Iron Chef Biochar edition? Thought Experiment

First of all Hi! I'm new here (i think this is only my 3 post) and i'm like Alice following the rabbit. I have a thought experiment that i want to try out in real life but wanted your input first, oh sage ones!

I live in Fl and am in the process of building 3 raised hugelkulture beds. I now (finally!) understand of having good soil (with micro organisms, nutrients and good water holding characteristics) to successfully garden.
To that end, I want bio-char. enough for the 3 beds and an easyish way to get it in the future for all my other gardening needs. I live in an urban setting so 55 gal retort is not an option and tlud making is out of my comfort zone at the moment.

So, it's 3:40 am and after reading every post and reply on bio-char that  i could get my hands on and watching too many YouTube videos, here's what i have in mind:

Get a bag of B&B 100% natural charcoal briquettes from ACE hardware (i'm not trying to advertise, that's where you find it. if this is not allowed, i'm sorry. please don't hurt me) PROS- no additives only charcoal dust and cornstarch binder. when soaked it will break down into a sludge which means i won't have to smash it. also it already has been captured as a byproduct of coal making so i don't have to put more CO2 into air by making my own?)

Alternative option would be to use rice coal (Anthracite) but it's mined, so i'm unsure as to how it compares to the briquettes.

Put coal in 5 gal bucket and cover (soak) in urine for as long as it takes to start smelling a little (2 weeks?)

combine with a slurry of kitty litter and either sea water or rain water. from what I've read Purina's Tidy Cat's free and clear has (a percentage, how much unknown) of Sodium Bentonite clay, plus charcoal, and baking soda. No other chemicals. But there's also Cat's Pride Fresh and light and Catit multi cat (which has scent crystals? but its also 100% Sodium Bentonite)

At this point I want to be able to use the bio-char in to the beds as soon as possible so either a) I mix it 50-50 with Compost/manure (I couldn't find a pic. i got it at Home Depot. It's not KOW. it was approx $2.50/bag? I don't think the cow manure in it is 100% composted (so it's still hot) or make Compost Tea and soak the charcoal + Sodium Bentonite mix in it?

Also would like to add some Epsom Salts? and blood meal? also Sea water?

Finally I want to add worm castings but I've not gone through my bins yet and in any case i gotta dry it out a bit in cardboard boxes before i sift it. then add with some flour and molasses

So what do you all think? crazy?

Coal is not charcoal, is not biochar.

Biochar's benefits come largely from the porous microstructure, which adsorbs and releases nutrients and acts as a home for soil bacteria and fungi. This porous structure comes about because of the very nature of the charring process.

What differentiates charcoal from biochar is the presence of the active soil bacteria, nutrients and other biological goodies. For maximum benefit charcoal should be "charged" with nutrients - for example by mixing it with an active compost heap, adding manure or similar.

Most people who use biochar make their own, usually from some kind of waste material that they have to hand - in my case woody brash from pruning trees and hedges, that is not suitable for composting. It combines waste disposal with making a useful material. But I wouldn't personally buy in any form of manufactured charcoal/biochar from off-site; there are other materials I would be more interested in first like manure, spoiled hay and straw, wood chips etc... that build soil life and carbon rapidly.

Very quick reply, the "rice coal" you mention there is not charcoal, it will not do the same thing and is not something you want to add to your soil. If you want to buy a charcoal to make biochar you should probably buy a lump charcoal as it is the structure you need to house the bacteria/fungi and I doubt that the finely milled charcoal in the briquettes will have the same effect.

yes i understand that coal is not biochar and that lump is best, but in this particular case, the briquettes don't have any additives other than being bound by cornstarch so why wouldn't it work (once inoculated/activated, ofcourse) and thanks for the info on rice coal; so that's off the menu.

Would charcoal briquettes work? Maybe, but it would help to clarify what you mean by "work" in this context. Do you mean "add a healthy substrate that will help soil bacterial thrive" or do you mean "not be actively harmful to my growing plants".

I think it would be safe, with regards the latter, but I'm not convinced it would be worth the expense for the former. You say it has no additives, but the very conditions of charcoal making are such that it may not be desirable as a soil amendment. I have personally made charcoal to use as biochar, to use as fuel for melting aluminium, and for use on a BBQ. The qualities of these products are very different.

When making charcoal to use as a fuel you want to heat it just enough to pyrolyse the wood, but without burning away too much of the mass. This is a fine balancing act - someone selling briquettes by mass wants a product that is just pyrolysed enough to be usable, but no more than that - going beyond that point burns more of the woody material away directly impacting profits. Secondly, the materials they use for a briquette may not be ideal - do they use pristene timber products, or is their fuel a mixed source including potentially treated/painted lumber? At least with lumpwood charcoal you know it has come from actual trees.

By contrast, when making biochar you want to pyrolyse it substantially beyond the minimum level described above. You are aiming to burn away most of the volatile material, leaving the porous char behind. The end result is lightweight, leaves your hands clean when you handle it and feels almost "glassy". It is brittle to the touch and makes a tinkling sound when you knock chunks together. It is chemically quite different as well - burning off those volatile compounds makes the remaining char very unreactive and stable. The volatile can be biologically active and contain many compounds that may impact living organisms (compounds that are commonly found in fossil fuels like benzene etc...).

OK! 😊 thank you! Now I understand that the cooking method of making the coal matters. Thanks, Mike, for taking the time to explain it to me. So now I want to continue with this thought experiment but using 100% natural lump coal. I know that it doesn’t account for the quality of the wood but at least I’ll be able to see if the lump clinks like glass and doesn’t have an oily residue. I’ll have to break it up before using it and that means a mask or driving over it, or both. What about the rest of the steps? What would you change or is it ok as is?

