You asked how to make biochar - this is my current method, including my crazy biochar charging method for maximum nutrients.

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I have have seen many biochar-making systems ranging from cones to kilns to burning wood in a trench. Biochar is really just charcoal with a fancy name, and there are many traditional charcoal making systems which are usually labor-intensive.

I don't have time for all that. I need a lot of #biochar for my garden and I need it for spring.

Having seen the "Kon-Tiki" biochar cone method developed by Dr Paul Taylor and Hans-Peter Schmidt, and Steven Edholm's trenching method, I decided to dig a small conical pit in a sandy area out back and burn biochar in it. We don't have the resources to go making a big metal cone right now and for the scale we need, it's probably unnecessary, though I would love to have one. So we're going the free route and digging pits to burn in. After doing so and creating multiple batches in a short time, I turned the process over to my children to do and now I hire them to make biochar for our gardens.

It's really quite simple to make biochar this way.

First, dig a nice little pit with sloping sides within reach of a water supply. Our pits are a couple feet deep. Then gather your fuel and cut it into short lengths that will fit nicely in the pit. Branches around an inch to an inch and a half in diameter seem to work best. You're going to need a good pile of these. Gather some small sticks as well for the first stage of the fire.

Now get some paper or pine needles or leaves or itty bitty sticks or whatever you have and put it in the bottom of your burn pit and light it. As it fires up, feed it small sticks. Once these are flaming, start to add larger ones.

It makes sense to progress in layers. What you want is to get one layer burning well and turning black before adding the next layer on top. Keep the layers flat on top of each other, encouraging the fire to burn to the edges of the pit. Each successive layer chokes off some of the air from the one beneath, keeping it from melting away into white ash. Add layer after layer until you reach the top of the pit, then give that last layer time to burn until the sticks are glowing red and starting to turn to ash around the edges.

When you hit that stage, soak the fire with water, extinguishing it completely. Don't quit wetting it until you are really and truly sure the fire is out. If it stays lit beneath, you may have the whole thing re-ignite and burn away into ashes while you're not paying attention.
One the coals are cool, get rid of any un-burned chunks of wood you see. There are usually a few sticks that didn't burn all the way down into charcoal.

If you like, you can start crushing the char. I don't bother because it's too much work, though I plan to experiment with some crushing systems in the future.

Now you need to charge your biochar by letting it soak up minerals and/or biological life so it doesn't eat up the nutrients in your soil. If you plow biochar right into a garden bed, it will soak up lots of fertility and render your vegetables very unhappy for a year or more.

I had very good success soaking my biochar in Dyna-Gro, which is a balanced liquid fertilizer used in hydroponic growing. It has 16 elements in it which provide all that a plant needs to grow.

I'm also adding Neptune's Harvest Fish and Seaweed fertilizer to get extra trace elements and some biological activity, along with a quart of kelp meal as well as a cup or so of pink Himalayan salt. All the minerals of the ocean right here.

You can charge your char with a variety of things, including soaking it in manure tea or urine. You can also take the long approach and add char to your compost pile, letting it absorb lots of nutrition while also being colonized by bacteria and fungi. With my last batch of biochar I dumped the charcoal into a drum of Dave's Fetid Swamp Water, which is an anaerobic compost tea I make regularly. It's free, and you can learn how to make it in my book Compost Everything or in some of the other videos on this channel.

Make sure you soak your biochar for a couple of weeks at least, then you can spread it on your garden beds and fork or till it in.

(Full disclosure: I get a commission if you buy through one of my Amazon links, but it doesn't cost you any extra.)