Thanks for the link @Indio! I just checked it out -- great video. My main takeaway is that I need to learn more. I've read such conflicting things about biochar -- what it does, how it does it, how to make it -- that I'm confused. How do you make yours? Or do you get it somewhere? What do you add to it before you put it into the soil?
Allright - I'm dragging up an old topic because I haven't been keeping up with this thread, and I've been making biochar in decent volume for close to a year.
I agree - lots of information online for making your own biochar (charcoal) is confusing, over-engineered or just plain old too much WORK!
Fair warning, I'm stuck at home (PANDEMIC!) and have started in on the whiskey.
So, the basics:
Think of biochar as a rigid, lightweight, extremely porous sponge. When it's produced, it's a totally empty carbon matrix. Everything else was burned out. If you put it in the soil as-produced, it will suck up nutrients and water for a little while (year-ish? Depends on conditions) then after will be a net help to the garden. If you pre-treat your biochar with nutrients, it will be helpful to most gardens immediately.
So, what do you need to efficiently make biochar at home the lazy way?
Dry biological material. If it's wood - mostly not too thick. You can use corn stover, rice hulls, old fence pickets, pallet wood, almost anything - just make sure it's really dry and not too thick.
A container for your fire which will limit oxygen, but let you keep the burn going. Wider than it is tall, preferably with outward-sloping sides
A safe place to have your fire (note: If you're doing it right, there will be very little smoke after you get it going)
A method to quench the fire (I just use water from the hose - but in areas where water is limited, you can smother with wet cloth for less net water usage)
A method to break down the biochar, likely below half an inch ( ~1 cm) pieces
Now, onto some details:
I dug through all sorts of reports/sites/whatnot on biochar, and by far the simplest, most straightforward approach I found was the "flame capped kiln" - basically a container where you can have your fire, but limit oxygen from the bottom and sides.
Example:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=2ahUKEwj_nda5mrnoAhUBOKwKHdvSCX0QFjAGegQIBRAB&url=https%3A%2F%2Fforestry.usu.edu%2Ffiles%2Futah-forest-facts%2Fhazardous-fuels-reduction-using-flame-cap-biochar-kilns.pdf&usg=AOvVaw2yALqjhCh2KX76RDuVS2MzUnfortunately, the described version is too big and heavy for the usual home gardener - and likely too expensive as well!
I experimented with a variety of easy/cheap approaches. It really is critical to have it wider, preferably with outward-sloping sides. A metal 5-gallon bucket is quite finicky and problematic - too tall, meaning not enough air/oxygen. The best cheap solution I found was a steel washtub. Modern example linked below, though a more old-fashioned heavy galvanized (instead of electroplate) version would be better.
https://www.tractorsupply.com/tsc/product/behrens-17-gal-galvanized-sheet-steel-utility-tubThe whole idea is to get a good fire going, burn off the volatile resins from the wood, but leave a pure carbon matrix behind. Enough oxygen to burn the volatiles (make visible flames) but not enough to ash much of the charcoal/carbon matrix. The quickest production is from smaller sticks/twigs, under 1" (2cm) and cut to fit inside the kiln/tub. Of course, I also have larger wood that needs to be processed, but I limit it to 4 pieces of 2-4" (4-9cm) diameter. These larger pieces are used at the very beginning when making a "log cabin" style fire in the washtub to give them the longest possible burning time. I use small pieces between and around them, and periodically lever up the larger diameter pieces to the top of the fire. They also periodically get smacked with the poking stick to break off charcoal and expose the innards to the heat. Too many thick pieces? Split them before you get started!
So, key item: When to add fuel? Ideally, you are adding fuel when the existing burning sticks have blackened and are just starting to show ash. Ash is the carbon matrix burning away, so if you have ash starting - you've gotten most of the volatile components burned off. Add some more fuel so that it sucks up the oxygen and also provides heat to your semi-burnt pieces, driving off the rest of the volatiles.
I reserve some really small diameter twigs/brush/straw for the very end of the burn, because there are invariably a few larger chunks which haven't finished burning, but the rest of the washtub full of coals is going to start ashing away. The little twigs burn fast, using up the oxygen that would otherwise let your precious charcoal turn to ash.
At the point where you have a nice, even bed of coals filling your washtub most of the way and very little to zero flame - quench. Stir your nice charcoal and find the hot spots. Quench again.
After everything has cooled, I use a 1/2" mesh screen to screen out the large pieces, break them up, then rescreen. If a piece is still too big - it probably wasn't cooked enough. I set aside any material which doesn't make it through the second attempt at screening, get it dried thoroughly - and put it in the bottom of the washbasin for the next run.
Post-treatment: Critical item if you want to use this beneficially in the garden in a short timeframe. You need to get nutrients into that barren carbon matrix. You could use compost, manure, chicken droppings, urine... There was a great little study on capturing nitrogen from cow barns - mixing the cleanouts (of manure/urine/straw) with charcoal was better than straight composting at retaining nitrogen. However, the best approach (highest nitrogen retention) was to simply use the biochar spread in the barn to get that direct contact and absorption.
So, how to do this at home the lazy way? Put your charcoal in a 5 gallon bucket in a discreet area of your garden or porch, and add urine.
Where do you get the urine? Well.... make sure to hydrate well with tea, or beer or whatever while gardening. Spend a long time gardening. You don't need to go back inside. *hint* *hint*
Maybe you chicken folks will let me know if charcoal works well as chicken bedding...