How to make biochar?

Gardeners must always look ahead. For years, scientists thought of the Amazon River basin as a pristine land untouched by humans with the exception of a few small bands of hunter gatherers. They thought the thin tropical soil was useless for agriculture.

However early Portuguese explorers found areas of rich black earth they called “terra preta do indio,” meaning “Indian black earth” in Portuguese. The pre-Columbian peoples created this rich soil by adding charcoal and animal bones to regular dirt to produce a very fertile soil. When organic material is burned without oxygen, the result is charcoal.

You can do the same with your own garden or farm soil by adding the single vital ingredient of terra preta, charcoal. When used in soil building, charcoal is often referred to as “biochar.”

Biochar can decrease nutrient leaching, lower soil acidity, and reduce the amount of water and fertilizer used on your vegetables and flowers. Charcoal is highly porous and contains many of the nutrients found in the organic material from which it was made. Charcoal increases the soil’s ability to hold onto plant nutrients and beneficial soil microbes by slowing or reducing the leaching of nutrients by rain or watering.

The low density of charcoal lightens heavy soils, which allows better root growth, increasing drainage and allowing air into the soil. Charcoal works the same as agricultural lime to raise soil pH. This all-natural product increases soil levels of available calcium, magnesium, phosphorus and potassium.

You can make your own garden charcoal or biochar. Do this on a calm day with no wind. Because you will use live fire, always have a fire extinguisher handy.

Dig a small trench or hole in your garden or field. Loosen the soil in the bottom of the hole or trench. Add dried leaves, sticks, brush, or any other organic matter to the hole. Start small so you can control the fire.

Set fire to your dried material. Bear in mind that this will go into your soil; never use charcoal lighter, gasoline or other chemicals on the fire.

You want the fire to burn hot and fast at first, and after the initial flames die down a little, bury the pile with dirt to cut off the oxygen. Your trench or hole will now smolder and slowly burn. Keep an eye on it and once the larger pieces are about three inches big, put the fire out completely with plain water. Be sure the fire is completely out. Let the embers cool off completely before adding this charcoal to the soil. Pulverize the charcoal until it is in pieces the size of a pea or smaller. To crush the charcoal, put it in a heavy sack and beat it with a broom handle, baseball bat, or two-by-four piece of wood. Use your charcoal or biochar the same way you use compost or manure. Scatter it lightly across the soil and work it in. You can even add fine charcoal to your compost heap to speed up the composting process. Always use charcoal or biochar with fertilizer or naturally rich soil, or you may slow down plant growth.

Charcoal captures carbon and prevents its release into the atmosphere. Charcoal can retain its carbon in the soil for up to 50,000 years. Thanks to the so-called primitive people of the Amazon, charcoal in the garden can help increase crop yields, reduce water runoff, and let us breathe easier for a long time. Maybe 50,000 years.


Peter Cundall: organic charcoal good for your greens

I’VE always believed the most important resource of any country — apart from ­people — is fertile soil.

This is particularly true of Australia which, while having some rich and fertile soils, also has impoverished areas that require heavy fertiliser applications in order to grow the exotic fruit and vegetables we eat.

As an organic grower, I avoid using disruptive or unnatural chemical fertilisers. Over many decades I’ve proved how easy it is to grow food and ornamental plants successfully using organic methods.

I continually experiment and, in the past few years, have been achieving astonishing results by using enriched charcoal — now commonly referred to as “bio-char”.

Charcoal is simply wood or other forms of organic matter that have been through a process of interrupted combustion. In short, it is partly burned, then retrieved ­before it turns into fine ash.

I collect my char from our stove or rake it up from the remains of pruning bonfires, the flames of which were quenched with water before the burnt plant matter was destroyed.

Charcoal contains no nutrients, but it is porous and has an ability to absorb and retain minerals and other nutrients. It can then make them available to plants, as needed.

Last autumn, a friend tried mixing pulverised charcoal into a compost heap so it would absorb most of the nutrients released by the decomposing organic matter.

He presented me with a large bucketful of this moist, jet-black, sweet-smelling bio-char.

I tried it by dropping a tight fistful beneath each of a dozen brassica, silverbeet and winter lettuce seedlings, plus some garlic cloves I planted in April last year.

The results have been almost unbelievable. I’ve never before grown such remarkably rich-green and healthy crops during winter. The flavour, too, was brilliant.

The garlic is now knee-high and I anticipate huge yields of superb, aromatic garlic in December.

The most amazing success, however, has been with winter-grown spinach.

I tried four varieties, each sown into rows 2m long with each row spaced 30cm apart.

Before sowing the spinach seeds, I created four shallow grooves in the soil and lined the base of each with composted biochar.

Germination was quick and drastic thinning of the overcrowded seedlings was necessary.

In late winter as the big leaves started to spread, I applied an extra-weak solution of fish emulsion and water. The result is about 4sq m of the most prolific, wall-to-wall spinach I’ve seen. The leaves were enormous and the flavour superb. We’ve been picking leaves non-stop for weeks and the plants are still sprouting.

I’ve even started to make my own, improved bio-char. It is so easy.

Lumps of charcoal are wetted and then pulverised with a heavy piece of wood so they are reduced to a mix of pea-size particles and black dust.

To a third of a bucket of this stuff, I pour in half a cup each of seaweed concentrate and fish emulsion. Also a good fistful of sulfate of potash. I even add a couple of teaspoons of boron (Borax from the supermarket is the same stuff) and a spoonful of Epsom’s salts (Magnesium sulfate). These extra minerals are great in sandy soils for growing beetroot, swedes and cauliflower.

To this is added the same amount of potting soil and enough water for a thick, black, slightly sloppy brew.

This can be poured over the soil and raked in or worked in before sowing pumpkin, zucchini, cucumber and sweet corn seeds.

It has proved great when a cupful is poured into holes before planting tomato or capsicum seedlings.

Bio-char is proving to be the greatest, most significant and beneficial revolution in organic growing techniques in half a century.

Used properly and wisely it could help resolve problems of world hunger by revitalising and permanently enriching impoverished soils.

It is the way of the future.

How to Properly Use Biochar

The novelty of bringing your own plants to life in your own garden is like no other. We see beauty in the art of gardening

We know a great garden, starts with great soil. At Nextchar, we are dedicated to helping make your garden flourish. Let our Nextchar biochar be the building block of your healthy soil.

Assess the situation

Figure out how much biochar you will need for your garden

Typically home gardeners use 5-10% biochar in the top 6 inches of their soil. However, you can see results from using just 2% biochar in your soil. Use our coverage calculator to calculate the exact amount to use.

Order your biochar here.

Charge it up!

Biochar compost blend

An essential step to properly using biochar is to charge your biochar with nutrients and microbiology. This means that you must mix biochar with fertilizer, usually compost, before applying it to your garden. Charging is required because of biochars ability to soak up nutrients and microbiology.

The most typical way is to mix your biochar with compost and let it sit for at least 10 days. A 50/50 mix of biochar and compost will work well for charging purposes. Most farmers mix 20% biochar in their compost blend and add the “compo-char” blend as necessary.

If you do not charge biochar before adding it to soil, the biochar will soak up the nutrients and microbiology from the soil, which can actually reduce the effectiveness of the soil.

Apply your biochar.

A few ways to apply biochar are top-dressing, tilling or hand mixing.

Top dressing – simply sprinkle your charged biochar on top of the soil and wet it. This is most effective if you layer the top of your soil with a compost and biochar mix.

It is also common for gardeners to build up their soil fertility over time by adding an 80% compost and 20% biochar mix to the top of their soil, as required.

Tilling – The conventional way to work soil amendments in is to use a tiller and mix it right into the soil

Hand Mix – If you are planting in pots, feel free to work the biochar around in your soil with your hands or a small rake.

Learn more about charging biochar in our white papers or feel free to contact us with more questions.

Biochar – what is it and how to use it

What is biochar and how is it made?

Biochar is a form of charcoal used to improve compost and top soil. It is created by heating wood in the absence of oxygen – the process is called ‘pyrolysis’. (This differs to a normal biomass boiler that ‘combusts wood’ – ie burns the wood with oxygen).

Biochar is a form of horticultural charcoal. However, the modern day biochar is formulated to a specific quality standard (eg UK-BBF, EU and IBC quality mandates). These standards not only require the biochar meets a specific chemical analysis, they often dictate that it is made in from sustainable resources using an environmentally ‘clean’ processes. Modern biochar retort kilns reduce the harmful emissions over traditional charcoal ‘ring’ kilns.

Why use biochar

Add biochar to soil and compost to improve:

  • Water retention
  • Nutrient supply to root
  • Decrease nutrient run of
  • Support microbes and AMF (mycorrhizal fungi)
  • Support the formation and stability of colloidal humus
  • Improve soil tilth

Environmental benefits include:

  • Carbon capture by locking carbon in soil for hundreds of years – offsetting your carbon foot print
  • Reduced NOx and methane soil emissions

Where to use biochar

  • Planters
  • Raised beds
  • Allotments
  • Lawns
  • General gardens
  • Add to compost* (see below)

How to apply biochar

The most powerful biochar benefits involve interactions with the root zone. It follows, the best place for biochar is in the root zone. Our recommendation is to dig it when planting (eg seed drills, tree holes or when cultivating soil. This is not always possible (nor desirable if following no-till regime!). Biochar benefits have been shown when used as a top dressing or when lightly hoed into top few cm soil.

