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What Is Biochar and How Can It Improve Your Cannabis Garden?

December 18, 2017
(Oregon Department of Forestry/Flickr Creative Commons)
Biochar has been used for centuries, and it’s making a comeback in the past few decades among farmers. Created in a process known as pyrolysis, biochar is a carbon-rich charcoal soil amendment that may help to address some modern environmental challenges.

To learn more about biochar and its impact on sustainable growing practices, we spoke with Miller Soils, who produces biochar-based blends out of Colorado. 

What Are Biochar’s Benefits in the Garden?

Sunny Kaercher of Miller Soils describes biochar as “giving your soil food web a habitat.” In other words, the large surface area of biochar offers endless nooks and crannies for bacteria and fungi to live and develop, thus protecting and promoting growth of small organisms in your soil’s food web. These organisms are vital to a healthy soil by making nutrients available to your roots while also helping to boost the immune system of your plants.


What is super soil and how do you make it?

Microorganisms are not the only things that occupy the surface area of biochar. Through a process known as CEC (cation exchange capacity), water and nutrients are both drawn to biochar. “Most of your major nutrients have a positive charge and water has a bipolar charge, while biochar offers a negative charge,” Kaercher told Leafly. “Because of this, the biochar attracts the nutrients and water. They want to link up.” This linkup ensures your soil holds onto the water and nutrients, keeping them available for your roots to intake as needed.

What’s the Difference Between Biochar, Charcoal, and Activated Charcoal?

Biochar shares similar properties with both charcoal and activated charcoal, but its unique properties better serve as a soil amendment. Charcoal is produced to be used as a carbon-rich fuel, while biochar harnesses carbon’s ability to provide large amounts of surface area. Biochar does not share the same bulk density or hardness as activated charcoal. In this way, it has less of a surface area than activated charcoal, but is easy to produce and work into your soil. 


A Simple Super Soil Recipe for Your Cannabis

How Is Biochar Produced?

Biochar is produced in a kiln. This process can take place on a range of scales from DIY to an industrial plant. Regardless of the scale, biochar requires biomass (organic material) to be produced. This biomass can be sourced sustainably through forest fire fuel management work or from your own yard waste.

On a large scale, you can see the full benefits of biochar. Miller Soils generally uses large dead pine snags that were destroyed by the mountain pine beetle in Colorado. Once harvested, the snags are processed into chips that will be moved through the kiln where the biomass is baked. As the biomass bakes, it releases syngas (synthetic gas) that is captured and cleaned to fuel the kiln, or it can be used as a natural gas.


How to Maintain/Amend Your Super Soil Mix

Small-scale farmers can build kilns that catch the gas being released from the biomass. These systems generally involve creating a fire around a metal container that will hold the biomass. Gas from the biomass is released and then caught to help fuel the fire, reducing the necessary input of heat. 

What Are Biochar’s Environmental Benefits?

Forest Management

Biochar helps remove dead snags and biomass debris from forests. This plays a large role in forest fire management by removing fuel that is responsible for dangerous and devastating wildfires, especially in states like Colorado where debris is so abundant.

Sequestering Carbon

Snags that are left in the forest not only provide fuel to wildfires, they also release high levels of CO2 gas into the atmosphere when they burn. By producing biochar, you’re putting carbon back into the earth in a stable form that will not release into the atmosphere while also providing a home for microorganisms to develop complex soils that further sequester carbon as the organisms live and die.


Sustainable Gardening Practices for Growing Cannabis

Soil Fertility

Biochar as an amendment helps to rebuild soil that has been eroded through industrial agriculture. Its presence aids in sequestering the organisms, nutrients, and water that help prevent the runoff responsible for nutrient blooms in our rivers, lakes, and oceans. Preventing runoff means fewer inputs, which helps save water, nutrients, and soil by ensuring what you put in is being preserved. Additionally, a healthy soil is a carbon sink; the plants pull CO2 from the atmosphere and sequester it in the soil, helping to lower the levels of CO2 in our atmosphere.

As an amendment that is easy and cost-effective to produce, biochar’s reach is endless. In regions of Africa, for instance, where soil fertility has been destroyed over the past century, biochar can help to start rebuilding these damaged soils while keeping the water and nutrients in the ground.

Do you have any experience working with biochar in your cannabis garden? Share your experience or questions in the comments section below.

Trevor Hennings's Bio Image

Trevor Hennings

Trevor is a freelance writer and photographer. He has spent years in California working in the cannabis industry.

