Using Biochar to Increase your Garden's Yield

What is Biochar?

Biochar is essentially ordinary charcoal. It is made by heating wood in a low or zero oxygen environment. Charcoal has been made this way for thousands of years. There are more modern contraptions to make biochar, but it can be done with a simple bonfire, though that's not quite as efficient. On this page you find videos showing biochar making techniques as well as discussions and experiments that detail it's benefits. At Sylvan Gardens we are undertaking a small biochar experiment as well. I will describe our processes and results as we get them during the 2009 growing season. As I begin to craft this biochar page, it is near the end of the 2008 growing season.  Last night, September 18th, we had our first frost warning of the season.  Although we didn't get any frost last night (the outside temperature only dipped to 43 degrees fahrenheit during the overnight hours), every day from here on out is borrowed time for the less cold-hardy hardy plants in our vegetable gardens.

As we harvest and pull the summer's plants from the garden beds, we are preparing the soil for next year. That includes mixing in compost, manure, and this year, in some beds we'll add biochar. We'll compare the vigor of plants in the biochar beds against the ordinarily prepared soil trying to equalize all other treatments between the two areas. In previous years we have added fully burned wood ash as a source of potash for the soil, but biochar is different.  Instead of a powedery ash that is fully broken down by oxygenated burning, we are looking for chunks of biochar.  The highly porous structure of the biochar is wha tis believed to add the most benefit to the garden soil, but I'll get into more details later. Before we get too far ahead of ourselves, here's a video from YouTube that helped spark our interest in biochar as a soil additive. I'll talk about some of the information from the video so if you have a low bandwidth connection and don't want to try it, you won't miss too much.

The above video shows a dramatic increase in yield for garden plots with charcoal added to the soil. They compare against adding ordinary ash. In this particular experiment, mineral fertilizer was added to both plots as well. The results showed an incredible 880% increase in yield for the plots with bichar added as measured against those with just mineral fertilizer. Ordinary ash had a benefit for one harvest cycle only, and had no lasting benefit - unlike the biochar. The researcher in the video says that the biochar seems to hold the nutrients in the soil because of its open matrix-like structure. The minerals soak into the biochar and stay there instead of being leached out of the soil by rainwater. Others, like those researchers shown in the video below this paragraph, have suggested that the porous structure provides a huge amount of surface area upon which benficial soil microbes can grow.  Either way, dramatic increases in yield have been shown with the addition of biochar to the garden soil. It is also claimed that the structure of the biochar will absorb water and hold it in the soil, preventing the soil from drying out as quickly as it would without the biochar. That sounds plausible as well. I've always wondered how cities high in the Andes survived with the terraced gardens in what would certainly seem a difficult growing area. Since biochar, known in Central and South America as Terra Preta, has been found layered into the soil in ancient South American croplands, perhaps this technology was a major factor in the ability of these mountain farming cities to exist. Just speculation, but I'd love to pull some soil from the terraced Andean gardens and see if the Terra Preta technique was used there. Meanwhile, the video below also talks about the benefits of biochar both for the garden and for seqestering carbon and keeping it out of the atmosphere.  Although this group found a tripling of yield with the use of biochar, still a huge increase, they also focus on carbon neutral or even carbon negative practices to help reduce greenhouse gases in the atmosphere.

Biochar as Means of Reducing Greenhouse Gases

Once soil has been treated with biochar, it actually produced less carbon dioxide and nitrous oxide than untreated soil. I would guess that the biochar, which again, is just charcoal, in the soil acts just like a charcoal filter in an aquarium. It captures and locks the harmful gases or compounds within it's physical structure.  That's just my guess, but if correct then it would eventually reach a saturation point and new applications would be required to maintain the same level of ongoing carbon capture within the soil. This video doesn't get into the exact mecahnism by which biochar works to reduce greenhouse gas emissions from the soil, but they show very measurable and significant results.  They also show a biochar production factory on a pilot scale. Don't worry about the complexity of this for the time being. Further down the page, I'll provide much more information on how to more easily produce your own biochar.

