You can also make biochar in a burn barrel. Just watch the smoke. When it thins, pop on a lid to slow combustion.
One method of making biochar: pile up woody debris in a shallow pit in a garden bed; burn the brush until the smoke thins; damp down the fire with a one-inch soil covering; let the brush smolder until it is charred; put the fire out. The leftover charcoal will improve soil by improving nutrient availability and retention.
ILLUSTRATION: ELAYNE SEARS
Smothering the fire with soil when it was partially burned resulted in lots of charred pieces. When the trench is refilled, the biochar will rest 10 to 12 inches below the soil's surface.
The problem area was once cultivated organic garden, but it's been in weeds and brambles for 5 years. I'll use a thick mulch and winter squash to weaken the unwanted ones for a season before digging them out by hand.
One of two winter squash beds on the slope is an experimental biochar bed. After digging out a 10-inch deep 2x6-foot wide trench, we filled it with seed-bearing weeds, brambles, and other materials we didn't want in the compost.
Biochar can be collected from half burned campfire wood.
We had enough stuff to do a second smolder, so the winter squash in the smoking bed will grow atop two layers of biochar – plus the compost I'll add as I prepare for planting. A few feet away, a second bed will get an equal share of compost, but no biochar. I'll report back in the fall on how they do.