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  • les

    I love it when people recommend something that”may” work….. you need to do more homework on this controversial subject. And snags in forest decompose to feed the life of the local environment. The CO2 is fuel for the trees and plants as it is mostly trapped under the canopy. Removing/burning snags is more harmful to the environment than this so called biochar is helpful to your canna soil! Hey! Why don’t we burn or compost those soybeans that are destroying the Amazonian Rain Forrest, you know, they ones all the health nuts and vegan think are so great. Did you know, 1,000,000 acres a day of rain forest are destroyed to grow soybeans………. as stupid as this boichar craze!

    • bonbonfire

      Thanks to Les for the comment. I was trying to keep an open mind about it as I read the article, but had the same thoughts. I live in a rural area with 80 acres of forest and have observed for decades how these snags and forest “debris “act as habitat for animals as well as soil build up in a healthy forest. On the other hand we now have Sudden Oak Death (SOD) that has caused many Tan Oaks to die and actually are creating a fire concern. All depends on the forest’s health AND the understanding of the forest manager. (And yeah…what about millions of acres of primate habitat cleared for palm oil. Check labels and don’t buy it.)

    • Mike Morrison

      Well said Les, my thoughts exactly!

    • E.L. Bl/Du

      HI Les, I was wondering about this too, as Im continually surprised at all the crazy stuff some of these new growers are coming up with. I also think that ppl who use bat guano are adding to the introduction of disease to the bats in America when they harvest it without being careful not to contaminate the habitat. They are dying in large numbers from a fungus they contracted in the past 5-10 yrs, Hmm, think there is a connection? They eat 100 mosquitos/minute if they had them available. Now with the intro of Ebola and Zika we need them more than ever. But not if some dumb ass trying to “get in” on the “new” fad or the gold rush think they HAVE to have bat guano instead of getting smart about how to garden organicly, sustainablely and not do something that has a consequence down the line. (like chemical fertilizers) ITs ALL about COMMON SENSE! BTW, allot of those soy beans are owned by MONSANTO! did you know that? (sorry) I just wish more ppl would use comon sense when they read allot of these articles, not all of it is true. Its ONE GUYS OPINION. Lets see some statistics….right?

  • Kelpie Wilson

    I got involved with biochar here in Oregon years ago when I saw how much smoke was produced by burn piles every year. I wondered if there was a way to avoid the smoke and make biochar. I developed a kiln to do that, and you can see it at This stuff is being burned anyway, so the net result is that we keep carbon out of the atmosphere and put it in the soil where it can do a lot of good. I get great results using biochar in my garden, especially when I compost it with high N organics. Biochar helps hold nutrients in the root zone of plants and provides soil structure and waterholding capacity so you can skip the perlite.

  • Some uneducated individuals below are trying to claim that biochar is bad.

    The Amazonian indians have been doing it for thousands of years.

    I think we can trust them over some internet know-it-all.

  • Urban

    I use biochar as part of my supersoil formula in air pots to help hold the water since air pots tend to dry out quickly. With about 15% biochar the soil can hold enormous amounts of water without compromising air spaces or drainage–along with all the other advantages such a increasing cation exchange rate and conserving fertilizer. I cook the biochar for a month or so with worm castings, compost, high phosphorus seabird guano. langeneite, azomite, ruby mountain rock dust, kelp, and filtered water. This gets mixed with the rest of my soil before potting. I water with humic acids, kelp, and yucca as a spreader sticker to help absorption, and very small amounts of fish hydrosylate and molasses to feed the soil life but use no fertilizer until after early flowering when I add mononotasium phosphate as a bloom booster with plants that are heavy PK feeders. Air pots are tricky but once mastered produce a root ball far denser than smart pots which I had used for the previous five years. A large and dense root system is hey to large yield. Biochar and watering slowly with a spreader sticker make an enormous difference and when used with air pots can go a long way towards getting hydo yields with the higher quality I and others associate with a sophistcated organic soil grow.

    • Congo

      I am interested in rates, and how much to use in a soil mix that has been used and fairly depleted of nutrients from several years of use. When you say “with %15 bio char”, is this the total percentage of your soil mix? i.e. if you have 10 gallon pot you would use 1.5 gallons of Bio Char?

      • Urban

        Yes. I no longer re-use soil as I found that no matter what I did to renew it the soil didn’t produce like it had the first time. I now add the used soil to my outdoor garden where it continues to contribute.

  • Congo

    I am interested in min and max rates for Bio Char for depleted soil, and to avoid high pH rise.