November 19, 2021

Learning How to Make Biochar

First, a bit of irony from something I wrote a year and a half ago.

"There are many good ideas for homesteaders out there, but they often require significant time and energy to maintain. Brewing compost tea or making biochar are two things I considered. They are excellent ideas, but would I be able to balance the time they required with everything else? Would I be able to provide all the components myself or must I continually buy something to maintain them? The answers to projects like this are subjective because there are many individualized factors to consider. We chose other soil building methods because they worked better for our homestead goals and routine."
"Re-evaluating Our Priorities," 5 Acres & A Dream The Sequel, pg 27.

The advice remains sound, but now I have to move biochar as an example into the never-say-never category! It was Dan, actually, who decided to undertake the project. We have a lot of waste wood, and the question is always what to do with it. How do we put it to good use?" The answer is to make biochar.

What is biochar and why would we want to learn to make it? Good questions!

What it is. Biochar (biocarbon) looks like natural charcoal (as opposed to commercially made briquettes), but it isn't. Charcoal contains wood resins, which make it combustible and give smoked food its flavor. Biochar is a step beyond charcoal. The resins have been baked out, leaving a stable, porous, carbon char. Its most common use is for soil building, where the pores become habitats for beneficial soil microorganisms and store water and nutrients.  

What it's used for. It has lots of uses.

  • In the garden (needs to be inoculated first - see below)
    • sequesters carbon
    • provides a habitat for beneficial soil microbes
    • retains soil moisture and nutrients (reducing runoff and erosion)
    • decreases soil acidity
    • removes soil contaminants such as hydrocarbons and heavy metals
    • increases microbial life
    • binds soil nutrients
    • improves physical structure of soil
    • provides long-term soil productivity
  • Water purification
    • rainwater tanks
    • greywater systems
    • aquaculture
  • In barns, kennels, cat litter, and composting toilets
    • odor control (absorbs ammonia)
    • absorbs moisture
    • reduces pH
  • Feed additive 
    • absorbs toxins in the digestive tract
    • improves digestion
    • improves feed efficiency 
    • reduces nutrient losses
    • reduces methane production
    • improves animals' overall health
  • Poultice additive to draw toxins out of a wound

How is it made? Biochar is made by heating biomass without oxygen. This is called pyrolysis and can be achieved in a number of ways. Some people make it by simply putting corncobs or woodchips in a lidded dutch oven on the stove and baking it. Others burn it in pits or in retort kilns. To make ours, Dan built a top-lit updraft kiln, also called a TLUD (tee-lud).

The TLUD is a type of gasifier and works just as the name says; it's lit at the top and draws air up from air holes in the bottom. It's not as complicated as it sounds! It's actually very simple. There are numerous variations on this, but this is how Dan made ours with two barrels with lids and some old ductwork.

Outer 55-gallon steel drum (burn barrel) with air holes
(primary air intake is at the bottom and secondary at the top.) 

Inner 30-gallon steel drum holds the biomass. Fire burns in the outer ring.  
(Note: This was our first try, and we've learned that smaller pieces work better.)

The wood inside the inner barrel will become our biochar. It is filled with "feedstock" (the biomass to be baked into biochar) and the lid put on the small barrel. Fuel wood is packed under and around the inner barrel, with kindling on top. The kindling is lit, and the chimney is placed on the top. 

A hole cut in the barrel lid accommodates the chimney.

The process goes through several stages.

Initially, smoke is emitted as the fire
burns out residual moisture in the wood.

The red glow indicates that the temp is
hot enough to begin burning wood gases.

Once the gases are burning well, there is no smoke.

The kiln is allowed to burn itself out, and once cool, the chimney is removed.

This is the biochar which is basically char with the wood resins burned away.

How do we know we've made biochar? 
  • Crushes easily
  • Has a fragile, almost tinkling sound
  • Has no smell or taste (it's sterile, so it's safe to eat)
  • When crushed with bare hands, the black residue washes off easily. With charcoal, residue is difficult to wash off because of the wood resins.

What other materials can be used to make biochar? 

  • corncobs
  • corn stalks
  • woodchips
  • twigs
  • bamboo
  • basically, any dried biomass; small pieces work best

How long does the process take? Once the TLUD is going, it needs no tending and will burn itself out in several hours. So the only time involved is in loading the barrels, starting the fire, and later unloading the biochar.

