Biochar FAQ’s

What is biochar?

Biochar is charcoal made in modern technology, from sustainable resources and is used for any purpose that doesn’t result in it breaking down rapidly back into CO2, like burning it as  fuel. For a good review of what biochar could be used for. “55 uses of biochar and counting…..”

Biochar is a charcoal-like substance that is manufactured from sustainable resources, using  clean technologies and which is used for any purpose  which does not involve its rapid mineralisation to CO2.

Can all charcoal be used as biochar?

Yes, although we would only call it biochar if it fell under the definition above. Be careful, as there is a wide range of charcoal quality on the market and some are not suitable for food production.

Most charcoals are made from natural organic material, while some more commercial charcoals, charcoal briquettes in particular, contain additives and are not suitable as soil improvers. In particular, we caution against using untested charcoal as biochar to grow food.
Always know where your biochar has come from.

How is biochar made?

Biochar is made by heating organic matter in a container,  with little or no oxygen, the technical term is “Pyrolysis, heating under oxygen-deprived conditions”.

Biochar is made by heating up organic matter in a metal kiln which restricts Oxygen from entering (pyrolysis). For each tonne of wood, 1/3 tonne of biochar is produced, 1/3 tonne of bio-liquid and 1/3 tonne of an energy-rich gas. If the hot gas is recycled back into the reactor, the equipment is known as a retort. By restricting Oxygen, the biomass does not burn to ash as in a garden bonfire. Most organic matter is 45 to 50% Carbon by weight and normal burning in Oxygen releases all this Carbon as Carbon dioxide to the atmosphere. By restricting Oxygen, about 50% of the Carbon is retained in the solid biochar, while the other half is released as Carbon dioxide.

Is it true that you can make biochar using simple equipment in your own garden?

In principle yes. Even a simple tin can or oil drum can be used for producing biochar. Just type “make Biochar” into Youtube.

However, as yet, there are very few demonstrated, safe and effective small scale units that can be purchased ‘off-the-shelf’ as this is such a new industry. But they are relatively easy to make and there are many videos on Youtube that will show you how, just type make biochar into the search bar. We hope the BBF will be able to provide independent reviews of biochar-producing equipment, training on safe and effective production of biochar at the garden scale in the very near future.

What does biochar do?

Above all, biochar is a way of storing carbon for a long time – hundreds to thousands of years depending on where you put it or what it is used for. As we’ve mentioned, other uses are being explored but in two areas the results imply, it could also help with soil ecology and plant growth and aiding digestion efficiency whilst detoxifying from consumption.

When organic matter is added to soils, such as compost, manure or kitchen wastes, microbes living in the soil devour the material for nutrients and energy fairly quickly. Within a decade or so, most of the Carbon has been converted back into Carbon dioxide. When biochar is produced, the Carbon atoms arrange themselves into ring structures consisting of 6 Carbon atoms. These rings are fused together in sheets and the chemical bonds between the atoms are strong – too strong for microbes to break them easily. For this reason, biochar stays in the soil for much longer than the feedstocks from which it is made and removes Carbon dioxide from the air, fixing it securely in soils for hundreds, sometimes thousands, of years.

Biochar can improve many types of soil, making them more productive(but not all).

Exactly how and why it ‘works’ is still being actively researched. Evidence points to the fact that biochar:

  • Enhances plant growth and root development.
  • Contains some nutrients such as potassium, phosphorus and magnesium.
  • Increases microbial life within the soil: this helps to enhance plant growth, through increased soil levels of available nutrients and better disease and pest resistance.
  • Has a very large internal surface area, providing a suitable location for chemical reactions to occur by which important nutrients are made more readily available to the plant roots in the soil.
  • Reduces fertilizer requirements: biochar seems to be able to hold on to the nitrogen that is added to the soil in chemical fertilisers, releasing the nitrogen more steadily to the plant and reducing nitrate pollution to rivers.
  • Suppresses methane emissions from the soil (CH4, a global warming potential 21 times higher than Carbon dioxide).
  • Reduces nitrous oxide emissions from soil (N2O, a global warming potential 300 times higher than Carbon dioxide).
  • Reduce the loss of added nutrients from the soil.
  • Raises soil pH (i.e. reduces soil acidity)
  • Is able to hold a lot of water and this helps provide water to plants in some drought-prone soils.
  • Reduce heavy metal contamination in the soil (e.g. zinc, lead, cadmium, arsenic) as well as potentially toxic persistent organic chemicals.
  • Increase soil aggregation, improving soil aeration.
  • Biochar may also be used for its water filtration properties.


