This weekend the permaculture design course I’m attending spent a day with Mike Feingold at his allotment and community orchard learning various skills. I opted to make artists charcoal and biochar which was really fun and simple to do – here’s what we learned so you can have a go yourself.
What’s the difference between charcoal and biochar?
Charcoal is produced when wood and organic matter is heated without the presence of oxygen in a process called pyrolysis.
Aside from lighting BBQs, charcoal is great for building soil fertility. Its porous structure absorbs water and nutrients, holding them in the soil, keeping them available for plants and forms a home for beneficial soil microorganisms. When inoculated with nutrients, charcoal becomes known as biochar. Charcoal is such a stable material that it will last in the ground for thousands of years locking up carbon. It’s a little counterintuitive that burning something could be good for the environment but charcoals longevity creates a net effect of removing carbon from the atmosphere.
The simple way to make charcoal
A little health and safety to start – you’re working with fire so be careful. Make sure you light fires away from combustible material like sheds, fences, trees and nearby buildings. Don’t leave the fire unattended or you risk it spreading.
This is what Mike refers to as the ‘unapproved method’ of making charcoal. It’s very easy, requires no equipment and as our group found, works very well. To start with we lit a bonfire and fed it constantly on the top with wood and cuttings. This has the effect of drawing the flames upwards, consuming the oxygen around the fire which prevents the wood underneath being consumed by the flames, allowing charcoal to be made by pyrolysis.
When making charcoal for biochar you want small pieces to create more surface area. This means you don’t need large logs – hedge cuttings and garden waste are perfect materials.
Once your resource of material to burn has run out, douse the fire with water to extinguish the flames completely. Make sure the entire fire is thoroughly soaked so that nothing continues to smoulder otherwise you will be left with wood ash instead of charcoal.
How to turn charcoal into biochar
Charcoal is inoculated with nitrogen rich nutrients to create biochar. Failing to activate the biochar in this way will result in it absorbing nutrients from the soil when initially added to the ground. In this situation the charcoal absorbs nutrients out of the soil which has an adverse effect. You can activate the biochar by adding it to your compost pile, soaking it in a solution of compost tea or diluted urine for 24 hours. If you have chickens, you can use Mike’s trick and throw the charcoal into the run.
The chickens will mix the charcoal up with the bedding material whilst pooping and peeing on it. When you clean out the compost from the coop, the charcoal will have become inoculated by absorbing those nutrients.
How to make artists charcoal
The process of making artists charcoal is very simple. We used willow cuttings, but you could even use woody cuttings from your garden. First get a metal tin with a tight-fitting lid – a biscuit tin is ideal. Cut your sticks to length so they fit in the tin lying flat and add sand to fill in any spaces which would otherwise hold air. Carefully place the tin in the fire and continue to burn, adding more wood on top for a couple of hours.
Once the fire is over allow the tin to cool down completely before opening, otherwise you risk combustion beginning as the oxygen makes contact with the hot wood. Try breaking a stick to see if the pyrolysis is complete. If the charcoal breaks easily and is black all the way through it’s done. If it’s still a little woody you can reseal the tin and put it in a fire again to finish the process.
Next time you’re getting rid of garden waste why not try your hand at making a little charcoal of your own?