How do I inoculate it for the garden? Making biochar burns away all life and nutrients. So when first removed from the kiln, biochar is sterile and void. If added to garden soil at this stage, it will begin to absorb soil nutrients. Unfortunately, during this time it is competing with plants for those nutrients. Once charged with absorbed nutrients, it will begin feeding the soil, but the process takes at least 3 to 6 months. 

The best and quickest results are seen when biochar is inoculated (charged) first. There are a number of ways to do this:

  • Soak in liquid fertilizer. Fastest way, takes about a day.
    • compost tea
    • comfrey tea
    • nettle tea
    • manure tea
    • compost worm casting tea
  • Urine - place it in a bucket with drain holes and cover with pee. Takes 2-3 weeks
  • Mix 4 parts biochar, 1 part rock powder, 1 part worm castings, and ½ part flour or molasses. Cover. Takes at least 2 weeks.
  • Mix it into the compost pile (10-50%). Takes 2-3 weeks.
  • Deep litter. Mix it into the chicken litter in the coop, where it helps deodorize. It will be inoculated by the next time the coop is ready to be cleaned out.
  • Mix with equal parts fresh grass clippings. Cover and let sit until clippings are decomposed. Takes about 2 months.
  • Worm castings - equal parts with biochar. Sprinkle with flour, corn meal, or molasses. Cover. Takes about 2 weeks.

When I first looked at biochar years ago, I found only the complicated ways to inoculate it. As with all new endeavors on our homestead, it must be asked whether the benefit outweighs the time and expense. (See my post on "The Time to Benefit Ratio.") There are only so many hours in a day! Finding simpler ways to inoculate biochar changed that ratio. For us, simply adding it to the compost pile and deep litter significantly increased the benefit factor.

How do I apply it in the garden? Since ours is mixed in with the compost, I'll apply it as I do compost. I'll use it to cover seeds and top dressing. For new beds or transplants, I'll mix it into the soil. Some no-till people prefer to make slits in the soil with a shovel and sprinkle it in. It can also be tilled in or worked in by hand. Mixed with compost, it makes good potting soil.

Caveat. Various biochars are not equal, so results may vary. From what I've read, some benefit can be seen the first year of application, with continued improvement over the years.

Okay. That's all my notes about biochar! It isn't all there is to know, of course, and it's another fascinating subject to study. But it's a start and a good homestead solution for our woods and garden "waste." 


John said...

Hi Leigh,
An interesting post and something that I have not come across before. One question (the answer is probably in the post), the material used for the biochar is it green or seasoned? I am thinking particularly of hedge cuttings as this time of year I can collect large amounts due to my work.
kind regards,

Leigh said...

Hi John, welcome! That's a good question. The moisture in green cuttings will need to be dried out one way or another before they can burn. Putting green cuttings in the kiln will require more fuel wood, make more smoke, and take longer (for drying time) than by using seasoned cuttings. So if you have the time and room to let them dry naturally, that would probably be the better route to go.

Rajani Rehana said...

Super blog

Ed said...

There is an industrious fellow who lives not far away from the farm who started a number of years back collecting hedge tree fruit and extracting oil from the seeds to sell to cosmetic companies. Then last year, he dug a big trench in the ground, filled it with wood and then covered it over with soil again. The next time I drove by the place, the trench was open and on one end was probably a 20 feet tall pile of biochar. I have no idea what he plans to do with it. He seems to go into everything in a big way.

Rosalea said...

Very interesting and informative post, as always, Leigh. Dan is the Man, to give it a go!

Leigh said...

Rajani, thanks!

Ed, if it was me, I'd love to be able to add biochar to our pasture soil. It would take something like that to be able to make enough for that. More likely, your neighbor is going to sell it. A lot of gardeners are willing to buy it.

Thanks Rosalea! Now he wants to build a retort kiln to make biochar. That should be interesting too!

Rich said...

I started experimenting with biochar almost twenty years ago. Most of my biochar came from open burns, although I also used a simple TLUD for awhile.

I wrote a few blogposts about my TLUD and biochar on my long dormant blog at:

If you are starting out with biochar I'd suggest starting in a small area by applying a generous amount instead of just spreading a thin layer over the entire garden or mixing it into your compost pile. A good way to apply it would be to spread it in a strip about the width of your tiller, spread your fertility or mulch (compost, manure, fertilizer, etc.), then till it all together. Growing some sort of simple cover crop over the area before you plant your garden wouldn't hurt when you first start.

I usually put my biochar in something like a trashcan with drainage holes that I leave uncovered until it gets rained on for a while and "hydrates" everything and washes out some of the ash. In the past I've thrown a layer of manure or compost on top to let the rain wash it down through the biochar and innoculate everything (although I don;t think innoculate is the correct term).

