While biochar is very similar to charcoal, there are a few key differences to pay attention to.
We were motivated to write this after we saw a popular gardening YouTuber telling people to go and buy lumpwood charcoal from a local hardware store and add it to compost to create biochar.
They failed to mention all the potential risks and hazards associated with doing so and what you need to do to avoid them.
If you’re not careful, you could be putting yourself at risk of buying petroleum soaked charcoal made from tropical rainforest deforestation. Not only is this bad for the planet but it can also harm your soil.
If you source sustainable charcoal, can you use it as biochar?
To answer this, let’s explore what makes charcoal different from biochar. Here we break it down into 4 main categories.
One major difference between charcoal and biochar is the temperature at which it is made. Charcoal is made at roughly 400 degrees Celsius whereas biochar is made between 600–1000 Celsius. Making biochar at lower temperatures causes volatiles (smokeyness) to be left behind, which has been found to limit plant growth.
Temperature also affects the porosity – the higher the temperature the higher the porosity. This means charcoal isn’t as effective as biochar at holding onto water and nutrients. Less pores also means less surface area for microbes. So using crushed up charcoal instead of biochar won’t work as well for your plants.
The lower temperature of charcoal making also results in a less stable form of carbon, meaning it won’t provide the long-term carbon sequestration properties associated with biochar.
Research shows that carbon, naturally occuring in wood, turns into a crystalline structure at higher temperatures. Meaning charcoal has a shorter lifespan in the soil compared to the hundreds, possibly thousands of years that biochar remains in the soil.
So it’s not as good in the soil and it’s not as good for the planet. Biochar made at higher temperatures performs better and sequesters more carbon, so next time you’re looking to buy biochar, try and find out how it’s being made so you can be sure you’re getting high quality stuff.
95% of the BBQ charcoal we use in the UK comes from abroad. A lot of this is made from tropical hardwoods like maple in a terribly polluting process. They go into the rainforest, chop down trees , put them in a pile, cover them with dirt then set them alight. This creates huge smoke clouds which mostly contain methane (methane is 25x more potent than CO2 as a greenhouse gas).
Making charcoal from hardwoods, like maple, makes it much harder to light. The denser the wood the harder it is to set alight, this is why they pour on petrochemicals before they bag it up. Do you really want this in your soil or your food?
When you buy a cheap bag of lumpwood charcoal and use it for biochar you could be contributing to deforestation and climate change.
The other 5% comes from a range of different companies all with different sustainability criteria. Some suppliers work with local woodland management companies who supply the feedstock for their system. By doing this they are using a by-product from another system meaning they aren’t cutting down forests to make their BBQ charcoal. Also by creating an economic case for woodland management it allows work to go ahead which previously would not have happened.
If you google how to make charcoal, you will most likely be told to collect wood, pile it in a mound, cover it with dirt or moss and set it alight. Or you’ll be told to make a kiln from an oil drum. In both cases, smoke is produced and is allowed to release into the atmosphere.
Modern charcoal producers have to flare off this smoke by setting it on fire using a natural gas powered pilot flame. This turns the methane into CO2 reducing its potency as a greenhouse gas. It is possible to condense the smoke and make wood vinegar but very few people are doing this. O
We designed a kiln you can use at home which turns the smoke into heat for you to cook off. You need to use dry surplus wood, nothing wet, and you’ll get an almost smokeless burn. https://www.earthlybiochar.com/products/biochar-kiln-make-biochar-at-home
What makes biochar different?
Biochar producers use pyrolysis kilns which utilise the smoke to power the process whilst creating carbon neutral heat. In this way, no methane is being produced, making the process carbon negative. Smoke is flammable, so by letting it pollute the planet you’re throwing away useful fuel.
Pyrolysis means ‘separation by fire’, and during pyrolysis all the naturally occurring compounds in wood (sap, fats, carbohydrates etc) are driven off by the heat of combustion. What’s left behind is the carbon structure of wood, including the xylem and phloem structures which were responsible for transporting water and nutrients up and down the plant. During pyrolysis 50% of the carbon is released from the wood and 50% remains as the carbon structure.
By using wood that would have ended up in landfills or incinerators, we can intercept 50% of that carbon and prevent it from entering the atmosphere. In the UK, wood which is sent to landfill will rot down producing methane and CO2, and wood sent for incineration will be burned to ash, in both cases, the process releases 100% of the carbon.
Using wood that is destined to rot or burn means we can avoid 50% of these emissions and turn the remaining half into a non biodegradable form of carbon. This is why the IPCC listed biochar as a Negative Emission Technology (NET).
But what happens if we run out of the 5 million tonnes of waste wood the UK creates every year?
Although this is not likely to happen, it is still important to explore and prepare for all outcomes.
Trees reach peak carbon at around 60–80 years at which point some release as much carbon as they sequester. In theory you could plant a forest of fast growing native species on an unused piece of land, harvest them for biochar at peak carbon, then plant new trees to pull out more carbon. Allowing you to effectively harvest carbon from the sky.
However, this is a subject for another blog post. So let’s recap what makes biochar different from charcoal.
- Cheap BBQ charcoal harms the environment and your soil.
- Sustainable BBQ charcoal is better for the planet but isn’t as effective in the soil as high temperature biochar.
- Watch out for rouge biochar producers. Ask your supplier how they make it. Is it carbon negative?
If you want to learn more about this, send us a message on Instagram and we can help you learn what you need to know and if you’re super keen, sign up for our biochar webinar series for a free end to end Biochar education experience. 📖🤓👍
Charcoal and deforestation: https://www.bbc.co.uk/news/science-environment-44880398
High volatile matter charcoal affecting plant growth: https://www.researchgate.net/publication/232114108_Charcoal_Ash_and_Volatile_Matter_Effects_on_Soil_Properties_and_Plant_Growth_in_an_Acid_Ultisol