Backyard Biochar
I was going to write a post today about the basics of composting, but then I realized: modern compost should include some biochar — but where are people to get that? A very few plant nurseries have begun to make biochar available to their customers, but most have not yet seen the light. The only alternative is it make your own!
Biochar is simply charcoal that is ground very fine. It makes a good home for soil bacteria, improves the availability of nutrients to plants, and helps retain water. When produced commercially or even large-scale home production, it can also sequester carbon and help reduce global warming. Using the methods we are going to describe here are much less efficient, but they may still be considered slightly beneficial to the carbon cycle. You need to burn wood or charcoal to produce the biochar, which releases carbon-dioxide into the atmosphere — a major cause of global warming. But in nature the wood would have rotted away, releasing that same carbon anyhow. If you use ‘charcoal briquettes’ there is no real charcoal, it has several ingredients but may include coal, which is contributing to global warming — but your biochar probably offsets that enough to be ‘carbon-neutral’ — neither adding-to nor reducing the total CO2 in the air, when all things are taken into account.
If you have real charcoal — made from wood — you could simply grind that up into a powder and use it as biochar. That’s a lot of work, and you don’t get to enjoy the ‘magic’ of seeing organic material turned into biochar, but it is one option a lot of people are using. Find a hard surface at ground level (a bowl-shaped depression is best if you have one, since it keeps things together) — put some chunks of charcoal on it, then pound with something like a long 2 x 4 or an old wooden post. When there is nothing but powder left, sweep it up — that’s biochar.
More interesting is to make your own. You want to start with an organic material that will crumble easily after it is converted to charcoal. I’ve used horse manure, leaves, and straw, those all work fine. Be sure your material is dry — you could use green leaves or other wet material, but it takes much longer (because the water has to be driven-off first) and so wastes fuel. This could provide a way to recycle your household pet-manure, though I haven’t figured any easy way to let that dry without creating an odor problem (reader suggestions welcome). Sawdust would probably work well for making biochar, if it comes from wood that hasn’t been treated with chemicals or bonded with glues (like plywood).
Look around and see what you can find — any organic material that is dry and crumbles easily will work, so long as it doesn’t have any toxic or poisonous compounds in it. Then find a container to cook it in. I use a five-quart enameled pot. Don’t use aluminum — that will melt — steel or iron will work best. Be sure it has a loose-fitting lid. As you heat the organic material it will give off gasses — those must have a way to escape. A perfectly closed container would explode. If you don’t have a lid too much oxygen will get to your material, and it will burn to a white ash — not charcoal/biochar.
Then, next time you have a barbecue, simply use your left-over coals to heat your biochar. It takes about 45 minutes for my five-quart pot, figure more or less depending on how big your container is. Here is a picture of my pot at work:
Making Biochar on the Back-Yard Grill
Notice the flames coming out around the lid — that is the gas I mentioned. When you heat organic material it first gives off any water vapor, then begins to release flammable gas. In commercial production that gas may be captured for use as a fuel, or it can be re-routed back under the biochar container to make the process more efficient. Here it just burns off — but it’s a great chemistry lesson for the kids. When those flames stop, your biochar is probably done.
Let the pot cool completely before opening — the material may catch fire and burn if you let a lot of oxygen in while it is still hot. Then just stir it up to make it crumble into a powder, and you have your own home-made biochar. If there are parts of the material that didn’t blacken completely, and have not converted into charcoal, you can set those aside to add to your next batch.
Add this biochar to your soil or better-yet to your compost, and you will see an improvement in texture, water-holding capacity, and plant growth. It will work on the farm, in your garden or the flower-pots in your house. Up to 15 to 25% by volume is best for your compost. The biochar will help the compost work faster, with less odor.
This is not a fertilizer, your soil must be highly fertile or the biochar needs to be used in combination with organic fertilizer (hence the compost). Biochar makes the fertilizer more effective, reduces pollution from run-off, improves crops and sequesters carbon — what’s not to love about that?