Happen to find this thread via a web search for "biochar in potting soil".
In my case, it isn't potting soil but seed starting soil mix. Ran across an attra pdf yesterday called; Potting Mixes for Certified Organic Production
, which is mostly about seed starting mixes and includes recipes from Elliot Coleman and others. They also talk about many possible ingredients including biochar.
What caught my eye:
Research conducted at Iowa State University indicates that screened biochar can be used successfully to replace perlite in greenhouse potting media. The high pH of biochar can also neutralize the acidity of peat and eliminate the need for lime. A mix with 30% biochar and 70% peat moss had a pH and physical characteristics very similar to a commercial peat-perlite potting mix
They mention leaf mold being an old school ingredient which was used the way peat moss is today but leaf mold also has beneficial microbes. I've got some peat here and will probably use it along with some leaf mold/humus, biochar, old compost and homemade bone meal. When I up pot them, it will be more compost plus some aged goat manure.
When I run out of peat, I'll use all leaf mold. Hoping to come up with something that's made with 100% materials from the property. We have goats and any bucklings born this year will be banded and when 70-80lbs, processed and consumed. Food plus blood and bone meal/bone char.
On days that warm up quick, I shut down the wood stove which halts the fire and leaves me with biochar. Not enough to bother with garden use, and where I am, it wouldn't be of any help and might actually hurt. Temperate with heavy soil.
Whatever I don't use to make seed starting or potting mix, I'll save for something. Maybe add it to some compost to be added to a raised bed for carrots that's mostly sand. I can get coarse sand locally at the concrete place.