Playing with fire . Goggles for the smoke, gloves, and water on hand in case of accidents are all sensible precautions

Biochar is the name given to charcoal that is intended to be used as a soil improver.

It is becoming well accepted that the addition of  charcoal to the soil can do a great deal to enhance plant growth, it also takes carbon out of the atmosphere on a long term basis and so helps to slow global warming.  If enough of us did this, and did it well, we could even reverse the damage we have done to the planet!

Why Biochar is so good.
Charcoal has a huge surface area, and a slight positive electrical charge which means it will hold onto nutrients in the soil. The chemicals will not be washed out of the soil by rain and are available to plant roots.  The charcoal also makes a great environment for mycorrhizal fungi which have a mutually beneficial relationship with plant roots and help boost the health and growth of plants.

This means that you will need to add less to your soil for great crops and beautiful plants and this means a lesser  cost to both you and the planet.

The very easiest way to make charcoal for biochar is to have a bonfire in a pit. The air supply is limited, so instead of combustion which is burning with oxygen you have some pyrolisation – burning in absence of oxygen, which gives you charcoal. Some of the wood will still go to ash, but on the plus side this will help add nutrients to the charcoal.

This process is inefficient compared to a charcoal kiln which excludes almost all air, and wastes the heat from the fuel, but it is far better than a conventional bonfire where all the material goes to ash and all the carbon becomes carbon dioxide.

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Once you have your charcoal you need to crush it, using a spade to slice it up while still in the pit is a good start, but to get fine material you may need to bash or stamp on it in smaller batches.

It is also a good idea to ‘load’ it with nutrients before putting it in the ground, there is a risk otherwise that the charcoal will attract and hold onto the nutrients around it in the soil and hinder rather than help plants. You can either –

add it to the compost heap – it will absorb nutrients as the heap rots and keep nutrients that might otherwise have washed out.

or soak the charcoal with a liquid feed, this could be comfrey liquid, seaweed solution, compost tea or a bought liquid feed (organic).

More sophisticated ways of making biochar  and using the heat.

I have been helping stove designer and biochar expert, Ed Revill, with drawings of his prototypes and on demonstrations and workshops. This is a sketch of his latest system which could provide heating, hot water and cooking for a house. It is not yet in production or certified, but I hope to make and install one soon to help reverse my carbon foot print. Click for a downloadable pfd:

This is a sketch schematic of the latest stove and some add-ons intended to use all the heat before the cool clean emissions finally leave via a flue. There is also a link to a downloadable pdf.

This is a sketch schematic of the latest stove. There are a number of add-ons intended to use all the heat before the cool clean emissions finally leave via a flue. There is also a link to a downloadable pdf.

Biochar stove sketch 

For a huge amount of detailed information and further drawings go to

Where to get biochar if you can’t make yourself a stove

The best way of doing this is to make your own charcoal from garden waste by trading in your BBQ for a stove that makes charcoal as a by-product.  Stoves originally designed for the developing world are available to buy and are a fun and very eco-friendly way of making you lunch or boiling a kettle while you are in the garden or camping.  I’d recommend anyone to get one, I enjoy cooking and eating outdoors and am sure many of you do too.

Buying biochar at £7 a kilo from the garden centre  is the other option.  Environmentally this is a less good option, it will still benefit your garden, but its manufacture, packaging and transportation may well outweigh the carbon you are offsetting with the final product.

Personally I am delighted to calculate how many pounds worth  I have made  when I boil the kettle of cook up a stirfry!!

To make biochar you load your stove with woodchip, crushed up twigs and odd bits of dry garden waste, build a small starter fire on top and use the hot efficient flame to boil a kettle or cook.  Before the fuel is used up completely, tip the remains out onto a hard fireproof surface and put out any remaining flame with water – you should be left with a small pile of charcoal. Crush it to small bits and add that to you compost or incorporate into the soil when planting.

Stoves which make biochar

The stoves  most readily available for sale are ‘Top Loading Updraft’ stoves – known as TLUDs and sometimes as wood-gas stoves.  I link below to companies where you can buy these stoves.

I have no commercial interest in promoting them – I’d just like more people to share the benefits and get more carbon out of the atmosphere.

For the latest invention – a biochar rocket stove follow this link

The stoves featured are not yet in commercial production, but if you can build one from the diagrams and instructions they will reward you with lots of heat and biochar.

There are moves to set up a crowd funding effort to raise money for a commercial set up to manufacture these and put them into wider use – watch this space.


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