How much biochar should I apply to soil?

Annual plants – biochar should be sprinkled onto the beds/containers then gently mixed with your soil/compost. (It is recommended the biochar used has been charged by passing through the composting process).

Perennial plants – 500g of char should be sprinkled into the planting hole alongside a mycorrhizal inoculant (eg Root Grow) before backfilling the hole with soil.

Which grade (size) of biochar should I use?

We recommend: 0-2mm fine granule for sandy soils and the 2-8 mm granule for all other soils

We do not recommend adding amorphous powder or large (>8mm) granules of biochar.

Our logic (supported by our testing) is as follows:

Biochar has three impacts on soil and microbes: chemical, physical and biological.

Chemical effects: biochar has beneficial chemical effects based on the surface chemistry of the sheets of carbon and the surface area of the carbon. These properties are determined by the raw material, time and temperature used to make the biochar. The actual granule size has a minuscule impact on the surface area – the active high surface comes from the sheets of carbon – see photo.

Many different raw materials (eg straw, coco, softwoods, hardwoods) are used to make biochars. Many will pyrolyse into amorphous carbon (tiny fragments of flat sheets of atoms (see photo). This amorphous carbon has a huge chemical surface area (ie micro pores <2 nm) but has no meso (2-50 nm) or macro (50-100 nm) pores. (See photo below) Activated carbon pellets also have high surface area but low mesopores and macropores. We can find no published papers or evidence that “activated carbons” which have been manufactured for many years have any benefit when added to soil. We infer from this that ‘high surface area chemical benefits’ are not paramount to biochars impact on soil. (If it was- we’d all be adding activated carbon to soil!)

There is a large and growing body of evidence that some biochars work in some circumstances – (ref Jeffery, biochar metadata analysis). The huge variety of biochars used in testing means it is proving difficult to establish exactly which biochars work.

Physical effects: biochars have physical interactions based on the size of particles. This can impact water flow (irrigation) and soil particle aggregation. Large particles will increase water flow and decrease aggregation. Fine particles will as a generalisation will be opposite. Hence on balance fine granules will be more beneficial in sandy soils, and medium granules will be better for heavy clay soils. The granule size also affects handling – granules are easier to handle and spread. Biochar powders and fine granules tend to be more susceptible to wind blow. (When using in the garden, we suggest a quick spray of water (via water-mist-sprayer) into the tub of granules).

Biological effects: biochars also have a biological impact on the root zone and soil microbes. The exact mechanism is still under debate. Our theory is as follows: microbes are small (5-100 nm), small enough to live in the mesopores(2-50 nm) and macro (>50 nm) pores formed in some biochars. The solid biochar pore walls act as a defence against being eaten by predators. The surface chemical structure of the biochar adsorbs nutrients. Normally once these sites are full of nutrients, the adsorption ceases. The microbes take up these trapped nutrients – releasing the sites to take up more. The microbes form symbiotic relationships with root hairs. They exchange nutrients (NPKs etc) for sugars. This symbiotic relationship is more viable when microbes have a safe home in biochar pores. We conclude this symbiotic biological impact from biochars is more important than the chemical or physical impact of biochar. (see photo below comparing amorphous powder with fine granules).

For the very best results, we conclude biochar should have the right pores present AND accessible to microbes for microbes to inhabit. Small fragments (<5nm) and amorphous powder do not have the right pores. Large granules (eg 25 mm) have many pores – but most are inaccessible to microbes). We believe the most advantageous size of biochars is small granules (0.1-2mm) with accessible pores of the right size. Hence we sieve and grind to produce a specific 0-2 mm grade of biochar. We believe we are unique at this point in time in preparing this grade.

We aim to combine the chemical functions of biochar with the biological functions. We only use the powder in our compost humification agent. We recommend the powder/fines for soil use, but we recognise many customers use and prefer the granules.

Can I add too much biochar?

Yes! Too many 2-8 mm particles will negatively affect aggregation and water holding and retention. Water will drain away too easily with too many large particles. We recommend a maximum 20% biochar (by volume) for heavy clayey soils, 10% for existing loams, and 5% for sandy soils. Please note – there are case studies illustrating biochar improves sandy soils. Biochar is a better growth media than sand as it holds water and nutrients better than sand. Adding biochar to sand often gives a better growth result. But – you would achieve an even better result by adding some sticky, water retentive colloidal humus to your sandy soil rather than just biochar.


Our biochar is made in the UK using wood from managed coppice woodland here in the North East of England. We supplement this wood with occasional deliveries of wood from tree surgeons (arboricultural arisings).


Our biochar will be tested according to the British Biochar Foundation (BBF) Quality Mandate. This is similar to the European Biochar Certificate. Why do we package by volume (litres) not weight (Kg)Biochar can vary in weight enormously due to water absorption. It is, therefore, more accurate to use volume.


Our goal is to supply the best value for money biochar in the UK. We offer a price match promise: if you buy biochar online from SoilFixer and find the same product delivered to a UK address at lower price we refund the difference or discount your next purchase to the difference. (Our promise is based on comparing the price per litre of each product. The price per Kg varies enormously due to biochar absorbing water and different supplies opting to supply material dry or damp).

How to use biochar – activation / charging it!

We recommend (along with most of the biochar scientific community) that you ‘inoculate’ (soak, charge, activate) your biochar with nutrients before adding it to soil.

If you prefer to buy activated biochar – please review our SF60 super compost product – it more than just activated biochar.

How do I activate / charge up my biochar ready for use?

We recommend you add it into your compost. Should I add my biochar direct to soil, mix with compost or add it into the composting process? From our test results, we believe it is better to add it into the compost heap. Biochar appears to bond with colloidal humus to create a bigger and more robust colloidal matrix. Biochar absorbs soluble nutrients and water.

Sources of biochar information

There are many excellent teams working on biochar such as the European and British Biochar organisations and Ithaka Institute. They have many links to scientific papers.

  • International Biochar Organisation
  • Ithaka Institute
  • British Biochar Foundation

Custom (bespoke) biochar formulations

The biochar industry is young with many research projects still underway looking at many different biochar formulations – everything from a super high surface area “activated carbon’ down to brown-char (partially burnt wood). Working with SoilFixer, we can offer a range of biochars:

  • Inoculate (charge) biochar with various items such as nitrates, urine, NKPs, trace minerals, rock dusk, AMF, specific root fungi (eg RootGrow™)
  • Mixtures of biochar with compost
  • Various crushed and sieved grades from 0-25mm (eg 2-8mm, <2mm)
  • Supply the biochar fresh and dry, or aged and wet

Energy recovery when making biochar

A core premise of biochar to be used as a soil additive (rather than charcoal) is hat biochar production is made in a sustainable environmentally non-polluting fashion. This means low (minimal) production of ‘smoky’ gases (VOC, CO, CH4, particulate matter (dark smoke), and that the heat produced during pyrolysis is recovered and used (rather than just going up the chimney stack).

Most approved biochars will, therefore, come from expensive ‘biochar pyrolysis’ equipment rather than from charcoal ring kilns. The kiln we use is a Kon-tiki. This is a low capital cost, small throughput unit that in the words of the Ithaka Institute can democratise biochar production worldwide allowing many small scale producers to make a positive impact. The Kon-tiki has been proven an exceptionally clean burn – it is, therefore, a huge step up from traditional charcoal production methods (clays and ring kilns). Our R&D Kon-tiki kiln does not have any heat recover, but when we move into our new premises our goal is to fit a heat recovery unit. On balance, Kon-tiki kilns have been approved for small scale biochar production.

Can I use activated carbon as biochar?

Activated carbon sometimes is known as powder activated carbon (PAC) or granular activated carbon GAC) can look like biochar. Can it be used instead of biochar?
Our primary goal is to improve crop growth. Based on our technical expertise many GAC/PAC simply do not confer the properties we believe essential to improve soil fertility. This does not mean you won’t get some chemical benefits (read all about activated carbon) and of course these forms of carbon are stable so sequest (lock) carbon. We believe you can get even more from proper biochar.

Can any biomass be used to make biochar?

Yes and no. Process conditions (time and temperature) and the starting biomass affect the final structure of the char produced. Our view is that only high lignin woody materials make highly beneficial biochar.The biochar we use is based on our research around understanding what compost is (and is not). How compost and colloidal humus affect soil and then how biochar and other powders affect humification.

We will be adding more information on biochar, colloidal humus, composting and soil additives to our FAQ and blog in due course so please register and come back to ready more soon.

Ever heard of biochar? For most home gardeners, chances are that it’s a brand new term.

In short, biochar is a charcoal compound added to soil that makes it more fertile. Biochar has a long and complex history of use in indigenous farming throughout West Africa and the Amazon rainforest where the incredible results can be seen even today.

Many scientists believe this ancient agricultural technique has the potential to increase crop yields and remove carbon dioxide from the atmosphere at the same time.

But what does any of this have to do with your home garden? You might not be running a high-yield farm or trying to capture carbon. But biochar has a host of benefits to the soil in your yard or garden and can increase your fertility significantly. If your home is built on infertile ground, trying to grow anything can be frustrating. Biochar can help revitalize poor soil and can help increase the harvest and yield in your vegetable garden.

What is Biochar, Anyway?