Despite all these possible benefits, it is still early days in terms of learning about how biochar works and establishing what is the ‘best biochar for the job at hand’. The exciting thing about biochar is that by trying to understand how it works is actually driving forward our understanding of soil ecology in general. The latest research implies that it is all about Eh and not Ph, conductivity and electron exchange.

Do some types of soil benefit more than others from biochar addition?

Yes. For example sandy soils benefit more from biochars water holding ability.

Coming soon: a simple matrix of soil type v. biochar benefits.

Does biochar need to be treated and how best is biochar incorporated into the soil?

No, biochar doesn’t need to be treated but in most cases you will get the best results if you do and not treating it before application could result in a neutral or even a negative effect. The BBF recommends that you do not use untreated biochar because of the potential for a negative impact and the inefficient use of resource. A simple treatment would be;

  1. Add biochar to a water filled container,
  2. Add some plant food,
  3. Add some compost,
  4. Allow it to stand for a week or two stirring occasionally
  5. Strain liquid and use as a feed/compost tea and add biochar/compost blend to your soil or compost.


Untreated and treated biochar is best mixed into the soil by adding it to compost, manure, slurry or some other organic matter and then adding this to your soil as you normally would. Be careful of biochar dust as inhaling this could be dangerous.

For instant and best results from pure biochar, yes it does need to be treated and we recommend adding pure biochar to your compost heap / farm manure, leaving it a month or so and use the compost/manure as normal. The reason for this is that pure biochar can act like a sponge and when added to soils it could soak up the nutrients that the plant needs before the plant can get to them. By adding the pure biochar to the compost / manure you allow the biochar to absorb the nutrients and microbes from the compost / manure before you use it.
Soaking in a water butt full of compost tea is a very good way to pre-treat biochar as well. The compost tea can be made from nettles, Comfrey, worm cast, compost or any other microbe and nutrient rich material you can find.

If you are a farmer or just spreading over a large area and/or are not concerned about pre-treatment, biochar can be used as a top dressing in the normal way, just spread over the soil and allowed to mix naturally. However, best practice would be to plough or till biochar into the soil to a depth of up to 30cm and allow the soil to settle over a short period before planting. Fine granules of biochar are preferable and caution must be taken on windy days as biochar can be dusty (e.g. wetting the biochar or using suitable protection). For purchased biochar blends, please follow manufacturers instructions.

How much biochar can I use?

At the moment there is no research into maximum amounts of pre-treated biochars that you can add to soils. So for now we suggest that users keep to the UK suggested maximum limits for pure biochar of 3kg of biochar per square meter every 12 months.

When using a tested, pre-treated biochar for growing, it is assumed that there is no limit to the amount that you can add to your soil in one treatment as long as it has been pre-treated properly, and provided that you a sensible level of organic addition is intended which also does not exceed desirable levels of nitrogen addition to soils. (Over-addition of organic amendments could result in nitrate leaching into waterways causing pollution. The balance of carbon and nitrogen in the soil and in the amendment added to that soil also needs to be considered). At the present time, we do not know what are the possible limits on biochar + organic amendment addition to soil and it will vary depending on the soil type.

Please keep to the important guidelines below for now until we are able to get the research done to clarify this important detail. For every 5 kg of biochar we use, we carbon store roughly the equivalent of 15 kg of carbon dioxide for hundreds of years (on a life-cycle basis), so the more we can all use the better it is for everybody, for plants and the planet.

