Biochar: Adding Nutrients To Your Soil Naturally

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I’ve always been interested in historic methods used in farming, cooking, and healing. While I was reading through a few old magazines, I came across an article on biochar. Being interested in ancient methods, I did some more research and found that it was indeed something I wanted to try. So I continued my research and this is what I found…


What is biochar?

Biochar dates back thousands of years, perhaps even further. The earliest known reference to it comes from people who resided in the Amazon Rainforest from 500 BC up to the mid 1500’s when the European settlers arrived. It tells of pits dug into the earth, filled with wood, leaves, or anything that could be burned. After the fire began burning hot, a layer of soil was placed on top which smothered the flames. The wood continued to “cook,” charring it. When it was completely charred it would be doused with water to keep it from burning up completely. When cooled the charred wood was chipped up and plowed into the earth. The result was healthier, more productive plants such as cassava, maize and fruits.

Amazingly enough, these pits – or the results of them – can still be seen today. They are called “terra preta” or “Dark Earth.” The soils of the Amazon region are naturally rich in nutrients where the silt has been washed in from the annual flooding of the Amazon River. In other areas, this silt has been washed away, leaving less than desirable conditions. The people of the Amazon area in Brazil found a way to combat this. They made biochar from the dead wood and used it to revitalize the soil.

Benefits of biochar

Once added to the soil, by itself, biochar does nothing. However, when used along with organic fertilizers and compost, it has the ability to hold on to nutrients better than anything else. Charcoal has been used for hundreds of years as a filtering medium. This is due to the many holes or pores that the char has. Biochar -essentially the same as compost, but in a rough form – also has these pores. When wood ash breaks down, as smaller pieces of biochar and ash will do, it contains nitrogen, phosphorus, potassium, calcium and magnesium – all very essential to plant life.

Making your own biochar

So how do you make biochar? It’s very easy. Pick a spot in your garden away from anything that could burn. Be sure to choose a day that’s not windy or too low in humidity. Obtain a burning permit if necessary. Dig a trench large enough to accommodate the items you want to burn. Loosening the soil on the bottom of the pit will save time and effort later.

Don’t be too picky about the wood you choose, but remember green wood will take longer to char. Deposit the wood and scraps you want to burn into the pit. Start it on fire and keep a close eye on it.

At first the smoke will be white. This is the water vapor burning off. After a while, it will turn yellowish. The sugars in the wood are being burned off at this point. What you are watching for is when the smoke turns a bluish-gray. When you get to this stage, cover the wood with about an inch of soil. This will put out the flames while still allowing smoldering. Keep in mind wood needs an anaerobic (low oxygen) environment to char. Otherwise, it will just burn – and when burning is complete, char amounts lost are upwards of 80%. However, when making biochar, up to 50% of the char is retained.

(If you don’t want to dig a large pit burning can be done in a metal barrel. Just be sure there are no holes in it or oxygen will seep in and feed the fire. You can still throw soil over it if using a barrel. When it’s cool, simply tip it over and roll the char out.)

Once the biochar is done and the wood is all charred, douse it with water. This will stop the burning action. When it is cool, break it into pieces and turn it into the soil with some compost or organic fertilizer. How about some mushroom compost? Or beneficial bacteria? All of these can be contained by the biochar. Once you create your own biochar you’ll have:

  • more available nutrients for the plants,
  • reduced nutrient leaching into the soil,
  • reduced watering demands,
  • reduced soil acidity (but be careful, you may need to make your soil more acidic again for certain plants such as blueberries and rhododendrons),
  • reduced fertilizer requirements
  • and therefore, increased crop production.

And another bonus, when heavy metals are present in the soil, biochar, used at a 10% rate, has been shown to reduce heavy metals in the soil by up to 80%!

Consider this…

As another huge plus, CO2 gasses are retained when producing biochar so they don’t escape into the atmosphere and become part of the greenhouse effect. Imagine – if farmers across the globe were to start using biochar, a huge percentage of the carbon dioxide gas that escapes every day could be contained in the soil, where it would not harm the ozone layer and plants could make use of it as a nutrient. It’s hard to believe that such a simple thing could potentially mean so much.

I’m planning to burn a biochar pit this week. Now that I know all the benefits, with very little output, I’m going for it. After all, something that’s been around for over 3,000 years can’t be wrong!


Image source.

