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FAQ for biochar

You sometimes use biochar and charcoal interchangeably- is there a difference? Biochar is a fairly new term coined by scientists in order to make a distinction: Charcoal is a cooking and industrial fuel and filtration product and biochar is intended for use in the soil. is working on a definition for biochar.

Making charcoal is smoky and polluting, isn’t it??? Like so many things there are many ways to make biochar or charcoal. In the past much charcoal was made by smoldering- a slow and very smoky process. I do not recommend this. Smoke is wasted energy and often makes the neighbors unhappy. One can make in a retort, a TLUD (top lit updraft) gasifier on a small or larger scale. Look for these and many options on YouTube. This is a way that works for us:

How can burning something be good for the atmosphere??? Tough one. When one makes biochar you’re basically only burning the feedstock material about halfway. In the pyrolysis process the volatiles- water, sugar, starches, tars+++ are gasified- smoked off as it were. About 50% of the original carbon then remains as biochar- and this 50% will be long term recalcitrant in the soil. Compare this to, say a pile of wood chips or yard waste decaying. 100% of that carbon will usually return to the atmosphere via microbial and fungal decomposition as CO2 in 5 years or so. In our biochar case, if added to soil 50% of this carbon is “fixed” and will not return to the atmosphere for a good long time. Of course every batch of biochar will have different characteristics and some will last longer than others.

Didn’t I read somewhere that claims for biochar as a “miracle cure” or “magic bullet” are overblown?? Yes surely there are folks out there who are so excited by the potential of biochar that some wild claims have been floated- and this is unfortunate. We’re not making such claims. It is important to note that any good thing can be done poorly or stupidly. The way that Ethanol was promoted and subsidized and the effects this has had on food prices, farmlands, farm soils, biodiversity, water quality, etc serves as a cautionary tale. Some have claimed that “Biochar lasts thousands of years in the soil” It’s true it can, and has, in many of the terra preta and other ancient soils studied. That much is settled science. Does that mean that every batch will last many thousands of years? Not always, and not necessarily every time, we’re still learning. A LOT depends on how it’s made, how hot, how fast, what type of device employed, choice of feedstock, etc.

New ideas that scale up rapidly to industrial size often bring with them new unforeseen problems. Our friends at Biochar International also have an excellent discussion on these and other claims at:

Is biochar the only way to store carbon in soils??Certainly not. Intensive Management- Holistic Management or “mob grazing”, Keyline Farming, Perennial Agriculture, building of the Soil Foodweb and Agroforestry are all excellent strategies that help build carbon rich and naturally productive soils. For more info visit: Reforestation is also most helpful and critically needed- plant your lawn!

So what??? Just keeping a bit of carbon out of the atmosphere for a good long while doesn’t sound like much. Well point taken. We’re looking to propagate the idea that the soil is the most productive possible place to put extra carbon. Biochar as a recalcitrant (resistant to microbial decay) form of carbon can help one use fertility more efficiently- adding its sponge capacity to soil and holding nutrients in plant available form. So we can garden, farm and have nursery production with less fertility, higher water quality outcomes and build soil carbon. Not so small when you think about it.

Can I add too much? I’d say that 5% by volume seems like a good beginning threshold. Up to a total of 15% often seems to be the point where one gets diminishing returns if one continues to add more. In the garden I add biochar that’s been inoculated by being mixed for 2-3 months with an active compost to the soil. I add 1”-2” to top off raised beds and basically pretend its compost- but the biochar stays and gets to be a more integral part of the living soil as time goes by.

Is it a fertilizer?? No. Look at it as a soil catalyst, something that augments the effectiveness of and works well with many other forms of nutrients and minerals, helping to keep them plant available. With its extremely high surface area and both cation and anion exchange sites it can act as an enhancer- helping to build long term biologically based living productive soils.

Can I make some charcoal and add it right to potting soil or a garden bed? Not recommended. You often can get away with adding and tilling in fresh biochar to gardens in the fall. By spring the biochar is “filled up” with nutrients and friendly soil micro critters and it likely will go fine. If you were to create fresh biochar and add it right to soils- potted plants or to an actively growing garden- it likely would not be helpful at first. It turns out that charcoal or biochar is a very adsorbent material. It would likely out-compete the roots for available nutrients. That’s why we prefer to inoculate the biochar- with an active compost- compost tea or other biologically active materials and then let it sit for 2-3 months and work its way into the biochar. Then it will “play nice” with your crops.

Isn’t it better to just make compost out of a given amount of biomass? The world surely needs more compost and composting! And certainly millions and millions more trees! There’s a time and a place for everything and I suppose a highest and best use of a given bit of biomass. It turns out that the best answer isn’t either or but both. They work together like a hand and a glove. A lot of biomass can and should be composted. Some fraction of waste biomass like tree and orchard trimmings, forestry slash, municipal wood chips, etc could also be used for cooking, creating carbon negative energy and making biochar at the same time.

Are there other environmental advantages of adding biochar to garden or potting soils??? Yes, research has shown that it can help provide habitat for and increase populations of the symbiotic bacteria that legumes use to fix nitrogen in the soil. Other research has shown that it can significantly lower farm soil emissions of nitrous oxide and ammonia. The added “sponge capacity” that biochar brings to soils can keep plant nutrients where we want them- in the soil- rather than having them run off as pollutants. If more gardeners and farmers added it to their soils the water would be cleaner. For more info see:

Why haven’t I heard of this before??? Believe it or not- the science of this is quite a new subject.  In the early 90’s scientists working in the Amazon basin found many old village sites with lovely black soil- terra preta. These soils were rich in carbon and brown to black- still fertile after 500 or more years of neglect. They were determined to be anthropogenic- or man made soils. They often had a major component of biochar in them.