Biochar is technically a soil additive, or enhancer, that helps soil to create, sustain, and replenish the growing environment for plants and organic life to thrive within.

The name comes from its main component, charcoal and is the primary substance in biochar responsible for maintaining a versatile spectrum of other essential elements necessary for life. It is not the same as just charcoal though, so you can’t just empty the ashes from your fireplace and expect to improve your soil.

The word “biochar” takes “bio-” as in “biomass” and “char” as in “charcoal” and puts them together, because that’s actually what it is.

European settlers in South America called it terra preta de Indio, which is still a common name for biochar in Portuguese.

How biochar improves soil

Although making charcoal may sound like a strange way to boost crop production, the concept was proven more than 2,000 years ago, where pre-Columbian farmers in South America added charcoal to the poor soils of the Amazon rainforest to create a rich, fertile soil.

These soils improved with biochar from so long ago are still fertile today, and contain as much as 35 percent of their organic carbon in the form of charcoal. Research studies over the past decade at have found that these biochar enriched, charcoal-amended soils hold more water and nutrients while simultaneously making the water and nutrients readily available to plants.

The biochar itself used to improve the soil quality can be made from either wood or agricultural byproducts. The key is to heat the material to a high temperature in an oxygen-starved environment.

Indigenous farmers in pre-Columbian South America did that by burying the material in pits, where it burned for days. Today though, there are dozens of do-it-yourself videos on YouTube that teach how to make biochar in just a few hours using things like steel drums.

The soil fertility enhancing benefits of biochar are just one reason there’s a groundswell of interest in biochar production. Some enthusiasts are drawn by a desire to reduce atmospheric carbon dioxide. That’s because about half of the carbon from wood chips, corn stalks and other biomass — carbon that otherwise typically goes into the atmosphere — can be locked away inside biochar for thousands of years.

Most of biochar’s benefits are related to the extremely porous nature of the charcoal like material. Biochar is highly effective at retaining both water, and water soluble nutrients while also creating a healthy habitat for beneficial soil microorganisms.

Biochar can improve water quality, help the soil capture carbon for long periods of time, reduce nutrient and fertilizer leaching, reduce soil acidity, and even reduce the amount of water and fertilizer that required in the first place.

Multiple agricultural studies have shown positive effects using biochar to improve crop production in degraded and nutrient poor soils.

Biochar owes its characteristic rich, black color to the charcoal content. Historical studies show that it was originally made by adding a mixture of charcoal, bone, and manure to the otherwise relatively infertile Amazonian soil. The same method was independently discovered and used throughout West Africa as long as 700 years ago with similar results.

The charcoal portion of biochar is very stable and remains in the soil for thousands of years, binding and retaining minerals and nutrients, literally transforming poor quality soil into rich, fertile soil that retains its fertility over hundreds, or even thousands of years.

Deforested soils in the Amazon are typically productive for just a short period of time because of the poor fertility of the soil. This means that farmers must constantly move to new areas and cut down more of the Amazon forest to effectively grow crops, resulting in increasing deforestation.

Biochar “terra preta” soil, unlike unimproved Amazon soil, is less prone to nutrient leaching caused by heavy rains and floods because of the high concentration of charcoal, microbial life and organic matter. The charcoal holds, grabs and accumulates nutrients, minerals, and microorganisms.

Scientists estimate that some terra preta soils in South America created with biochar from the pre Columbian period were made by humans over between 450 BC and 950 AD. The dark, rich soil’s depth where biochar was made that long ago still reaches up to 2 meters deep even today.

Thousands of years after its original creation, this biochar enriched soil still regenerates itself at the rate of around 1 cm per year. It is highly sought out by local farmers in the Amazonian basin, who seek it for use in farming and also for sale as valuable potting soil.

This TEDx talk gives a short and very compelling overview of biochar.

According to the International Biochar Initiative, biochar is made through a process that converts “agricultural waste into a soil enhancer.” It can also be created from natural vegetation fires, such as those caused by lightning strikes, brush fires, and other conditions conducive to fires.

The Yale School of Forestry & Environmental Studies explains that biochar is created through a process called pyrolysis: “Organic waste such as wood chips, agricultural byproducts or switchgrass is burned, yielding oil, synthetic gas, and a solid residue resembling charcoal.” It’s a highly porous type of charcoal acting as a filter to absorb harmful chemicals and compounds while allowing helpful nutrients through.

Biochar has proven to be beneficial for a number of environmental concerns, including: supporting plant growth (and thus food security in developing countries), reducing soil erosion, diminishing the effects of deforestation, and preventing groundwater pollution by helping the soil to retain its nutrients. Furthermore, a number of studies have documented the use of biochar as instrumental in restoring forests and croplands ravaged by human consumption.

History of Biochar

Biochar is history’s best-kept agricultural secret to achieve incredibly fertile soil. Versions of biochar have been around for hundreds—maybe even thousands—of years in parts of Africa and the Amazon rainforest. In a time when the agricultural industry has sapped nutrients from the land, some parts of the world cannot produce adequate nutrition and climate change is an eminent threat, perhaps biochar will be necessary in the future.

Villagers in parts of West Africa have used charcoal and kitchen waste to replenish nutrient-poor soil and transform it into fertile farmland for approximately 700 years. West African women add ash, bone, and other organic matter to the soil in order to create what scientists call “African Dark Earths.”

One study out of the University of Sussex analyzed these methods and concluded that African Dark Earths, such as ash and bone, have the potential to improve soil fertility of soil in parts of the world that lack nutrient-rich soil and improve food security in a way that mitigates climate change. Potentially, the expansion of these ancient farming methods across Africa could stabilize regions affected by food insecurity.

On the other side of the world, Pre-Columbian Amazons used similar techniques. Scientists estimate that indigenous Brazilians have been using biochar, called terra preta de indio or Amazonian Dark Earths, for between 500 and 2,500 years.

At this point, scientists are not sure whether the biochar used in the Amazon was created intentionally or was naturally occurring within the environment. Whatever the case, biochar’s effects on fertility are astounding. According to Cornell University, fallow periods in Amazonian Dark Earths last only six months. By comparison, other areas in the region have fallow periods that last anywhere from eight to 10 years.

Unfortunately, widespread use of biochar in West Africa and the Amazon disappeared after European colonialism. It is likely that Western settlers favored their own farming practices and imposed these methods on their colonies, causing the use of biochar to disappear over time. Now these methods have been rediscovered.

What Science Says About Biochar

A study conducted by Rice University explored biochar’s uses for agricultural application and found that “when added to soil, the porous carbon has been shown to boost crop yields, lessen the need for fertilizer, and reduce pollutants by storing nitrogen that would otherwise be released to the atmosphere.”

What’s more, according to the International Biochar Initiative, “sustainable biochar practices can also produce oil and gas byproducts that can be used as fuel, providing clean, renewable energy.” The fact that this naturally occurring element can help to reduce our carbon footprint is pretty spectacular in itself.

“We know that biochar impacts the soil nitrogen cycle, and that’s how it reduces nitrous oxide,” explains Dr. Caroline Masiello, Rice professor of environmental and planetary science. Biochar is the result of a natural order of the life cycle process, of decomposition and reproduction, that when effectively applied can help repair our atmosphere by cleansing and removing excess CO2 from the air we breathe.

Scientists and green engineers believe that if we could harness this process and introduce more geoengineering into urban design and infrastructure models, such as rooftop gardens in cities vulnerable to pollution, there is a chance the effects of continued environmental pollution could be reduced, prevented, and perhaps even reversed.

Biochar stores carbon in a stable form, which prevents CO2 in the organic matter from dissipating into the atmosphere in the form of carbon dioxide gas. In fact, YaleEnvironment360 cited a study showing that 12 percent of global greenhouse gas emissions could be offset with biochar production. Biochar has even already been put forward as an option in reports by the United Nations Framework Convention on Climate Change.

Other studies have shown that the ancient Amazonians who used this technique produced similar results. This evidence fosters hope that the Earth is capable of replenishing and repairing itself. And if mankind does its part to help rather than hinder that process, we can help support the same natural protection mechanisms the planet has always had against today’s ever-looming threats of climate change.

Think of biochar as a giant sponge underground, trapping harmful runoff from pesticides, antibiotics, and other chemicals—preventing pollutants from reaching the aquifers that we tap into for drinking water. These aquifers also feed into rivers and lakes, making biochar even more important. Though it should be remembered though is this—the biochar of the past, from the Amazon, is vastly different in composition from today’s biochar.

Are There Disadvantages to Biochar?

It’s very clear that biochar improves soil and soil fertility, and also captures carbon at the same time. Are there any downsides to using it?

On a small scale, using it in our own gardens, probably not.

But on a larger scale, there are a few potential problems. The idea of burning millions of acres of crops and manure just to bury the remains and start the growing process again concerns some scientists and agriculture experts.

In an article posted by the Permaculture Institute in 2010, Dr. Mae-Wan Ho writes, “The biofuels ‘boom’ has already exacerbated climate change by speeding up deforestation and peatland destruction, loss of habitats and biodiversity, depletion of water and soil, and increased the use of agro-chemicals.”

However, Dave Levitan, writing for the YaleEnvironment360, explains this dual nature of biochar. Jim Hansen of NASA admits that while biochar “could absolutely add some benefit to a range of climate mitigation strategies,” it’s far from a “miracle cure.”

