Biochar

We dug a small conical pit in an old sand pile for our first burn, then gathered sticks from the woods and broke them up into manageable sizes. We started with a small fire in the bottom of the hole, let it burn down to nice coals, then loaded another layer on top. We repeated this five times with progressively larger layers as the pit’s diameter increased. When the last layer had turned into coals, my son sprayed the fire with the hose until it stopped hissing and glowing, which took a remarkable amount of time.

This morning we went out to check on our char, as it was dark last night when we finished. To our satisfaction, we had a good quantity of nice, black, fully pyrolized material.

Our little test was quite successful, yielding about seven gallons of char:

The biochar is black, well-burned and finished nicely with only a couple larger unburned pieces from the last layer, which we removed and will add to the next burn.

This is my type of method. All we needed was a shovel and a lighter, plus a hose to extinguish the burn.

Why Biochar?

I don’t like the way the gardens are doing right now and want to use every trick in the book to improve them.

After gardening in the volcanic soils of Grenada, this is like gardening on a parking lot. It’s going to need some serious help.

I’m going to set up some beds for testing different methods and see what happens. We’ll try biochar in one, nothing in another, no-till in a third, Steve’s fertilizer mix in a fourth… it’ll be interesting.

After Steven Edholm’s reports on the efficacy of biochar for increasing fertility in poor soil, I am finally ready to give it a good test. I’ll probably dig a larger pit, though. This little pit took about 1.5 hours to make seven gallons of char, but if I had given it another layer of wood at the end its maximum yield would likely end up at 10-12 gallons. If we make a bigger pit we could likely get 25-40 gallons per burn.

Then I’ll have lots of char to test in the gardens. The trials will commence shortly.

I can’t put in the biochar yet as it hasn’t been “charged.” But that’s a post for another day.