When using pure biochar for growing, care has to be taken in assessing any negative impacts of biochar when applied at high doses. There is still a lot of research being conducted around the world into the impacts of biochar when added to land growing food crops and until there is more robust scientific evidence, the BBF suggests that a limit of 3 kg per square meter be used at any one time in the UK but in many cases you will also get a benefit from as little as 0.5kg per square meter. After several months of allowing the biochar to incorporate naturally, you will be able to apply further doses at the suggested guidelines if wanted or required. (Farmers and other commercial growers should calculate the desired application rate with reference to the nutrient content of the biochar, the soil and the intended fertiliser regime).

How often do I need to apply biochar to my soil?

Provided the plant or other organic material used to produce the biochar is from a sustainable source and If it’s pre-treated, then we recommend that you should use a maximum of 3kg of biochar, on 1 square meter of soil, every 12 months. For every 5 kg of biochar we use, we carbon store roughly the equivalent of 15 kg of carbon dioxide for hundreds of years, so the more we can all use the better it is for everybody, the plants and the planet.

At present, experts are debating whether it is better to add larger doses of pure biochar in an one-off application to soil, or whether it might be better to add smaller amounts over a number of years. We will provide updates to this discussion on this forum.

More importantly, at present there is absolutely no data on what the maximum amount of pre-treated biochar that can be added to soils at any one time. This is partly to do with the lack of large scale field trials, so if you have some land, any type will do and would be interested in pushing research forward, do please get in touch.

The half life of biochar is still being investigated, although the current conservative estimate is a half life of 400 years. In other words, if you put 1kg of biochar into your soil, there will still be ½ kg of biochar left in 400 years.

Is it legal to apply biochar to soils?

As long as the biochar is not a waste material(as defined by the European Waste Framework Directive) and has been tested and deemed fit for use, then it can be used on all land types and soils.

It is even possible to turn certain organic wastes into waste biochar. It is, however, illegal to spread this waste biochar (as defined by the European Waste Framework Directive) onto public or agricultural land without permission from the Environment Agency (EA) or the use of an exemption from the Scottish Environmental Protection Agency (SEPA).

The BBF are proud of the fact that the UK is the first EU28 member to allow the carbon sinking of societies waste. 

For commercial use: If biochar is not produced from waste material and is the main product of the production process (i.e. not a waste material as defined by the EU WFD), it may be applied to the soil on a commercial scale provided it meets the requirements of legislation including the EU Water Framework Directive and the provisions of the Environmental Protection Act (EPA) 1990. However, if biochar is produced from a waste product or is disposed or otherwise discarded from another production process, it falls under the waste regulations of the Environment Agency (England & Wales) and the Scottish Environmental Protection Agency (Scotland). While a number of organic substances are exempted from the provisions of the EU WFD, biochar is not currently amongst this list (with the exception of non-processed wastes in Scotland – see SEPA’s Position Statement WST-PSD-031). The EA or SEPA need to be consulted prior to any addition to public, agricultural or horticultural land, even for experimental purposes.

For private gardens and non-commercial use: The above restrictions do not apply. This means that you can buy biochar products that might not be available to commercial growers or you could make biochar in your own garden, from your own garden waste. However, householders are still covered by the requirements of the EPA 1990.

Is biochar safe?

As long as it is stored and used correctly and has been tested for any contamination. Yes, perfectly safe.

Apart from the usual health and safety issues storing and handling a material like biochar it should normally be safe, even in large quantities on a commercial scale. When using or applying pure biochar or very dry blends caution needs to be taken as a fine dust can arise from the biochar. Breathing in very small particles is known to pose various health risks including respiratory diseases and even cancer. Such risks are usually associated with prolonged exposure to small particles through employment, e.g. in coal mining, charcoal production or quarrying. However, for the vast majority of larger biochar applications, a simple face mask would eliminate any risk and constitutes best practice.