Despite the slow wheels of progress, there are already more than 120 companies already manufacture biochar or products related to it for farms and gardeners or sell pyrolysis equipment including pyrolysis cook stoves. “Most of the companies are located in the U.S., such as New England Biochar, although the number of companies involved continues to rise dramatically — including firms in Europe, Australia, and Brazil.”

Environmental Impact of Biochar

So is biochar an ancient miracle technique to end world hunger or a dangerous manmade additive with the potential to ruin the world’s agricultural industry? The answer is not a simple yes or no. It depends on the type of biochar and what it is used for.

In an article published by The Journal of Environmental Quality, the authors write that biochar is primarily beneficial to soils that are already low in nutrients. Adding biochar to soil that is already fertile will not necessarily help productivity.

In “Biochar, Carbon Accounting and Climate Change,” which appears in in the book Biochar for Environmental Management: Science, Technology and Implementation, the authors cite the Copenhagen Accord, which proposes to lower global temperatures by 2°C above preindustrial temperatures by converting biomass to biochar in order to meet this goal. Thus, biochar has the potential to positively impact the environment by removing carbon from the atmosphere and capturing it into the soil.

A lot of biochar’s benefits rest in its potential. Widespread use of biochar would be needed to see the kinds of crop yields and carbon sequestration that it’s capable of. However, biochar’s benefits are also dependent on the type of biochar used and how it is used. Additionally, more long-term studies are needed to ascertain if biochar would negatively impact soil environments or crop growth. Like most everything in life, biochar is not fully good or fully bad; it is dependent on how it is used and for what purpose.

Using Biochar in Your Garden

Why would you want to use biochar in your garden? Because biochar enriches the soil! Whether you’re growing flowering plants, fruit trees, vegetable gardens, or just a healthy lawn, the additive can improve crop yields by increasing water retention and moderating the pH of your soil. You don’t have to use biochar on a large scale to see its effects. You can see results when you use it to improve your own garden soil.

How to Integrate Biochar

To use biochar in your own garden, begin by mixing a combination of biochar and compost or fertilizer. Set this mixture aside for at least 10 days before applying it to your growing area, while continuing to blend and add water each day; when the mixture is ready to be applied, till it into the top four to six inches of existing soil.

How Much Does Your Garden Need?

According to Wakefield Biochar, for your average backyard garden with healthy soil, a 5-10-percent biochar mixture is ideal. That’s about one cubic foot for an eight-by-four-foot garden, or a one-gallon bag for a four-by-two-foot garden. If the soil doesn’t show adequate resupply of nutrients adjust the mixture accordingly, maybe starting by stepping up to 20 percent of the formula. However, if your soil is severely depleted of nutrients, begin with an increased proportion of half biochar and half compost.

Alternatively, you may choose to build up the soil fertility over time by repeating the process over the course of several months as needed. Keep in mind though, that it may take a few weeks to start noticing an improvement in your plant growth as a result of the increased nutrient absorption. However, an added benefit of using biochar is that its porous composition aids in water retention, so if your geography receives little rainfall, your biochar-enriched soil will help keep the garden better hydrated, and you won’t need to replenish the soil quite so often to sustain the nutrients.

Where to Get Biochar

The product is readily available for sale from a number of vendors, including NextChar, Wakefield Biochar, and even Amazon. A typical price for a one-gallon bag is about five to ten dollars, while a cubic foot will run about $30. However, you can also save money by making your own biochar. There are a few methods, but essentially, it involves starting a fire, tending it, and retaining the remains. Here’s the simplest way, according to

“Start by digging a trench in a bed. Then pile brush into the trench and light it. You want to have a fire that starts out hot, but is quickly slowed down by reducing the oxygen supply. Now watch the smoke; when it thins and turns grayish blue, dampen down the fire by covering it with about an inch of soil to reduce the air supply, and leave it to smolder. Once the organic matter has smoldered into charcoal chunks, use water to put out the fire.” Use the leftover charcoal for your biochar.

Another option is using reusable metal barrels like these for the fireplace, wood stove, or outdoor fire pit. Simply fill the barrel with kindling, such as wood chips, sticks and branches, scrap lumber, wood pellets, cardboard, nuts, bones, etc., and enjoy that warm, fuzzy feeling of sitting by a campfire—and saving the planet.

When building a fire to create your own biochar, always check with your local fire department to see if permits are necessary. The best weather conditions for the project are when it’s damp and windless. Thoroughly check your kindling for flammable substances, and carefully monitor the fire until it’s completely dead.

Biochar has a long and complicated history. From its ancient origins in West Africa and the Amazon rainforest to its modern uses in organic and green agriculture, biochar may be the natural soil additive the world needs.

In the home garden, biochar can be used help gardens grow in infertile soil or to get more fruits, veggies, and herbs out of the garden. Biochar can be a useful tool to save money and improve your garden soil to increase your harvest, while capturing carbon into the soil.

Nicholas Clowers is a freelance writer and editor for Russell Gibson Content. He is a Texan native and graduate of Texas Woman’s University, where he served as writing consultant for the English department. He is also a former actor, restaurant owner, Junior Olympic figure skating champion, and world traveler. He’s currently pursuing teacher certification for English and social studies. Nick is a voracious reader and passionate about writing on a variety of interests, including news, politics, education, science, and sports.

Saffyre Falkenberg began gardening with her grandmother as a child in Southern California. She continues to keep plants in her apartment in Texas and has a special love for succulents.

Learn More about Biochar

New England Biochar

Biochar International

Photo credits: Creative commons biochar photos courtesy of Engineering for Change, Matt Dil and Oregon Department of Forestry.

How to Make Biochar

For something that looks like a lump of charcoal, biochar certainly has a great press agent. The subject of books, articles, blog posts, research papers, workshop presentations, conference talks, and various top-ten-ideas-that-will-change-the-world lists. Its potential ability to address a variety of global challenges is indisputably large. So, how exactly do you make this strange material?

The following excerpt is from Burn by Albert Bates & Kathleen Draper. It has been adapted for the web.

Prefer audio?

Listen to the following excerpt from the audiobook of Burn.

This book describes many of the identities assumed by carbon but we linger most often upon what is now being referred to as biochar, a hard, almost crystalline form that persists long after most photosynthetic carbon has decayed away. Biochar may be added to soils with the intention to improve soil functions and to reduce emissions from biomass otherwise naturally degrading into greenhouse gases. Its formidable carbon sequestration properties can be measured and verified in a characterization scheme, or in a carbon emission offset protocol.

The term biochar appears more than seven hundred times in this book, although it only came into use at the end of the twentieth century after the discovery of charcoal-enhanced soils created by indigenous cultures dating back thousands of years. Scanning the research literature on biochar, now growing exponentially, it is clear the term has gone well beyond its original intent. It’s conventional wisdom in the biochar community that not all biochar is the same and not all char is biochar. Rather than attempting to standardize it, “fit for purpose” is the latest way of classifying different types of biochar.

We also know that people have been making and using charcoal since at least the time of cave wall paintings sixty-five thousand years ago. As recently as the early nineteenth century, professional charcoal makers, known as colliers, were common. Their job was dirty and dangerous, but necessary because charcoal was essential for heating, cooking, blacksmithing, and metallurgy.

The best charcoal was made at low temperatures. Fuel wood—often oak, hickory, ash, or maple—was generally stacked in piles and covered with damp earth, lit from the top of the pile, and left to combust and smolder for days. Burning wood slowly and at low temperatures is still one of the least expensive and easiest ways to make charcoal.

Biochar can be made from a much broader range of materials than charcoal can. Crop residues, manures, and wood are all potential feedstocks. In addition to use in the soil, newer uses for biochar are now competing with traditional uses for activated carbon, carbon black, and graphite. It is also well poised to displace, at least in part, noncarbon materials such as sand, Styrofoam, and fiberglass.

Tweaking the production parameters and the feedstock can result in widely divergent characteristics that allow biochars to be optimized or designed for specific uses. Perhaps the most defining characteristic of biochar versus many of its other carbon cousins is its planetary impact.

Unlike charcoal made from dwindling forests or activated carbon made from fossil fuels, biochar can have a tremendously positive effect on the planet both in reversing climate change and in providing products and services the world needs.

The specific thermal modification that converts biomass into biochar can be viewed from two closely related processes: pyrolysis and carbonization.

Pyrolysis relates to the chemical breakdowns that result in the liberation of pyrolytic gases. Carbonization is what comes next: the chemical buildup of the carbon atoms into solid structures. The bulk of pyrolysis and carbonization reactions occur in the temperature range from about 320°C to 800°C (608°F to 1472°F). One can think of pyrolysis and carbonization as simultaneous physical–chemical processes, changing the biomass into pyrolytic gases and charcoal.

We have occasionally found sources for perfectly good biochar already pyrolyzed and ready to micronize, moisten, mineralize, and microbialize. One biochar researcher we know uses her old aquarium filter charcoal to grow amazing tropical plants in pots.

In rural Tennessee we have managed to arrange delivery of truckloads of filtration char from distillers like Jack Daniels and George Dickel (produced in the town of Cascade Hollow). Of course, the whiskey residues, which are antifungal and antibacterial, can pose a problem for the compost pile or microbial inoculation, so we generally season this product outdoors and let rain denature the spirits.