About Debra Maslowski

Debra is a master gardener, a certified herbalist, a natural living instructor, and more. She taught Matt and Betsy how to make soap so they decided to bring her on as a staff writer! Debra recently started an organic herb farm in the mountains of Western North Carolina. You can even purchase her handmade products on Amazon!

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  1. tad3c6b says

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  2. Sharon says

    We moved to a rural area about 5 years ago. We get a fair amount of friends staying for a weekend and we always have a fire as we all enjoy sitting out at night around it, how far away we sit depends on how hot or cool the weather is, lol. But, the fire always reaches a point where it’s more or less like charcoal pieces burning and we generally just let that burn all night and sometimes it’s still going 2 days later. Now I’m thinking we could just cover it with dirt at that point and put it out with water in the morning, then add it to our soil later. Do you need to mix it in right away? Or can we keep it till we’re ready for it?

  3. Debra Maslowski says

    I not sure if there’s a ational movement to provide people with biochar, but there sure should be! You could try finding someone locally who does it and maybe bartering. I’d trade milk or eggs for biochar any day! Another thought, I just bought a bag of compost that has biochar in it. It’s from a company called Harvest. Might be worth a shot.

  4. Kendahl @ Our Nourishing Roots says

    I didn’t know this about biochar until reading your post, so thank you! We are starting to plant a lot of things around here lately before it gets too hot. We’re going to be looking for some biochar to help out the soil in our backyard now.

  5. Jim says

    This sounds like an interesting idea that I could incorporate into my developments. I live on a river bank and there is some great soil in between the very abundant rocks.

    It takes me a year of composting to make sufficient to replace the rock volume dug out of a couple of 4×8 raised beds! I have a question though.

    Are we talking burning logs here or can I do this with all the small stuff from trimming trees that I have felled?

    • Debra Maslowski says

      You can use whatever you want. Smaller twigs will burn faster if you mix them with larger pieces, so I’d suggest keeping all of what you do at one time around the same size. I don’t have a solution for the rocks, though. Wish I did. Some of us have that problem here!

  6. Cooper Boone says

    When is the biochar considered “done”? On average, how do you know when the wood is charred or on average how long do you let it smolder?

    Thanks – Cooper

    • Debra Maslowski says

      You should burn the wood until the flames turn blueish-gray. This is when the sugars have been burned and the water vapor is gone. Then cover it with about an inch of soil. Leave it until all the wood is charred, but not burnt up. You’re looking for something that looks like charcoal (because it is!) or charred wood. The amount of time depends on the wood used and the age of the wood. Green wood takes longer than dry wood. And hardwoods take longer that softer woods. The type doesn’t really matter. When you get to that point, pour water over it to stop the process. When it’s cool, allow it to dry out and store it in a dry place. Or add it to the soil right away.

  7. sylvia waters says

    What a great idea for all the twigs and tree trimmings that were being tossed into the garbage. My soil could definitly use some natural nutrients.

    • Debra Maslowski says

      I think the newest Organic Gardening issue has an article on biochar. Geat reinforcement! and I was at Lowe’s in Marion, North Carolina a few days ago and saw a bag of compost that contained biochar. Certainly not a new idea!

  8. Charles says

    The use of a simple home made biochar reactor will greatly increase the production of biochar (up to 80% biochar vs 50% for pit burn) and reduce the production of co2 and other greenhouse gasses during the burning cycle. Youtube has several good instructional videos for simple to build biochar reactors made from scrap materials available for free or cheap. I made mine from a 55 gallon barrel, an old water heater core and some spare chimney pipe I had laying around and an afternoon of cutting and drilling. Biochar is THE ONLY proven method of carbon sequestration and can be adapted for both home and commercial electricity production as well as over the road transportation that is CARBON NEGATIVE!

    • Debra Maslowski says

      Thanks Charles! I love the idea of making a reactor. And you’ve gotta love Youtube! There is so much information out there. Great information!

  9. Anne says

    Is there any benefit to adding ashes from the fireplace to the garden soil?

    • Debra Maslowski says

      You can add ashes, but you won’t get the same effect. Ashes are wood that’s completely burned, not leaving any of the pores for the bacteria and nutrients to hang out in. And too much ash can raise the ph of your soil. Small amounts are fine though. In a 5×5 raised bed, a few cups worked in are just fine.