Make Your Own Biochar for Soil Health and Carbon Sequestration

Making biochar has so many benefits and it’s fun to make on the farm. We attended a biochar workshop with Dennis Enright from New Zealand Biochar Ltd earlier this year and walked away with a simple plan to make a kiln.

Because we are so excited about biochar, we want to share it with others via this blog article. We have also organised a webinar with Dennis Enright in June 2020. Scroll further down for the link to the recording. It’s 1.5 hours long and well worth watching.

In this post we will mainly discuss the creation of the “flame cap” kiln, how we make biochar at KoruKai Herb Farm and ways to activate the biochar before adding it to your garden (this is also part of the webinar).

Before we made the kiln we used a small biochar burner for a few years that makes biochar through pyrolysis in an oxygen deprived chamber. It is a great method on a small scale for an urban garden and is easily done at home if the house has a log burner.

Biochar chamber within a fire. Biochar is created inside of it and gases are released through the hole and burn off.

During Covid lockdown in April 2020, we spent a pleasant afternoon making the kiln and had our first burn as soon as the fire ban was lifted in May.

DIY Biochar Kiln

Here the plan for an easy DIY kiln to make biochar using the “flame cap” method.

The material costs are between $60 and $100 depending on the thickness of the steel.

Measuring and marking the cutting lines on a 2.4 x 1.2 metre steel sheet. We chose 1.2mm thickness, but 0.8mm is also sufficient.
Kai cutting out the shape with an angle grinder.
Drilling holes into a flat bar and into the kiln.
Bending and connecting the steel edges.
Attaching the flat bar with screws.
Taking the sharp corners off with a steel file.

Feedstock for Biochar Production

A large range of materials can be used to turn into biochar. It is called “feedstock”. It is best to use what you have available in your local area or right on your farm to avoid transport costs and lessen the environmental impact. No point transporting biomass from one place to the next and burning fossil fuel as we go. Feedstock needs to be dry, free of chemicals, untreated and should not be thicker than 7cm.

Farm “waste” like hedge or fruit tree prunings, coppicing material (willow, poplar), logging residues and dried animal manures make great feedstock and are readily available on a farm. We add shells and bones in small quantities to a biochar burn. This process releases their calcium and they make excellent biochar. Crop residues like nut shells, fruit pips, straw and rice hulls are also great to use.

The Biochar Burn using the Flame Cap Method

This video shows you how to start the fire and how to maintain the burn during the biochar creation using the above kiln.

We love bonfires and spend many evenings throughout autumn, winter and spring sitting around a fire. Now instead of having a regular bonfire, creating pollution and ash, we now use a biochar kiln and make biochar as we go. We can also use the heat to bake some stick bread or heat up a meal.

Beef strew for dinner.
Using the heat for cooking.
Cooking some stick bread.

Quenching the Burn

Once you run out of wood, the kiln is full or you simply want to go to bed, you have to stop the burn. If you do not do this last step properly you come back to ash the next morning.

The easiest way is to hose it down and cool the top layer, then tip out the contents of the kiln and keep applying water until it stops sizzling, steaming and there are no more hot spots. You can also cover everything with soil and quench it that way. When making the biochar in a pit, you can also fill it up to the top with water.

Activating Biochar

Biochar has a highly porous structure, making it a giant sponge which soaks up water, nutrients and invites microbial colonisation.

Close up of biochar showing its porous structure (image:

The activation process “pre-loads” and inoculates it with water, nutrients and microorganism. If this is not done before application to the soil, this process happens within the soil, taking away nutrients, water and microorganisms which may result in poor crop performance in the first few months.

There are a few ways to activate biochar and they are all pretty simple to do:

  • Stomp it into small pieces and feed to cattle. The char travels through the digestive system and lands on the grass perfectly activated within the cow pad. We use about 10% as part of our daily mineral mix of seaweed powder, molasses, crushed garlic (great wormer), apple cider vinegar, sea salt, sulfur, lime (for calcium as our paddock is lacking it) and 2 cups of crushed barley. Get them slowly used to it and start with small amounts and then increase week after week until you get to about 5-10% within the mix.
  • Mix equal parts of fresh cow manure and biochar. Keep it wet and let sit for 1-2 weeks.
  • Urine activates biochar. We use biochar as part of our compost toilet. It keeps odors down and gets activated in the process.
  • Add it to your compost pile at 10% by volume while constructing it. When the compost has matured the biochar is activated and gets spread into the garden as part of the compost.
  • Mix equal parts of vermicast or compost with biochar. Keep wet and let sit for 1-2 weeks.

All of the above processes colonise the biochar with water, nutrients and microorganisms. Once it is mature it can then be added to the soil. We use it in the vegetable garden, the food forest, around fruit trees and in the paddock.

Webinar Recording

Below is the recording of the webinar from 2nd July 2020 with Dennis Enright from New Zealand Biochar Ltd. and Cornelia Holten from KoruKai Herb Farm (Duration: 1h 23m)

We hope you enjoyed reading this blog and it sparked some interest in you.

Here are some useful NZ websites with more info on biochar:

• Biochar Network New Zealand:
• New Zealand Biochar Ltd:
• AllBlackEarth:
• KoruKai Herb Farm:  – Blog

Comment below for questions and further ideas.

Biochar making at KoruKai Herb Farm, Banks Peninsula, New Zealand.


  • Mike Stewart-Jacks
    2 October, 2023 at 3:46 am

    Very helpfull webinar recording, thank you for the time and effort to produce it. I particularly appreciate the dimensions and plans from the 2.4m x 1.2m steel sheet. I’ll get started on one next week!!
    Thank you,

  • Susan Morrison
    4 April, 2021 at 2:11 am

    Hi your video on making the fire on your blog doesnt seem to be working would it be possible for you to reload

    Many thanks

  • Frank Strie
    4 October, 2020 at 12:51 am

    Thank you Cornelia to your family and the NZ BIOCHAR Network
    This is a superbly written article and the photos are so valuable as they show how the whole family is involved in the process and carbon action. You highlighted how the thermal energy can at least partly utilised for boiling water and cooking food and all the outdoor fun this entails.
    I am sure that my family clan and our 4 Grandchildren and their friends will take inspiration from this.
    When the opportunity may allow us to travel New Zealand some day, Karin and I will be keen to call in for a visit and conversation about our Biochar experiences in Tasmania and New Zealand.
    Thanks again and best wishes

    • Cornelia Holten
      8 October, 2020 at 8:16 am

      Thank you for taking the time to write your thoughts on this. We would love to have you over sometime when you are able to travel again. I personally loved spending time in Tasmania when I was backpacking over 17 years ago. Shows me that I am getting old with my 20s so far away 🙂


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