When we first learned about biochar, we were convinced its ability to sequester carbon would make people sit up and take notice. That hasn’t happened yet for many different reasons. Later, we thought that its ability to improve yield and soil fertility was really what was going to cause people to sit up and take notice.

That hasn’t happened either.

Both of those ideas might still be approaching some kind of inflection point, but when or how the great turning might happen remains a mystery. Maybe if regulatory changes occur in carbon markets or if food security continues to be challenged by climate change, that will force a paradigm shift to regenerative agriculture. Or maybe there is something else that could drive such a change.

Recommended Reads

CARBON CASCADES: How to Restore Earth’s Natural Balance

Finding Hope in an Era of Climate Chaos

Why your soil needs biochar (plus two ways to make it)

This special type of charcoal made from waste wood will enrich your soil and help save the planet.

Words: Sharon Stevens Images: Phil Stevens, Sharon Stevens

Walk into a garden centre, and you can buy a bag of biochar. It’s even possible to order biochar by the tonne and apply it to pasture, usually mixed with an organic fertiliser. The only problem is most biochar is imported from China.

Adding biochar to your garden and pasture is an organic way to improve the soil. Research has found properly-made biochar helps the soil by:

• holding moisture;
• retaining nutrients like nitrogen, phosphorus, and potassium;
• raising the pH of acidic soil;
• reducing the incidence of plant disease;
• increasing plant productivity;
• limiting the bioavailability of heavy metals;
• reducing nutrient leaching.

Then there is biochar’s potential to help with climate change. Biochar can:

• store carbon over hundreds of years (sequestration);
• reduce greenhouse gases methane (CH₄), and carbon dioxide (CO₂) generated during waste disposal, waste processing, and recycling;
• produce renewable energy.

Another bonus is it’s made from agricultural waste, like tree prunings, nut shells, maize stalks, bamboo, and woody weeds. This is commonly burnt or left to decompose, releasing carbon into the air.

Turning it into biochar creates a valuable asset in your soil, and holds carbon in an inert state, instead of releasing it into the atmosphere.


Biochar is a fine-grained, highly porous kind of charcoal. It is made using pyrolysis, a burning method that ‘cooks’ the wood without using oxygen, producing solids (biochar), liquid (bio-oil), and gas (syngas).

This is different from the charcoal you’ll see in a fireplace, where wood combusts (thanks to oxygen), producing heat, light, ashes, gases, and smoke.

Research shows it has other valuable benefits:
• when biochar is mixed into animal manure, compost, urine, or other nutrient-rich organic waste materials, it only takes a few minutes to reduce noxious odours. This indicates nutrient losses (mostly nitrogen, which is released as ammonia gas) from these substrates is at least partially inhibited, very quickly;
• biochar literally soaks up nitrates, phosphates, dissolved organic carbon (DOC), and other easily soluble substances during aerobic composting;

Scientists believe biochar used in agriculture will play a big part in organic nutrient capture and recycling. For example, biochar could be used in manure management systems to decrease nutrient losses, reduce odours, and to improve organic fertiliser efficiency when applied to the soil. It will also reduce greenhouse gas (GHG) emissions during the process.


Making good biochar can be as easy as adding a tin of wood to your winter fire. Phil Stevens shares his tips for making your own biochar, and how to use it in your garden.

Phil Stevens has spent many years working to combat climate change.

“It’s soul-destroying to see the effects first-hand,” he says. “The biodiversity loss and social disruption. I wanted to
take action.”

Phil now works part-time as an energy and carbon consultant to businesses wanting to reduce their ecological footprint. He volunteers with transformation-oriented community groups.

At home, he has planted hundreds of trees. He’s continually looking for new ways to reduce his family’s emissions from transport, direct energy use, and material consumption.

But he wanted to do more.

“The answer was beneath my feet, getting more carbon into the soil and keeping it there.”

His first step was to adopt no-dig gardening and no-till cropping. These methods minimise carbon release while preserving soil structure, helping plants expand their root zones, and storing carbon.

Seven years ago, he began experimenting with simple, inexpensive ways to make biochar. It involves cooking the ‘biomass’, usually waste-wood material, using a special burning process called pyrolysis.

To use biochar in your garden, it’s best to ‘pre-charge’ it with microbial lifeforms. If you add biochar straight into your soil, without ‘charging’ it, soil micro-organisms can migrate into the highly porous char, reducing crop yields for several months, up to a year.

Eventually, micro-organism populations will increase and migrate out again, re-charging your soil. To avoid this delay, you can ‘pre-charge’ biochar with microbial organisms.

Step 1: Choose your biomass

The best ingredients (or feedstock, as biochar enthusiasts call it) to turn into biochar is woody material (biomass), already on your block or close by. This is material that would otherwise be left to decompose, or burnt.

Phil makes biochar from slash from firewood trees, nut shells, coppiced new-growth willow, pruned branches, wood chip, corn cobs, and woody weeds. Overseas, biochar experts are experimenting with animal manure, often mixed with sawdust or wood chips (to help dry the manure).

Phil’s tips:
• use fast-growing woody plants which rapidly sequester atmospheric carbon while growing – converting them into biochar keeps carbon in a stable form;
• avoid fuels that release toxins, such as treated timber, rubbish, and bleached paper;
• dry biomass completely before cooking.

Step 2: Cook your biochar


What you need: tin cans/roasting pans, wood burner/fireplace

Phil’s favourite approach for small batches needs no special equipment. All you need is a fire-worthy container and a clean-burning wood fire (with adequate airflow).

Fill the containers with biomass and place in the fire as it dies down overnight. In the morning, it will be biochar.


Phil made his first containers from matching soup tins. He used needlenose pliers to ‘crimp’ the open end of one tin so that it would fit into the open end of another. Once joined, the tins formed a tall, closed cylinder that opens in the middle.

But after about a dozen trips through a hot fire, the cans rusted so much they developed holes.

He now uses two stainless steel steam-roasting dishes (176mm × 108mm × 65mm). These tolerate much higher temperatures, and are robust enough to use for a second winter. The lids also fit better than the soup tins, limiting gas exchange, for a higher-quality char.

“It’s just like adding another log to the fire,” says Phil. “In winter, we use our wood burner daily for home heating and stove-top cooking. By spring, (the amount of biochar) really adds up.”


1. build up a good bed of coals;

2. make sure the fire is burning hot;

3. pack containers with biomass – make sure the containers close properly but don’t seal them as gases must be able to escape;

4. place filled containers directly on top of coals, then shut the fire door, but make sure there’s a good draft – if the wood burner has a glass door, you’ll be able to see the pyrolysis taking place as flames come out from under the lid;

5. allow the fire to burn down overnight;

6. remove the containers the next morning, once the biochar is fully cooled – if the containers are opened when the char is hot, the inwards rush of oxygen may start a fire.


Phil recently wanted to make a larger batch of biochar quickly, using a mound of subsoil left behind after a pond excavation. He and a friend dug out the top to make a cone shape, creating what looked like a mini-volcano.

How a cone pit works

A well-built cone fire burns hottest in the centre, driving a rolling air flow. Gases released during the burn rise along the sides of the cone, then fall back towards the centre of the flames where they re-burn. This ensures a clean fire.

Over time, a bed of coals builds up in the cone’s bottom. In a hot fire, very little oxygen penetrates this bed. Heat continues to drive off all the volatile components, leaving carbon behind as biochar.

“A balanced burn takes practice,” says Phil. “Continually adding more biomass prevents the top coals turning to ash. Adding too much, too quickly, lowers the fire temperature, creating smoke.”

If the biomass is not sufficiently hot for long enough, it won’t pyrolyse completely.

“It’s best to use smaller ‘feedstock’, especially when it’s almost time to douse the fire.”


1. Build your cone in a sheltered spot, from soil containing minimal organic matter. Topsoil must be lined with a good layer of subsoil, or it may catch fire.

2. Dig a cone with a minimum diameter of 80cm at the top and a minimum depth of 55cm in the centre. A small or narrow and
deep cone will cool too quickly through its earthen walls. If in doubt, always go wider.3. Make your cone’s sides as regular as possible for smooth airflow.

Phil uses small ‘feedstock’ like branches removed while pruning, which is easier to manage, especially when it’s time to put the fire out. These are up to 5cm in diameter.

3. Choose a calm burn day. There will be smoke if the wind blows away evolved gases before they pass through the entire fire column.

4. Start the fire with a tower of twigs and fine kindling. Leave plenty of air gaps. At the top, build a tinder ‘bird’s nest’ using dry leaves, very fine twigs, and palm fronds. Add a bit more kindling on top. Light the tinder. The fire will burn down the tower to create the initial bed of coals.

5. Add kindling, then gradually add larger material as the coal bed develops. Phil’s cone can handle branches up to 5cm diameter.

6. Burn until the cone is full, although you can stop earlier if you run out of feedstock.

7. Douse the pit with water as soon as the flames die down. This prevents the top layer from turning to ash, and steam will open pores in the biochar. After a few burns using this pit, Phil inserted a 25mm galvanised steel pipe at the bottom of the cone to drain off and save the ‘quench’ water.

8. Alternatively, cover the pit with dirt when the burn is complete, then wait until the following day to unearth the finished product.


Biochar is a durable form of carbon that changes very little in the presence of chemical and biological activity (recalcitrance). Ages for black carbon in some grassland soils have been reliably pegged to more than 7000 years in the US-Midwest, and more than 12,000 years in Russia.