Although biochar is not accredited on sustainability or production yet in the UK, there are efforts underway to develop suitable frameworks for testing and certifying biochar as safe for use in soil. These include the guidelines developed by the International Biochar Initiative (IBI) and the European Biochar Certificate of the European Biochar Foundation (EBC), which is already being used by 3 biochar producers in Switzerland. Other professional accreditation agencies operating in the UK may also be in a position to provide appropriate accreditation for biochar and biochar blend applications to soil. In order to be accredited, biochar need to have been tested for their contamination levels and should be fit for purpose under UK law and accreditation standards. But as long as you know your biochar has been tested and contains acceptably low amounts of heavy metals and other potentially harmful contaminants, then it will be safe enough for you to grow and eat food from soil containing that biochar. If you don’t, we suggest that you only use this type of biochar for non-food crops or innovative Carbon storage ideas.

Are there any biochar standards or “quality marks”?

Yes, there are two standards at present, with a third coming shortly. The two are; the EBC(European Biochar Certificate) and the IBI(International Biochar Initiative) and the BQM(Biochar Quality Mandate and a UK standard).

There are two existing sets of guidelines. One is produced by the International Biochar Initiative (IBI) while the other is produced by the European Biochar Foundation and called the European Biochar Certificate (EBC). A Biochar Risk Assessment Framework (BRAF) has been developed to allow a risk assessment of biochar addition to a given soil to be undertaken. The Environment Agency, SEPA, WRAP, Rothamsted Research and Universities of Edinburgh and Newcastle are currently working to produce a Quality Protocol for biochar in the UK context. This is expected to be finalised during 2013.

In June 2012, the first methodology approved by the UNFCCC that could allow carbon credits to be generated from the biochar arena was published. The approved CDM methodology ACM0021 will help to clean up charcoal production in developing countries along with existing biochar projects that are using traditional technologies – which should help the biochar arena as a whole.

At present the CDM methodology is quite limited in its scope and focuses on small scale, community-based clean charcoal production. It is possible that in the future it could be developed and refined further, as well as other methodologies along similar principles

How do we know the feedstocks for making biochar are sustainably sourced?

At the moment we don’t but in the next few years, there will be a framework to ensure that all large-scale UK producers meet sustainability criteria for biomass that are being developed by the Government.

The European Renewable Energy Directive (RED) specifies that biomass cannot be used for producing liquid bio-fuels unless it reduces greenhouse gas emissions across the life-cycle (i.e. including growth phase, transport, processing, etc.) compared to the petrol or diesel it is replacing by 60% or more. Furthermore, biomass from land with a high Carbon stock or biodiversity value may not be used.

The UK government is currently proposing a similar framework to ensure that solid biomass used in the UK for bioenergy is sourced sustainably. This will require that a power or heat & power generator of a 1 MWe capacity and over must meet sustainability criteria to receive support under the Renewables Obligation incentive scheme and provide a statement of independent verification. It is proposed to expand the sustainability criteria to include sustainable forest management.

Some people say biochar will lead to tropical rain forests being chopped down – is that possible?

Yes, unfortunately there is a chance that this might happen. This is why a quality standard ensuring the sustainability of resources as well as of biochar production is so important. The BQM will address this sustainability issue.

One of the most obvious problems with biochar is that vast monocultures of fast-growing tree plantations would be needed to provide the raw material if biochar were to be implemented on a large scale, potentially leading to an increase in deforestation. The biochar community is very cautious about the deployment of biochar on a large scale. Organisations such as the IBI, the EBC and the BBF are in place to ensure the sustainable deployment of this new technology and establish international and national standards. One option to avoid deforestation resulting from a rising biochar market would be to buy local biochar only, at least until a reliable standard or certificate is in place. As always, it is important that you know where your biochar comes from.

Is biochar the same as terra preta?

No. Terra preta are highly fertile soils found in South America, they have taken centuries to become what they are today. Biochar was found in those soils and by adding it to our soils over here in the UK, we are hoping to start that process off. Although we will never have true terra preta we should hopefully be able to achieve something similar over time.

What is the “carbon cycle” and what’s wrong with it at the moment?

