What is Biochar? Should You Add it to Your Garden?

By Nicholas Clowers and Saffyre Falkenberg

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 ChelseaGreen.com.

“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.

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.