Scientists have found areas of the Amazon where soil up to 2m deep has high concentrations of charcoal and organic matter.

These dark-coloured soils – known as ‘terra preta’ (dark earth) – are highly fertile and have supported agriculture for centuries.

Analysis of the soil has found it’s made up of burnt plant and animal remains, manure, bones, and fish. The soil also has good nutrient retention and a neutral pH in areas where it’s generally acidic.

These soils are only found in populated areas, suggesting humans are responsible.

Sources:; The basics of biochar,


Step 1Step 2Step 3Step 4

Who: Phil Stevens
Where: Ashhurst, 15km north-east of Palmerston North
Land: 1ha (2.5 acres)

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This article first appeared in NZ Lifestyle Block Magazine. Discuss This Article

How to make your own biochar

I’ve spent a considerable time both researching and experimenting to find a good way to make biochar. My main conclusion is that there are many many bad ways shown on the internet to make biochar and the main problems are:

  • the method produces pollution (excessive smoke)
  • the method relies on inefficient combustion
  • excessive fuel is used to produce biochar with low yields
  • methods are time consuming – typically 2 or 3 hours for one small batch
  • the equipment is excessively technical or over engineered
  • they burn high quality firewood which would be better used to heat a home

Learn more about the benefits of biochar

I concluded that I wanted a fast method, that could burn green freshly cut branches from hedge trimming and scrub clearning in the garden. It needed to be simple and not produce excessive smoke. It also needed to be able to deal with relatively large quantities at once. I wasn’t concerned about getting the maximum possible weight of biochar from the waste material burnt, instead I sacrificed a small amount of yield for ease of operation and clean burning.

How to make biochar

The “top-down” fast furnace way

The counter-intuitive method I settled on basically consists of filling a drum with close packed branches and twigs. The drum has an open top and bottom and is supported a few inches off the ground by three sturdy blocks of wood. The drum itself has large air holes cut into it two thirds of the way up the side – mine are triangular, but only because that was easiest to cut with the jig saw at the time.

Once the drum is stacked to the top dry newspaper and kindling is placed across the TOP of the drum and lit.

This dry kindling must spread across the whole top and be sufficient quantity to get the fire established across the width of the drum quickly – this is important to prevent smoke while you make biochar

I haven’t seen anything quite like this anywhere on the internet and I can vouch for its effectiveness – I’ve done about 10 loads in the past few months and will use it to make biochar through the winter too.

The newspaper and kindling is lit and flame spreads rapidly across the drum. The heat from the fire cooks the wood beneath which pyrolyses and gives off smoke. This smoke rises through the very hottest part of the fire where it breaks down into very simple ‘clean’ syngas (mostly hydrogen and carbon monoxide). Once this gas rises above the hottest part of the fire it combusts with oxygen from the surrounding air above the top of the drum.

Within ten minutes the flames will have descended all the way to the bottom of the drum and within around 20 minutes of being lit the flames will die down substantially. At this point the wood has essentially finished charring and you are ready to put the fire out and collect your fresh homemade biochar.

To do this I tend to douse the whole thing with some water from a hosepipe then, wearing a big heavy fireproof glove, I drag the drum away from the remaining pile of biochar. Spray a bit more water to cool the whole area down then simply shovel the char into a big container of water to stop it burning further.

At this point you could spread your wet biochar onto the soil, however I prefer to spend a few minutes breaking up the larger bits first and then compost it with my normal garden waste. Then when you spread the compost on the garden the biochar is already mixed in with it and has had a chance to absorb nutrients and allow fungi and bacteria to get established – a real bonus for developing healthy soil.

Issues and possible future improvements

Currently I don’t have anyway to measure my yields so I can’t say for certain what mass of carbon I’m getting out per load. Unfortunately adding water to the char messes with any yield calculations based on mass. My gut feeling is that it is a ‘worthwhile’ amount and it certainly gets rid of garden waste quickly (and spectacularly!!!).

To get through lots of waste I would like to have a second one made up exactly the same way – then you could be loading one while the other burns out and get through twice as much in the time.

Power user tips

When loading try to put smaller diameter sticks at the bottom and larger at the top – the higher they are in the barrel the more time they get to char completely

  • Keep some extra kindling on hand when lighting – the only time I have ever had problem with smoke (and it was black and nasty for five minutes or so) was when I had been stingy with the kindling at the start. Some of the smoke was going past (rather than through) the hottest part and so didn’t burn completely.

  • If you are getting small amounts of suitable fuel over a period of time you can load it into the drum as-and-when you collect it and then light it when ever it gets full enough.
  • Don’t try adding extra fuel to the top – you are just likely to make it smoke – save it for the next load instead.
  • This gets seriously, seriously, seriously hot. Make sure you have plenty of clear space around and over head and some water on hand. I’ve had flames 20 foot high and the area has been so hot that we retreated back about 10m from it – I guess that is the cost of burning stuff fast. Don’t attempt this on a windy day, or “fire-risk” day.

After you first make biochar for your own garden I’m sure you will see both many more ways to produce it, as well as many possible fuels to use. I’d love to hear about any successful (or even unsuccessful!) experiments.

Do you have a personal biochar making story to share?

We are looking for many more personal stories of your successes (and failures!) making biochar. Whether you are making 100 tonnes a week or a have an occasional burn in your backyard, let us know.

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We are constantly asked the question, “How much biochar should I use?” It’s a great question and the answer isn’t always obvious. From everything we have seen in our own use and through the biochar research of others a good “rule of thumb” is 10% of the planting area should be biochar. If your soil is absolutely horrible you should probably start with a 50/50 mix of biochar and compost and apply about 1/4 lb per square foot. Really bad soil needs a big injection of organic material along with the biochar. Of course, just to keep things moving along we’ve asked for another research project to be conducted at the University of Missouri to take a look at two kinds of plants — radishes and grass. We chose radishes because anecdotal evidence suggests vegetables that grow underground tend to see less improvement in growing than vegetables that grow above ground – tomatoes tend to do very well. Grass was selected because it is such a great opportunity for every parent that has to deal with their lawn most of the year to give them a healthier field of grass that has fewer weeds and stronger root system that is drought resistant. So, we begin our journey with the Mizzou crew of researchers, Jeff and Dakota. Here is a summary of what they are going to do for us…


Biochar has been around for centuries, but a relatively new agricultural carbon product that is making its way into the hands of the people with help from companies, such as Wakefield. The end product with the right ratio of soil, compost and biochar can produce a re-energized garden or lawn by contributing to healthier soil that produces better yields, help with drought-resistance, soil that lasts much longer than in previous conditions, and is also considered carbon negative. Proposed Plan: Dakota and Jeff have set up an experiment with Wakefield biochar to test optimal ratios of biochar, compost, and soil to determine how much actual biochar should be used for the consumer buying the product to use in their garden or landscaping. The two current variables we are testing are the different percentages of biochar and compost that we are adding to a 50% soil. Through research, we have discovered that usual biochar products have used 10-20% biochar to their mix and have shown great results. We are testing within that range and a little less (5-8%), as we are also testing the proper amount of water to be added to the ratios of the mix we created to further our results to see what best use Wakefield can have with their biochar. There are also two controls, possibly three, as one control will be 100% soil and the other 100% compost. Our third possible control would be a 50/50 split of compost and soil for further data analysis. Dakota and I are currently waiting a week to allow for the biochar enough time to activate, as Wakefield biochar is 97% carbon and much like a Brita filter in your fridge you must wait for the carbon to activate to help with porosity. Carbon in biochar if not allowed time to activate can result in a lack of growth to new seeds or plants already planted around the biochar. Biochar acts as a magnet when mixed with soil that pulls and keeps the soil’s nutrients, which keeps the nutrients from leaching out from watering, weathering, planting, etc. In the picture below you can see we have completed the mixing process with all the mixes labeled with the ratios we proposed and are now in the process of waiting for the carbon to activate, so we can plant our radish seeds that we will be using throughout the experiment. We choose radishes because they are a plant that grows underground and one of the things we wanted to find out is if plants that grow underground will be negatively or positively affected by the different biochar ratios.


Our main goal in completing a semester of data collecting and research is to become clear on the proper application rate of biochar so that we can easily explain it to Wakefield’s customers. Being able to inform the average person about Wakefield and what they have to offer is extremely important in getting their name out there as a leader in biochar products. Dakota and I will take our data collected and accurately see what the best ratio of biochar to add to the mix of compost and soil so that Wakefield can produce an efficient product that is fair to the buyer and will show the best results.

How to Use Biochar: Where It Should and Should Not Be Placed

There’s no doubt biochar can benefit many different types of soil. Due to its high adsorption and nutrient holding capacity, biochar can prevent both water and nutrients from leaching while still allowing them to be readily available to plants. These properties, which can significantly improve your soil’s fertility, also make biochar useful in reducing water erosion and fertilizer runoff.

Still, you may be wondering how exactly you should use and store biochar for your specific application. The answer depends on a few things, like how fertile your soil is before applying biochar, or whether you intend to use biochar to grow crops.

Using biochar in near-term applications

Charging up your soil with biochar

In the rare case that your soil is already very fertile, biochar can be directly added to the soil. Biochar, however, brings the most benefits to soil when it is “charged” or inoculated with nutrients and soil microorganisms to help prime your soil for improved fertility.

