GeologicalForms said:
Biochar is pretty expensive but the semps do like it, you can collect your own charcoal from the fire pit (which works fine) but to make a similar substance to the biochar sold at nurseries you'd have to remove the dust and boil then dry it, I've heard that "activates" the charcoal so it's nutrients can be more easily absorbed, but I just throw mine in there raw at 1/9th of my mix.
Charcoal needs more than that to activate it for it to be biochar. It first needs to be wet down, because it is resistant to water. After that, it needs to be "activated" by placing other stuff in it - compost is great, but other popular things include molasses, urine, flour etc. This allows the charcoal to become a "condo" to nutrients that microorganisms can thrive on. Adding straight charcoal to your soil will eventually become biochar, but to do so it will leach nutrients from the soil which will take them from the plant.
https://www.ars.usda.gov/midwe...
I make most of my biochar from the charcoal in my wood fireplace. Works great.
