The nearly endless month of Farch is upon us. This winter feels like a little ice age. But hope springs eternal… Spring being the key word. With Spring planting and growing in mind, it is time to take advantage of our disadvantages. The ground around here is still protected by snow and ice. No growing is going on anytime soon. But no forest fires, lawn mowing or many other distractions are going on either. It’s a perfect time to make biochar. Biochar is just charcoal used to enhance the biology of the soil. It does not have additives to compress it into briquettes for grilling or other uses.
Northeast Washington is also a great place to make biochar. People go on about how you can make it from almost anything: poor quality firewood, dead and down trees and brush, slash piles, orchard prunings, torn down building scraps etc. I’ve used all of those things. If you have a lot of them and reducing that waste is a big objective, go for it. An advantage we have living here is lumber scraps. I that is the fuel of choice.
But first, let’s revisit the last article I wrote about making biochar in 2019, Backyard Biochar. In that article I advocated making a little oven of cement blocks or something similar because you could extract the biochar from the fire and use the left over still-flaming wood pieces to kindle another load, making it a continuous process. That was a good idea as far as it went. But although the cost was virtually nothing, it was still a lot of work for not much biochar.
Biochar has become a very familiar soil and animal feed amendment. A simple Google search for “biochar” yields 4,750,000 results in 0.65 seconds. People have caught on to the fact that biochar is good for the soil, the atmosphere and your crops. There is no need here to elaborate all the good things about it. There is plenty of information out there. Check out http://terraflora.us for a great rundown. If you want to make some for yourself however, experience is in short supply.
I’ve learned two important production lessons since 2019:
1) Dry flat pieces of lumber work best and
2) As long as you keep feeding new material into a fire from the top as it burns down, the lower charcoal does not turn to ash and become ruined. Let me explain.
Wood needs to be dry to burn efficiently. The basic process heats the wood driving off resins which burn as yellow flames. When the flames are blue and the coals are red, it is time to quench the fire and save the charcoal from turning into ash. Wet wood uses up a lot of the heat to dry the wood before the resins vaporize. It is smoky, inefficient and leaves partially burned material. Wood also needs to be of a fairly uniform size and shape. Sure dead limbs and prunings can make a great fire and even after a time be efficiently dry. But you end up with the small stuff burning up quickly, dropping to the bottom of the fire and turning to ash while the big stuff is still flaming and not nearly turned to charcoal all the way through. It is literally a hot mess.
This is where the local lumber mills make Northeast Washington such a great place. Webley Lumber has a big pile of dry pieces that you can load into a truck and cart away for free. But it is far from the only source of dry scrap lumber. I can think of several neighbors who have their own little sawmills. Running a little sawmill creates a lot of scrap wood and slabs. It is usually too uneven to build with and not thick enough to hold a fire for long in a wood stove. But it is perfect for making biochar because it dries out quickly and uniformly. You can stack it tightly and cut it into short pieces easily with a chainsaw. But remember that part about it burning up quickly in a wood stove? That’s where lesson number 2 comes in.
Many kinds of containers can hold a biochar fire. I use a big metal box once used to ship diesel engines. There are many other ideas at https://wilsonbiochar.com/. A big ring of sheet metal sitting on the ground works. So do old tanks cut open in different ways. The common denominator is that you start a fire in the bottom and add fuel from the top. The fuel burns down to hot coals in the bottom. If left alone the coals will combine with oxygen, burn into CO2 and leave only white ash minerals. This is exactly what you want to avoid. You want to be able to get that nearly pure carbon charcoal into the ground where it will do wonderful things to promote growth and last for centuries.
By adding more fuel on top of the red coals as soon as the previous load has combusted, you heat the new fuel driving off resins which burst into yellow flame and suck up the oxygen before it can get to the red coals. Timing is everything. I use the timer part of the clock app on my cell phone to remind me every 25 minutes to add more fuel. If you add more fuel too soon, it buries the previous load depriving it of oxygen and leaving parts unburned. If you wait too long, coals turn to ash.
You can add a lot of fuel, up to the top of the container each time. As long as it is of an even size and air can reach the escaping gases, it will burn all at once and be ready for the next load. I usually start a fire in the morning and keep adding batches all day until the container is full of coals or it is too dark outside to work safely.
Quenching it is another story. Theoretically you should be able to cut the air flow into the fire and it will cool below combustion point. You could also pour a lot of water on it. Both of these techniques have drawbacks. Even when cool, charcoal is a natural insulator. After being quenched and sealed, I still find hot spots in the embers the next morning. This means that I need to dig through the coals and spray water on them if they are still burning. The other drawback is too much water. Charcoal soaks up water like crazy. It can become very heavy when wet and holds on to that moisture. Also, too wet charcoal creates black goo that plugs up the screen on my shredder when I break it into smaller pieces. Big pieces won’t expose much surface to soil biology. Powder-size biochar won’t hold much water.
I put water or snow on the red coals until they turn black. This involves digging through the coals to expose and drench hot spots. I want the vapor that comes up to smell like steam, not smoke.
So spring is in the air, but not so much in the ground. Seize the moment and make biochar. At least it is a warm project.