First up, ask yourself; what volume of biochar do I need?
If you have a few plant pots or garden beds, you can make plenty with a regular camp fire or a metal box or brazier. If you want to add it to your compost pile or back yard garden, you might need something like a bath tub or small TLUD.
Once you start to need more volume than that, you will be moving into large pit burns or something like the Warm Heart Kiln. These techniques will make hundreds of litres per burn, but you will need a lot of dry biomass ready.
Can you light a fire to make it where you live? If not, maybe it’s best to just buy some biochar. Don’t buy barbecue charcoal. It may have other things added to make it light easily. Buy gardening biochar.
Do you have plenty of biomass (wood) to make biochar with? You will need roughly 4x as much woody biomass as you will get back in biochar. This isn’t loosely stacked biomass. You get about a quarter of the solid material you put in back as biochar so you need a lot more than you think. This is why it can be good to start small. Avoid anything with nails as you will not want them in the biochar and regret it later.
You really don’t want to be paying for woody biomass. Garden pruning (branches) are great, bamboo is ideal. It needs to be dry, very dry. And it needs to be cut up into pieces that suit the way you will make it. Straight-ish pieces are good as they lie on the bed of embers nicely. Small pieces suit smaller methods, but don’t make too much work for yourself. Dry wood is harder and more work to cut. Best to cut it up when it’s wet and then let it dry for a few months.
You probably don’t need to go all the way to chipping the wood. Wood chips can be made into biochar but it can be difficult to get them to char effectively without more handling, so stick to sticks. Ideally nothing bigger than your wrist. Bigger pieces will take a long time to char and by the time they do, lots of other good charcoal will have been lost to ash.
Pick a good day for the burn. A calm winter day is great as you will appreciate the heat. No strong winds, no distractions. Several times I have gone off to do other things and come back to a pile of ash. This wastes a lot of work.
Allow several hours. My burns usually take at least 6 hours so I start early. Have everything ready from the night before. Especially the water to put out the burn or avoid any out of control fires. I do my burns within a few meters of a powerful hose, away from trees, machinery, animals, buildings long grass etc.
When you have enough glowing coals, or are just tired, put it out thoroughly. This means completely soaking the embers, not a light spray with a hose. I absolutely flood the fire with water because I have lost a lot of biochar over night when it has not been put out properly and turned to ash.
Leave it overnight then drain off the water the next day. It will all be cooler and safer to handle.
Depending on what you are doing with it, you may not need to crush it, but laying it thinly on a hard surface (concrete driveway) on top of a tarp and driving over it works pretty well. Crushing it wet will also avoid much of the dust. It’s tempting to use a wood chipper but it can be very hard on the chipper getting powdered dust into all its workings.
Take your time on the first few burns. At this stage you’re learning the techniques.
