Make biochar, there are many guides on the interwebs.
Add continuously to you compost bin along with the normal stuff you put in there.
When the compost is done, add it to the garden.
Note the step of adding it to your compost, not to your soil directly.
The charcoal acts like a sponge for water soluble nutrients in the soil; if you add it to the soil directly, it will suck them out of the soil first, temporarily depleting it. Long term it acts as a reservoir, but you want it to go into your garden full.
The charcoal acts like a sponge for water soluble nutrients in the soil; if you add it to the soil directly, it will suck them out of the soil first, temporarily depleting it. Long term it acts as a reservoir, but you want it to go into your garden full.