Though many different methods for charging biochar exist, most procedures follow several basic principles, which include:

  • Containing enough moisture for nutrients to dissolve and adsorb to the pores of the biochar
  • Introducing a wide variety of nutrients
  • Inoculating soil-borne microbes through compost or other methods
  • Letting the charge progress at least 14 days, to allow beneficial soil biology to inoculate

Charging should be tailored to your situation. For most near-term applications, it is best to blend the biochar with a high-quality compost containing the biology that would most benefit your plants.

If you are not sure about the quality of your compost, you can try one of CharGrow’s proprietary products, BioChar Source™ or BioGranules™. Both are charged, or inoculated, biochar that have already been loaded with beneficial microbiology and microbial food and have proven growing results. Field trials on growing media and soils in the United States have demonstrated that BioGranules enhances biological activity and plant performance when it is added at 2 to 3 percent by volume in growing mixes or 15 to 20 pounds per acre in row crops.

Incorporating biochar and compost into your soil

Compost can be mixed with biochar before being added to the soil or it can be worked into the field when it is being applied. In the latter case, the biochar would be laid on top of the soil first, then the compost, before they are mixed into the soil through tilling or other methods. The ratio between compost and biochar can be as high as 1:1 and the biochar is left to inoculate for at least a couple of weeks.

In some cases, the biochar and compost are partially mixed while they are being transported to a field. Here, biochar and compost is loaded into a truck in alternating layers before it travels to the field.

Alternatives to compost inoculation

Biochar can be mixed into a field intended for cover crops. Cover crops are plants that are grown to improve soil health and other aspects of soil for the crop that will follow (for example alfalfa that is grown prior to planting sweet corn). After mixing in biochar, the native microorganisms already present in the field move into the biochar over several months. This method of charging has been especially successful when the cover crops are nitrogen-fixing legumes such as clover.

Biochar can also be charged with other materials such as liquid fertilizer

The best place to put biochar

The best location for biochar depends on your application.

If biochar is used as a soil amendment, you should work the biochar into the plant’s root zone – the part of the soil surrounding a plant’s roots – incorporating the biochar into 4 to 6 inches of soil depth if possible. This way, you will make full use of biochar’s remarkable capability to hold water, retain nutrients, and host beneficial soil biology. Working the biochar into the soil also minimizes the chance that the biochar will be disturbed, dried out, or blown away.

If biochar is used to purify storm water, filter contaminants, or reduce erosion, you do not necessarily need to work biochar into the soil. In these situations, biochar is used in locations that are optimal for the specific needs of the project and often placed within containers specialized for each use case, such as landscape socks and filtration systems. For example, you can place the biochar where water is running off land, roofs, roads, or other contaminated sites – including those that are aboveground.

Best management practices when applying and storing biochar

Most biochar products have fine, dust-like particles that can be swept away by wind or water if proper precautions are not taken.


The best way to prevent your biochar from being lost to wind is to moisten it. This helps weigh down the biochar dust and is the reason why CharGrow’s BioChar Prime™ product is pre-moistened prior to shipping (though customer moisture specs can be accommodated).

Whether or not you moisten the biochar yourself, you should always consider its moisture content when determining your application rate, as you may over- or underestimate the amount of biochar you require for your situation. You should always apply biochar in the right weather conditions and when winds are mild.


Water can sweep biochar away, especially at sites with steep slopes or high rainfall. To prevent your biochar from being lost to water, you should properly incorporate the biochar into the soil or apply biochar with wetter materials such as compost or mulch, depending on the types of plants you are growing.

How to Charge Biochar

When I was growing up on a small farm in Virginia we used untreated biochar on struggling soils, though we didn’t call it biochar then. I was told that it should only be used on weak soil that we weren’t using for cash crops in the next year or two. We’d plow it in after harvest, and the next spring I watched as the weeds and wild annuals that pioneered that land came up anemic, stunted and off-color. Given a year or two fallow, the biochar resulted in strong improvements in crop health and yield when we finally did replant it.

We now know that biochar without inoculation is like a sponge that absorbs soil nutrients until it develops equilibrium with the soil. Only then is its promise realized. But lying fallow for two years isn’t needed – if you inoculate biochar ahead of applying it, your soil will improve almost immediately.

Biocharging (inoculating) the biochar is simple and easy. Doing so actively accelerates soil recovery and the associated microbiology. For example, a 2014 study published in Soil Biology & Biochemistry1 shows that biocharging greatly accelerates growth of mycorrhizae, which penetrate plant root cells and improve uptake of soil nutrients including nitrogen and, in particular, phosphorus – which can typically be difficult to retain in soil. In the study, they determine that inoculating the biochar results in three times the growth of mycorrhizae than in untreated biochar. Similar studies have been done for other microbiology.

This may sound complicated but, rest assured, just about anyone can easily make biochar at home (or buy it), and inoculating it doesn’t have to require any more equipment than a shovel or pitchfork.

Make or buy biochar?

Making biochar is a relatively simple process. Wood or other biomass is burned in a low-oxygen environment causing pyrolysis, changing its chemical and physical composition. The end result is a nearly-pure carbon material that will last in your soil almost forever.

According to Michael Low of Green Fire Farm2 in Vermont, “The easiest method with common materials is the T-LUD stove … These usually employ a 55 gallon (210 litre) drum and some variety of hardware for drafting and gas flow.” His favorite design is the Hookway Retort,3 which is simple and easily built with local materials, but many designs have been published. YouTube is a goldmine for additional ideas on producing biochar.4

Many people purchase commercially-produced biochar such as that made by the craftsmen at Vermont Biochar,5 for several reasons. First, because they use more advanced tools and techniques than the home producer can easily acquire, commercially-produced biochar is usually more consistent in composition and charred under ideal temperatures.

Second, they are able to produce inoculant tailored to specific uses. Vermont Biochar, for example, produces (by hand) several versions ideally suited for either leafy annuals, root crops, or shrub or woody perennials. Each uses a different composition of inoculant to tailor it for the specific application.

If you can make biochar* on your property however, it’s probably best you learn how, and to stack functions of your waste residue in keeping with permaculture principles. What biomass you make your biochar with is far less important than how you biocharge it.

Biocharging biochar

Even commercial biochar producers say their products benefit from being biocharged again once it’s on your property, to tailor it to your site conditions. Here are two easy methods you can do at home.

Compost charging

The simplest and most efficient method to biocharge your biochar is to simply mix it into your compost piles, stacking functions to benefit both the biochar and your compost. Even if you buy inoculated biochar, rather than producing it on-site, it will be improved by maturing in your compost. You can use as much biochar as you want, up to about an even 1:1 ratio with the compost, so don’t worry too much about overdoing it.

Thayer Tomlinson of the International Biochar Initiative,6 seeking to foster economically viable biochar systems that will safely enhance soil fertility and function, emphasizes the value of inoculating biochar in the compost pile:7 “For the biochar material itself, undergoing composting helps to charge the biochar with nutrients, without breaking down the biochar substance in the process.” Better still, there are benefits for the composting process, which “may include shorter compost times; reduced rates of GHG emissions; reduced ammonia losses; the ability to serve as a bulking agent for compost; and reduced odor.”

If you use the compost method to biocharge, some experts also recommend adding both manure and bones (preferably broken up first, but not necessary) to your compost pile. In the Amazon, they used biochar, manure and bones to make Terra preta8 – and it remains extremely healthy soil to this day.

Quick tip: If you have time, a great way to get the most out of your biochar is to spread it an inch thick or less into your farm animal bedding. Then, when the bedding is spent, add it to the compost pile. The biochar is essentially ‘double-charged’ in this way. Also, in addition to stacking functions of your animal bedding, this can help reduce odors. Anecdotal evidence suggests it can also reduce illness among your animals!

Rapid charging

The other way to inoculate your biochar is a bit more labor-intensive, but you can complete the process in hours or days, not months. First, fill a 55 gallon (210 litre) drum with fresh water and biochar. If you are using municipal treated water, let it sit for a couple days to remove any chlorine. Then add compost tea or worm castings and leachate to the barrel with some soil from the area where you will use the finished biochar. For example, if you are going to apply the biochar to your fruit orchard, add some soil from around a robust and healthy tree in that orchard. This will help charge the biochar with the ideal microbiology for your specific orchard.

Once everything is well mixed, insert a long tube such as a length of PVC pipe into the barrel and direct air from a blower into the tube, or use a pond aerator and air stones. Aeration supercharges the inoculant and gives the beneficial microbes a massive head start, and helps them adhere to the biochar. Continue this for 12-24 hours.

Applying the biochar

Once your chosen procedure is complete, your biochar is properly biocharged and ready for you to apply it to the area you’ve selected. You can repeat this process annually, although it might be better to apply biochar to new areas with each batch so that as much soil as possible is amended.

There are two primary ways to effectively apply biochar:

Tilling Application

Spread pure inoculated biochar about a ¼in (6mm) thick on the soil before normal tilling. Do this at the same time you till in your other soil amendments. It’s that simple. For larger areas such as pastures, the ideal amount of biochar to till or disc in is one ton per acre, but if you don’t have that much, spread out what you have and add more each time you amend the soil.

