The International Biochar Initiative conducted a worldwide survey of what folks are using to make biochar and created this cool word cloud to summarize the results. For those that haven’t been exposed to the world of word-clouds yet, the way to interpret it is that the larger the font size, the more people that indicated that is the feedstock that they use for charring. Some places in Africa are making briquettes out of things like invasive aquatic plants. This makes tons of sense in places where labor is not too expensive, but it’s probably not economically viable elsewhere. I wish it were as we have a lot more of that in Finger Lakes than we have rice husks, bamboo or coconuts!
So if you want to make some good biochar to test in your garden, what things should you keep in mind when picking feedstock? Although every region is going to vary significantly based on what grows locally, there are a few key things to know:
- Probably the most critical one is that whatever it is, it must be DRY! If you are burning something with a high moisture content (say above 25% or so), don’t be surprised if you get very little char for your efforts.
- Another thing to keep in mind is that biomass with more ‘body’, will likely net you more char (kind of intuitive really). So while stuff like grass, leaves, sawdust, and straw can make char, it’s easy for it to turn to ash quickly. Best to concentrate on the tougher stuff such as wood, wood chips, pits, nuts, etc.
- Uniformity of size makes for easier processing after you’ve made char, so this is way things like wood chips and pits are somewhat easier. Using big pieces of wood means you’ll have to crush it up before you can put it in your soil which causes all sorts of dust if you don’t wet down the char.
Some of my favorite feedstocks include walnut shells (after the squirrels have had their way with them!); seed extracts (although these have a market value as a feed supplement so biochar is not the best use of that ‘waste’) and pits. I’d love to know if anyone has any other favorite feedstocks!