Make biochar in your home garden - Part 2
The perfect home for little animals, microorganisms and fungi in the soil? Biochar, that's for sure! This is where they like to move in. Biochar helps them store nutrients and water. The perfect basis for making the soil fertile again.
Like a barbecue, just different
Making biochar is like grilling, but a little different. Instead of buying barbecue charcoal, we need wood and make something like barbecue charcoal. If you like to grill, you usually enjoy making biochar. What you need for it and where to get it, we wrote in the first article on this topic https://www.bettersoil.info/blog/biochar-at-home/ .
All you need is a good box full of dry wood pieces or branches. The thickness should be about 2-4 cm with a length of about 20-30 cm. Thousands of years ago, people made coal by simply digging a hole in the ground. It is important that the hole is round and larger at the top than at the bottom.
Let’s start – lighting the fire
A kettle grill has a similar shape. That is why it is more practical to use the grill for making biochar in your garden at home. We will talk about making biochar in a different article. In case you already want to have a look, visit our Iran project page https://www.bettersoil.info/projects/tree-planting/ .
Now, let us start with biochar in your kettle grill:
- The first step is to start the fire. This can be done quite easily by stacking especially thin and dry pieces of wood on top of each other, as shown in the photos. To do this, place two pieces parallel to each other with about 10 cm right in the middle on the bottom of the grill. Place two more pieces crosswise on top of the first two pieces, again about 10 cm apart. You can stack the pieces and build the tower until it is as high as the kettle grill, it does not matter that much. With a bit of excelsior in the upper third of the tower, you can light the tower from the top.
Proper firing up
The second step starts when the tower falls over, because most of the wood pieces have started to burn. Now you can add some thicker pieces, not too close, so that the small fire does not go out. This works quite well if the thicker pieces of wood are as dry as possible and three or four logs are laid across each other. Then they get enough air and ignite faster. It is important that everything burns properly so that enough heat is generated.
In the third step, we add a new layer of wood when the thicker pieces of wood of the second layer start to burn less. A good time to add a new layer is when ash slowly forms on the wood of the second layer. This is the sign that the outer layers no longer contain gas. The outer layer of charcoal starts to burn. During this process, you can no longer see flames. Embers are formed. When the heat has released the gas from the wood, the framework of the wood starts to glow. This is great when grilling because it gets extremely hot, but there are no more flames to burn the meat, bread, or vegetables on the grill. When we want to make biochar, we need to avoid the coal to burn.
Biochar – layer by layer
Repeat this step until the kettle grill is full of biochar. Add a layer, wait for ash to form, add another layer, wait for ash to form, and so on.
While the last layers are burning, you can fetch two or three buckets of water, depending on how big the kettle is. We will need this later to extinguish the biochar. Alternatively, you can roll out a garden hose and have it ready.
When the grill is full, let the last pieces of wood burn out until there are only a few flames left on the surface. The rest of the biochar should now be slowly glowing away. Now take a bucket of water and pour it slowly and steadily onto the charcoal. Keep adding water until the grill is full and the top coals are floating.
CAUTION: It is best to put on safety glasses for this. Hot water, ash, sparks, and embers can jump out of the grill.
Of swirls and pyrolysis
The trick to making biochar is to give the fire just enough oxygen to dissolve all the gas from the wood. What remains is the framework of the wood, the carbon. The combustion of wood with the addition of little oxygen is called pyrolysis.
Due to the round shape of the kettle grill, the air with oxygen can reach the fire only from the top. The bottom and sides are airtight. Also, the gas leaks out and starts to burn. The oxygen comes from the top and pushes the flames to the side to the edge. You can see this clearly in the photos and videos. Also, the grill is hot. The air on the walls outside the grill gets hot and rises to the top. Because the grill is round, a ring of rising air forms. Because of this, oxygen can only reach the fire from above. As the air moves up (outside) and down (inside), air vortices form around the edge. If this happens, you have done everything right. Any smoke or fumes that develop are thus blown back into the fire and burned. The less wind there is, the better you can observe the effect. This also prevents toxic substances from settling in the charcoal of the plant, which should not end up in the soil later.
Tricks for professionals
Sometimes the fire (almost) goes out. This may be because the wood is too wet, or you've added too much wood, or the new layer is too dense. You can quickly rekindle the wood by putting wood shavings or small, dry pieces where there are embers.
If the wood is too wet, you can place it on the edge of the kettle grill. This will allow it to dry before you put it in the fire as the next layer. A bit of dexterity is needed here so that the logs don't fall off or directly into the fire.