How to Make Biochar with the Biochar-Making Fire Pit

Thank you for choosing the Biochar-Making Fire Pit! Your purchase gives you a sustainable way to heat and cook outdoors while turning your own yard waste into biochar — a valuable soil amendment that improves soil fertility, increases water retention, and sequesters carbon dioxide in your garden.

What Is Biochar?

Biochar is a stable, charcoal-like material made by burning plant matter (biomass) in a low-oxygen process called pyrolysis. Mixed into your garden, biochar acts like a sponge for water and nutrients, gives soil microbes a place to live, and locks carbon into the ground for hundreds of years. Making your own biochar at home saves money and avoids the carbon emissions of buying and shipping it.

Your Biochar-Making Fire Pit Is a Backyard Biochar Kiln

The Biochar-Making Fire Pit is a simple backyard biochar kiln. Instead of sending tree prunings, dried corn stalks, and other yard waste to the landfill, you burn them in a top-down, low-oxygen fire that converts the biomass into biochar — then quench it with your garden hose. You get an outdoor fire to enjoy and a batch of garden-ready biochar from material you would have thrown away.

Watch a short "how to make biochar" video: https://youtu.be/4rSbcE5I4sQ

How to Make Biochar: Step-by-Step

Check burn rules: Check with your city, county, or other jurisdiction to ensure burning is permitted.
Prepare the fire pit: Make sure the Biochar-Making Fire Pit is on stable, fire-resistant ground, placed a safe distance from structures and other flammable material. Verify your hose is working and attached to the fire pit.
Collect biomass: Gather biomass (wood, prunings, etc.) from your garden. We have successfully made biochar from garden "waste" such as tree prunings, dried corn stalks, and dried berry vines. Choose yard waste that is as dry as possible — it keeps the fire burning easily and reduces smoke. You can also use plastic-free cardboard and other compostable waste, as long as the moisture content is low.
Build your fire base: Start with a loose layer of small twigs and dry leaves at the bottom of the fire pit. You can also use paper or plastic-free cardboard as tinder. (New to fires? A YouTube search for "how to build a campfire" will get you on the right track.)
Light the fire: Light it as you would a standard campfire.
Manage the fire: As the fire builds, gradually add larger pieces of biomass. Use small-diameter sticks or kindling until you have a hot base — usually 10–15 minutes. Adding biomass that is too large too early can bury it before it fully converts to biochar. Cut wood to no more than 2 inches thick; anything thicker risks not fully transforming into biochar.
Continue to add biomass: As the fire burns down, it makes room for more biomass — when the flames die down, it's a good time to add fuel. Unlike a traditional fire pit, you'll see biochar start to accumulate in the Biochar-Making Fire Pit. As you near the end of the run (~30–40 minutes), use progressively smaller-diameter biomass, since larger pieces take too long to convert. (Hint: roasting marshmallows and making s'mores before quenching is a great way to pace yourself and avoid quenching too early.)
Extinguish the fire: When enough biochar has accumulated that you can't add much more biomass, wait until the fire has burned down and is no longer flaming. Quench from the bottom up by turning on your garden hose connected to the quenching pipe. Don't let the fire pit overflow — hot material could flow out.
Drain the fire pit: Once the fire pit is completely quenched and nothing is burning, drain it where it stands, or route the water to another part of your garden using the hose attached to the fire pit.
Mix your biochar into your compost: This isn't required to sequester carbon or for long-term soil improvement, but it helps next season's growth. Biochar is like a sponge for nutrients, so charging it with nutrients and microbes from your compost lets it help your garden right away.
Leave your biochar in the compost for a month: This gives microbes and nutrients time to soak into the porous biochar structure.
Add the biochar to your garden: Unlike most fertilizers — where the biggest gains come from treating your best soil — biochar improves the soil and will improve the properties of your worst soil. (Hint: if some biomass didn't fully convert to biochar — it won't break apart easily with your fingers — let it dry out and add it to your next fire.)

Important Notes

The biochar production process typically takes 2 to 3 hours with wood, but can be much faster with quick-burning, small-diameter biomass. For example, we have made biochar with corn stalks in a total run time of around 30 minutes.
The quality and texture of biochar can vary depending on the feedstock and burning conditions.
Local regulations regarding open burning may apply. Always check your local burn rules before using a Biochar-Making Fire Pit.
If you want to make biochar with corn stalks or other dried biomass, preparation is key. Have all the fast-burning biomass prepped and ready to go — with such fast-burning material you need to act fast to keep the fire properly stoked, and you won't have time to collect it while burning.

Troubleshooting

Under-charring

Note: If you don't get full conversion to biochar, set the charred wood aside to dry out and add it to the fire pit next time you make biochar.

Under-charring is typically caused in a few ways:

Putting in a thick stick right at the beginning and then covering it so quickly that the hottest burn zone moves up past it before it fully converts. You'll know it didn't convert because it won't crumble and will retain a strong wooden core.
Putting in wood that is too thick near the end of the run, or too thick in general. We recommend splitting wood to a maximum of 2 inches in diameter. You might get away with thicker, but this is a good starting point — don't put in anything much over an inch in diameter when you have about half an hour left.
Quenching too quickly after adding new wood. Generally don't add new wood for the last 15 minutes. When you quench, you should see very few flames. Tall yellow flames mean synthesis gas (formed during pyrolysis) is still coming out of your wood. Biochar doesn't make tall yellow flames, but wood transforming into biochar does.

Too Much Ash Formation

Using wood that is too long, so that instead of building up layers it sticks out the top of the fire pit and lets air channel down to the char bed. Cut wood to a length that lays horizontally and forms an even layer for less ash.
Leaving your fire pit burning for too long. But don't rush it — roasting marshmallows after the flames have died down is a good way to pace yourself and prevent under-charring.

Water Not Draining

Note: we recommend letting the Biochar-Making Fire Pit drain overnight before troubleshooting drainage.

Water not draining can be caused by several factors:

Airlock: Hose airlocks happen when an air pocket in your hose stops water from flowing out. Picking up and moving the hose can clear the pocket. If that doesn't work, disconnect the hose at the fire pit to eliminate the issue.
Clogged drain holes: The drain holes may be clogged. Use your hand or a tool to unclog them from inside the fire pit.

How to Use Biochar in Your Garden

There are several ways to use biochar in your garden:

Direct mixing: Mix biochar directly into your soil during planting or bed preparation.
Mixing with compost: For immediate results, inoculate the biochar by mixing it into your compost at about a 50% ratio and leaving it for a month. This isn't necessary for long-term soil improvement or carbon sequestration, but we strongly recommend it if you want to improve your garden in the coming growing season.

For a real-world example, see how one gardener mixed biochar two feet deep into his soil for a supercharged tomato harvest.

Conclusion

Biochar is a powerful tool for a healthy, sustainable garden. Making your own biochar saves money and avoids transportation-related carbon emissions. By improving soil health, promoting plant growth, and offering environmental benefits, biochar is a win-win for your garden and the planet.

Safety disclaimer: These instructions are for informational purposes only and should not be considered a substitute for professional guidance or safety training. Always prioritize safety when working with fire and hot materials.

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