No-Till Application

You can spread pure inoculated biochar around a grow area, then mulch as normal to hold the biochar in place. It takes about 10 pounds (4.5kg) of biochar to properly cover 100 square feet (9.3m2). For potted plants, use pure biochar at a ratio of about 1:16 with your potting soil – about ½ cup per gallon of soil (118ml per 4 litres of soil). This ratio is good for raised beds as well, one gallon (4 litres) of biochar per 16 gallons (64 litres) of soil.

In all cases, till or no-till, if you inoculated biochar in compost (at ratios up to 1:1, remember), just apply compost as normal – the presence of biochar doesn’t change the amount of compost used.


Highly flammable gases are released during pyrolysis, so make it outside, well away from buildings, animals and people!

1 A mycorrhizal fungus grows on biochar and captures phosphorus from its surfaces, Soil Biology and Biochemistry, Volume 77, October 2014, pp.252-260
7 The use of biochar in composting, Marta Camps, Massey University; and Thayer Tomlinson, International Biochar Initiative, February 2015

Further resources

Biochar: how to build soil, lock up carbon and build fertility on the farm

Building soil with biochar PM79

Biochar stoves PM78

Plus read: What is charcoal and how can biochar help mitigate climate change?


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Charcoal May Help Improve Soil Quality


This is Talk of the Nation Science Friday. I am Ira Flatow. A bit later in the hour, we’ll be talking about open access to biomedical research and children and sleep. But up first, poor quality soil. It’s a problem for farmers around the world. Dirt stripped of nutrients by years of over-farming and chemical fertilizers. Well, this week there’s new evidence that an old farming practice traced back at least 1,500 years to tribes in the Amazon basin can give new life to nutrient-poor dirt. It’s called “black gold agriculture.” The idea is really simple. You add charcoal from burned organic matter to the soil and the dirt holds on to nutrients and produces lots more crops.

This week, scientists at the American Chemical Society meeting presented the results of a controlled study of black gold agriculture. And they found that fertilizing with charcoal produced more crops and captured carbon from the air, right out of the CO2. So the practice could also combat global warming. Sounds too simple, too good to be true? We’re going to talk about it. Our number is 1-800-989-8255. 1-800-989-TALK. Mingxin Guo is an assistant professor in the Agriculture and Natural Resources Department at Delaware State University in Dover. He joins us today by phone from his office. Welcome to the program.

Dr. MINGXIN GUO (Assistant Professor of Agriculture and Natural Resources at Delaware State University): Hi.

FLATOW: How do I pronounce your name?

Dr. GUO: Mingxin Guo.


(Soundbite of laughter)

FLATOW: I’m sure I’m not the first one who’s had some trouble with it, but thank you for pronouncing it for me. Let’s talk about poor quality soil, a big problem around the world. Why is that?

Dr. GUO: Yes. So deterioration and chemical degradation is a severe and worldwide problem. It is expressed as soil compaction, poor tubes, surface crafting(ph), slow water seepage, low water draining, low nutrients and a low nutrient retaining, and also decreasing crop productivity. This problem is mainly caused by long-term chemical fertilizer application and mechanical tillage. The level of organic matter determines the quality of our soil. All the soils have high organic matter content, say, six to 15 percent. But soil plowing makes the organic matter decompose quickly, while chemical fertilization doesn’t incur any external organic matter adhesion. So year after year, farmland soils become low in organic matter and the quality turns poor. So currently, most of farmland soils have organic matter content lower than three percent.

FLATOW: Ah. So what does adding charcoal to the soil, why does it make it a better fertilizer?

Dr. GUO: Charcoal is a fine-grained, porous black carbon, and it is generated from plant materials. And it is non-toxic to plants. So there are many tiny pores in charcoal. So once applied to soil, the pores will allow air to diffuse into the soil. Plant roots need the air to breathe. And in the meanwhile, the tiny pores will hold water and nutrients and later supply it to plants. More important, unlike other organic fertilizers, charcoal is very stable and it will not decompose to carbon dioxide. So once applied, it will stay in soil for hundreds to thousands of years. So to summarize, the high stability and porosity make charcoal a better fertilizer than other organic materials.

FLATOW: And you’ve actually conducted tests showing this?

Dr. GUO: Yes.

FLATOW: Wow. Well, that’s good. Our number, 1-800-989-8255. Let’s go to Bob in Cleveland. Hi, Bob.

BOB (Caller): Hi. Hey, how you doing? I have a question. If I wanted to do this in my backyard where I have a garden, could I just buy a bag of, you know, like charcoal that they use, you know, when they barbeque something and add it to the soil? And, you know, what kind of quantity would I add?

FLATOW: Or what about the ash that’s left over, too? That’s a good question. Dr. Guo, could he just buy a bag of charcoal and…

Dr. GUO: Theoretically, you can buy some charcoal directly from a supermarket and grind it into small grains and apply it to the soil. And make sure you incorporate the charcoal into the soil by plowing. And typically speaking, we recommend that five percent of the charcoal to be mixed with the top 20 centimeters of soil. For example, if the soil density is 1.4 tons per cubic meter and according to that, probably you should calculate it according to the surface area. I mean, according to the size of your garden and calculate how much charcoal is needed. But generally speaking, five percent is good enough.

FLATOW: And also, you were talking about the fact that the charcoal will – is it absorb or adsorb the CO2?

Dr. GUO: I should say, it’s a mix of absorb and adsorb. It’s a mixture and we cannot distinguish the two terms. It is either physical adsorption or chemical absorption.

FLATOW: And the fact that it could absorb CO2 from the atmosphere…

Dr. GUO: Oh, yes. In that sense, it is not absorption. Actually, probably, you know that the original absorption of carbon dioxide from the atmosphere is carried out by plants, through photosynthesis.

FLATOW: Right.

Dr. GUO: But when plants die, the biomass will be decomposed quickly by microorganisms and release carbon dioxide to the atmosphere.

FLATOW: Right.

Dr. GUO: And once the biomass is converted into charcoal, and at least 50 percent of the carbon will be permanently fixed into that material, and it is resistant to microbial and chemical degradation. So that part of carbon will stay in the organic form and it won’t be released as carbon dioxide to the atmosphere.

FLATOW: So, you could take all the tree leaves and the corn stalks and the wood chips and turn them into charcoal and lock up a lot of that carbon in the charcoal, and create a great fertilizer at the same time.

Dr. GUO: Yes. Theoretically, all organic residues and wastes, including the grass leaves, crop residues, animal manure and yard trimmings, and even, you know, some leftover from the kitchen.

FLATOW: Wow. You know, people will say, but you have to burn this stuff to make charcoal. Does that not release CO2 back into the atmosphere?

Dr. GUO: The burning process, actually, it is not a real burning process because the materials are packed in a closed container and are heated at a relatively high temperature, say 750 degree F or 450 degree C.

FLATOW: Right. So there’s no oxygen in the reaction. You’re doing it without air.

Dr. GUO: Without oxygen.


Dr. GUO: Now, you know, only a tiny amount, a fraction, only about ten percent of the carbon will be converted to carbon dioxide. And 50 percent of the carbon will remain charcoal. And another 40 percent will be remaining as a byproduct called bio oil, which can be harvested and used as another renewable energy source.

FLATOW: And so, I know this is an ancient technique that was discovered in pre-Columbian tribes from the central Amazon. They were doing this 1,500 years ago.

Dr. GUO: Yes. We actually, we learned this lesson from the pre-Amazon people. An archeological event disclosed the fertile, charcoal carbon-rich and highly productive soil in the central Amazon basin. And later, scientific studies revealed that this fertile soil was fertilized by the Amazon people 1,500 years ago with char produced by smothering plant debris and annual bulbs(ph).

FLATOW: Ah. So the char, the fertilizer they made, the char they made 1,500 years ago, was still working?

Dr. GUO: Yes. The soil is still highly productive, even after 1,000 years of crop cultivation without any other fertilization.

FLATOW: Wow. Can farmers do this themselves? Can they make this charcoal themselves?

Dr. GUO: Yes. And on a farm scale, it is very simple. And the growth of the farmers, just have to pack the organic residues into a metal container and heat it at a like 300 or 400 degree C, until no visible smoke emitted. Then that charcoal is ready to apply.

FLATOW: Ah. So there must be a kit they can buy or some sort of – they must know how to do this, then. It’s not very hard to do.

Dr. GUO: It’s very easy. And actually, you know, 2,000 years ago, the Chinese people started to make charcoal by themselves by this kind of a process. We call it smothering or some, you know, paralysis.

FLATOW: Right. It almost sounds like the method to make coke, how people make coke.

Dr. GUO: Yes.

FLATOW: I don’t mean the drinking kind, either.

(Soundbite of laughter)

FLATOW: So where do you go from here in this research?

Dr. GUO: Currently, we are trying to extern this from the lab to the field scale. And we are going to do some demonstrations and to look at the long-term effect of charcoal fertilization, also quality improvement and the productivity enhancement. So when succeeded, we want to encourage all the farmers and growers around the world to practice the charcoal fertilization to improve soil quality.

FLATOW: Sounds like a simple thing to do.

Dr. GUO: Yes.

FLATOW: Thank you very much, Dr. Guo, for taking time to be with us.

Dr. GUO: Thank you. Bye-bye.

FLATOW: Bye-bye. Mingxin Guo, assistant professor in the Agriculture and Natural Resources Department at Delaware State University in Dover. We’re going to take a short break and come back.

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