In short, its how the planet breaths and keeps us all alive. All plants and algae on the planet absorb carbon dioxide (CO2) from the atmosphere and let out oxygen. Because we’ve been using vast quantities of fossil fuels for the past 200 years, in the process adding 0.5 trillion tonnes of CO2 (500,000,000,000 tonnes) to this breathing cycle and not planting enough trees to compensate, there is too much carbon dioxide in the atmosphere. This extra carbon dioxide is acting like a greenhouse window (greenhouse gas), letting the sun’s warmth in but not letting a lot of warmth out and as a result the world is heating up. Global warming.

Carbon begins its cycle in terrestrial ecosystems when the plant assimilates Carbon dioxide from the atmosphere and turns it into carbohydrates through photosynthesis. Some of these carbohydrates are used as energy for metabolic reactions (including plant respiration, which releases Carbon dioxide), the rest are stored in the plant as biomass (leaves, branches, stem, roots). Eventually, the plant material dies and decomposes into organic matter. Decomposing organic matter supports microbial life and emits Carbon dioxide. When it decomposes, most of the Carbon in living forms is returned to the atmosphere as Carbon dioxide within several years. When an ecosystem(the world) is in equilibrium, it absorbs more Carbon dioxide than it emits through respiration, we call it a “carbon sink”. Without human interference, plants, animals and soils managed to keep the Carbon cycle in a nice balance, with just enough Carbon dioxide being taken-up by new growth and just enough Carbon dioxide being generated by plant and animal respiration.

The BIG problem, discovered in the past 30 years, is that scientists have found that there is far too much Carbon dioxide in our atmosphere and that we need to do something about it, fast! The scientists also believe that all the problems started when we stopped using wood as a fuel and started using coal and oil – and when we cleared more forests than we replanted.When you burn coal, gas and oil they produce Carbon dioxide, Carbon dioxide that isn’t part of the “short cycle”, because it has been locked underground for millions of years. So we’ve actually been adding Carbon dioxide to the global Carbon cycle, and this isn’t good for the planet or us. In fact, we’ve added so much Carbon dioxide over the last 200 years or so that we have temporarily upset the balance of the Carbon cycle. In short, there is too much Carbon dioxide in the air and this acts as a greenhouse gas, heating up the earth. So for the past 15 years the questions have been “how do we stop depending on fossil fuels and reduce our Carbon dioxide emissions?” and “how do we take Carbon dioxide from the atmosphere and lock it away somehow, so we can try to balance the cycle again?”

How and why is biochar good for climate change?

Biochar helps to reduce the greenhouse effect by storing stable carbon, that would otherwise return to the air as Carbon dioxide, helping to reduce global warming.

Biochar is made from plant biomass (see Carbon cycle above) that is burnt with zero or little oxygen, only Carbon in its most stable form remains from the plant material. By adding this solid to the soil, we sequester Carbon for hundreds to thousands of years and prevent it from being emitted into the atmosphere by decomposing plants.

What is the evidence that biochar works?

The best evidence suggests that biochar application to UK agricultural lands increase yields by an average of 10%.

Please refer to Jeffery et al. (2011) for a quantitative review of existing trials. These authors present the results of a statistical ‘meta-analysis’ evaluating the relationship between biochar and crop productivity (either yield or above-ground biomass). [link to the Jeffery et al. paper:]

Case studies – examples of where biochar has been used and what the effects were.
Coming soon: Case studies.

How much does biochar cost?

Commercial biochar grades and biochar blends vary considerably from as little as £1 per kg right up to £15 per kg.

As of 2012, it can cost a producer from as little as £20 per ton to £200/300 per ton to produce plain biochar from a traditional charcoal kiln. Once the market develops, biochar producers will opt for cleaner pyrolysis machines.Production Cost is sensitive to the scale of production (larger using cost less per tonne) and to the need for maintenance and labour. As biochar develops, technologies for its production should improve and higher value be obtained from the three by-products of pyrolysis: liquids, gases and the solid biochar. The costs of production are expected to come down over time as a result.