While the scale on which you or I use biochar is not going to amount to much more than a hill of beans in terms of greenhouse gases, the use of biochar on large commercial farms could have a significant impact. I say this for several reasons. First it reduces the amount of chemical fertilizer that must be applied. Chemical fertilizer is made in a very energy intensive process that requires high heat and produces literally tons and tons of greenhouse gas pollution, so any reduction is beneficial. Second, it will increase the yield per acre of farmed land. This could help prevent forested land from being converted to farmland. Third, it helps soil produce year after year instead of just for season or two. In places like South America, this eliminates the need to move on to new farming plots which are carved from the rain forest with slash and burn techniques. Fourth, for home gardeners like you and me, we can grow more of our own produce locally, eliminating greenhouse gases that are produced as a result of transporting produce from distant places.

How to Make your own Biochar

So now we know why we should use biochar in our gardens: increased yield and it's good for the planet (and completely organic, by the way), so let's talk about how to make and use biochar in the garden. As we saw in the video above, biochar is created by heating wood in the absence of oxygen. You can do this in a fancy wood-gas fired furnace like the one in the video above. Of course, if you're like me, that's just too complicated and large-scale for you. I shudder to think about the permits required to build one of those in my town. So what can we do then. At Sylvan Gardens, it so happens that we have a relatively large area of forest on the property. That means a virtually unlimited supply of sticks and branches that either fall from trees or need to be disposed of when we cut down a tree for firewood to heat our heat. In years past, we've simply acquired a brush burning permit, piled up all the branches, and burned them in a big bonfire. As the fire starts to burn down, you are left with a big pile of glowing embers of various sizes that glow bright red as the flames die down. If we let these burn down to powder, we'll have ordinary ash. Of course we have some ash anyway, but we want to keep these burning embers intact, because they are biochar. As the fire burns down to embers, we spray it with water to put out the remaining flame, and stop the embers from reducing to ash. At this point they should be black and somewhat crumbly.  When cooled and dried, they'll look just like the biochar in the videos on this page. This method is not the most efficient way to convert wood to biochar- not by a longshot. Most of the wood will be reduced to ash, but epending upon the size of your fire, you'll end up with a good amount of biochar too. because it's not highly efficient, it also releases a high percentage of the carbon containe in the wood back into the atmosphere. However, the carbon that remains tied up as biochar will be locked into the soil for literally hundreds of years, so any biochar is better than letting the branches burn away into ash or even decomposing naturally. If you're more concerned with efficiency, or have a limited supply of wood to use for making biochar, here are two videos show alternate methods. The first still uses quite a lot of wood, the second is very efficient, but requires a little more construction and preparation.

Choose whatever method works best for you. You might also be able to salvage embers and biochar from a fireplace, however, a woodstove is designed to efficiently and thoroughly burn burn down to ash so you won't get nay biochar from a properly functioning woodstove.

The Biochar Experiment at Sylvan Gardens

At Sylvan gardens, as I have mentioned, we are trying biochar for the first time this year. In the fall of 2008, we'll add biochar to some of our raised bed or terraced gardens as we prepare the soil for next year. During the 2009 growing season, we'll post the results comparing the productivity of those plots with biochar added against those without biochar.  I'll also do the math conversions at some point since the two main videos above discuss adding biochar in terms of tons per hectare. I'll work that out to gallons per square foot so you can use an ordinary five gallon bucket to spread your biochar on your raised bed garden. Don't worry, if you're outside the US, I'll include a liters per square meter calculation as well. Come back here for the calculation later this fall, and for the results starting next summer. You already have Sylvan gardens bookmarked as one of yoru favorite sites, right?

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Unless otherwise indicated (such as the YouTube videos), the words and photos found on this website are copyrighted (Brad Sylvester,2008) with all rights reserved and may not be reproduced in any fashion without our express written permission. However, we will be liberal in granting that permission if you ask nicely, include acknowledgement of the source, and a link back to our website. The photos are our original property, if you’d like to use them for your own project, you must contact us for permission. They are also available in high resolution. brad@sylvangardens.com