I've seen some benefits from biochar and I encourage anyone interested in it do a little experimenting. I hope some of that helps.

Leigh said...

Rich, hello and welcome! Someone's experience is always helpful. So I very much appreciate your taking the time to share so many details with us. It's a great encouragement. Thank you!

John said...

Thank you for the reply Leigh, most helpful and also a thanks to Rich for his additional all helps. I shall be experimenting once my snapped collar bone has healed.

Cederq said...

Do you heat with wood Leigh? I have used the ashes from my wood stove and have mixed it into the compost pile and let it too age. Would that be the same as char? I don't burn trash wood or wood that has been processed and has glues, paints and resin in them.

Leigh said...

John, you're welcome! I love sharing and exchanging information with others. I hope you blog about your experiments. And I hope your collar bone heals quickly!

Kevin, yes, we heat with wood, and like you, we add the wood ash to the compost or sprinkle it onto a growing area. I think ash has benefit for the soil, but the biochar is really special. After the wood resins are burned away, the char structure is full of teeny tiny pores, kind of like honeycomb. It's those pores that absorb and store water and nutrients and become habitats for the soil microorganisms. So it offers a long-term benefit that ash doesn't. That being said, I'll continue to use both!

Toirdhealbheach Beucail said...

Very interesting Leigh, and something I had not really heard of or thought about at all (except by reading in your book, of course). It sounds in some respects like making charcoal.

Some years ago, I did some research for how traditional Japanese charcoal was made. Turns out a group in Canada restored an old 19th century charcoal pit built by Japanese immigrants:

Debby Riddle said...
This comment has been removed by the author.
Debby Riddle said...

The available options never cease to amaze me. I couldn't do anything large scale in this fire- prone climate, but a little batch in a dutch oven could be put to good use. Great information!.

Powell River Books said...

I've been away from blogging for a while. You are still doing amazing things. You make it sound easy, but biochar sounds a bit difficult to me. We are enjoying a month in Arizona, three weeks to go. The sun is a welcome change from our gray skies back home. - Margy

Chris said...

As always Leigh, I love the make-do with what you have inventions, you both seem to come up with. Just so practical and more importantly, does the job. It's a soil improver, you can control access too, in a world that seems to be running short on some things for soil building. Thankfully, nature has it covered.

Leigh said...

TB, that looks like one huge charcoal pit. I confess the pit method (for either charcoal or biochar) isn't all that appealing to me because of the added chore of digging it out. :)

Debby, I recently found a link to a video about making biochar in a woodstove - It looks pretty easy and very doable.

Margy, I confess we chose the easiest method we could find, lol. Glad you're having a good trip!

Chris, for us, it's becoming a great way to stack functions. We have so much scrap and deadfall wood here, that finding uses for it is definitely a good thing.

I've always believed in the natural cycles of creation, but even moreso as I watch the PDC lectures from Bill Mollison and Geoff Lawton's online course. Recovery truly is built into natural systems. If only we humans could get out of our own way long enough to observe and cooperate with these, we could do more to help and less to hinder with our good intentions.

Annie in Ocala said...

Excellent post! I have always heated with wood. Mostly in a wood stove but a few years in an open fireplace. And always spred the ash and charcoal bits on the pasture or garden, compost pile or chicken/pig pen. Long ago I noticed how some bits became nutrient accumulators and and others the critters would nibble on... What's not to love? Being in the vet medical field we've used activated charcoal to absorb toxins in suspect toxin cases forever (Literally I believe. And activated.... Hmmm. Might have to see what that's about!)
I have never intentionally made it but know that many bits left over from cleaning out the ash are perfect. Especially in my climate where the fire often gets choked down because it can be 42° in the mornings and 77° in the afternoons regularly.

Leigh said...

Annie, thank you! It's interesting that you've made your observations about char. I always start with research and experimentation, but it's those personal observations and experiences that really mean the most.

Anonymous said...

So I am from northeastern Oklahoma and have traveled to 27 different states in 2022 to various EPA,Brownsfeilds,and other conferences speaking on biochar and the benefits of carbon farming and remediation of soil and water and with the use of microbes how it works as a perfect hotel for the microbes as well so Ive been to several biochar plants and they run into the millions but this method will be very useful to me on my farm which year 2024 is going to be spent educating my community on the importance of carbon farming and natural health and wellness ...thank you for sharing it's very informative and if anyone needs a lead of microbes I got ya