I’ve read quite a bit about it. Works good in sandy tropical soils, not so much in temperate heavy soils.
I did use a little biochar for my homemade potting soil this year. It holds water like perlite and in my case, was mixed with leaf mold and very aged goat & chicken manure.
I wouldn’t try to load my heavy soil with it though.
I get biochar aka charcoal(not chemical laden briquettes) from my wood stove. When I dump the ashes outside, sometimes there’s charcoal left from me shutting down the stove when a warm front comes in.
Ashes from the stove sweeten the soil.
Potash?
We used to save all the ashes and coals from the three wood stoves in the house to spread on the garden every spring. Our soil is the heavy red clay type. Along with the ashes we added cow manure every year, always had great gardens.
Works good in sandy tropical soils, not so much in temperate heavy soils.
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How is it for sandy temperate soils that are acidic? Actual soil is thin, as well.
I live just south of the Great North Woods on Old Glacial Lake Wisconsin. We have a fire pit and a supply of oak and pine deadfall.