I'm, not sure why you want to use cat litter?  If you mix cat litter with water and anything, you are going to have a brick.  If you aren't comfortable making charcoal, I would buy the natural charcoal you were talking about, mix it with urine, compost, manure, or worm castings (or all) and use it like that.  I wouldn't use cat litter.  

Hi Trace, there was a post regarding the use
of sodium benonite clay in addition to bio char to add to the water retention capabilities. http://www.plantsman.com.au/page2/files/Plantsman%20Adding%20clay.pdf
(Thanks, Nancy Sutton) You mix 2 lb (1kg) in a bucket and you fill it 3/4 w/ water and you then spread it over 3 sqft (1 meter).  

Vanessa Alarcon wrote:Hi Trace, there was a post regarding the use
of sodium benonite clay in addition to bio char to add to the water retention capabilities. http://www.plantsman.com.au/page2/files/Plantsman%20Adding%20clay.pdf
(Thanks, Nancy Sutton) You mix 2 lb (1kg) in a bucket and you fill it 3/4 w/ water and you then spread it over 3 sqft (1 meter).  

Gotcha.  Again, things are so site-specific.  I can see it if you have very sandy soil, which seems to be your situation.  In my soil, I would be making little ponds

Exactly, Trace.  My soil is also very sandy, and my drainage is too fast!   So I'm always looking for a way to hold water. * Organic material (compost) works, but must be constantly replaced (& I'm old : ); adding clay, i.e., bentonite cheap kitty litter (but minus bicarb soda as it is very alkaline... would have to check pH, I think)..plus Eliot Coleman advised adding bentonite, citing some German soil studies (will find and post, if desired); and then biochar.  There's also the benefit of holding 'soil nutrients' ... for centuries!    (*hugel, I know, but I need hugel 'holes', not raised beds... which I do make, burying wood, along with the biochar, clay etc)

Also, IIRC, the Latin American terra preta contained clay pottery pieces (these were in midden sites), so I figured maybe that was part of the benefit, and adding clay might have 2 benefits - holding water and soil 'enrichment'.  All depends on your original soil, I think.... it would take a LOT of clay to make my sandy soil 'brick-like' : )

I'm not looking for perfection, so I like the convenience and economy of using 'natural' briquettes (see my old post re: the coppiced (renewed) tropical hardwoods source) and cheap, un-amended bentonite clay cat litter.  Of course... even cheaper, is burning one's prunings in a TLUD or even the open trench method shown on Mother Earth site... or the cone designs, etc.  (Hoping to try this this winter.... Edible Acres YT shows one experiment)  All this being useful for the urban, suburban, small lot gardener et al.

(PS - thanks for another source for 'natural' briq's - as Trader Joe's have gone up in price!, and the link.  I think a 'wetting agent' mentioned might just be very dilute pure soap solution,  and sodium bentonite  - clumping litter - might have more holding capacity than calcium per Erica Strauss' research.  I'm motivated by the possibility that easy and cheap irrigation might not be the case anymore at some point in the future.

BTW, I found cheapest clumping clay-only litter at a Tractor Supply store... caters to 'hobby' farm types with livestock and also pet businesses.. i.e., lots of cats : )  I'm in the Seattle-Tacoma area of Washington State, and bought the Paws & Claws brand, 40 lb box.. on sale for $10, 2 yrs ago.  It is also carried by 'drilling supply' stores, sold in big bags...to line bore holes, as it is very impervious when wet (many years ago I got some 'broken bags' for pennies.. but business moved).

Yay! 🤩 Thanks Ms. Sutton! I really like your ideas! And thanks for the alternate source of clay. I just could not find anything w/o baking soda!  As far as making this biochar for a small scale urban gardener, I know it’s more expensive than burning your own wood but at least it’s not as expensive as buying Biochar online. And it’s so nice to be able to make a small batch when you need it instead of having to deal with storing un-activated (not inoculated) biochar, which can be a fire hazard.

Just a thought re "buying biochar when you need it"

From your comments I believe that you are thinking of biochar as rather like a fertiliser - you add it to the soil when setting up a new bed, or at certain times of year or under certain conditions. It doesn't really act like any other fertiliser, or soil additive. Instead of being something that is used up it permanently changes the soil structure, making it biologically more active and allowing the soil to store and release more nutrients (as opposed to leaching away).

I take the view that adding biochar to my soil is like a 10 to 20 year investment. I'm not counting on any particular benefits in a particular growing season, and I see no reason to add it at a certain time, or under certain conditions - or even applying it with any consistent method. In practice I make char when I have woody material I need to dispose of, and topdress it thinly in my planting areas at any time. The natural cycle of soil disturbance - planting, harvesting, worms, moles, birds scratching etc... - cycle that char material down into the soil where it becomes integrated into the root zone over a few seasons.  Plus I top dress regularly with compost, spoiled hay or other mulch burying it directly. These days I don't intentionally dig it in; although I might take the time to add some if I am digging soil for other reasons.  I also don't take special efforts to charge my biochar; I know that my soil is full of active bacteria and fungi that will quickly colonise it, and I add nutrients through other means (compost).

This approach means that I never "need" biochar; it is a fortuitous event when I can make some, and I take advantage of it, but I don't go out of my way to spend money or effort on the process.


This thread has my experience making biochar at home using a simple low cost trench method.


Making char


The resulting pile - quenched with water, allowed to sit for a few days, then top dressed 1/4" thick over the growing beds.

Michael Cox wrote:Just a thought re "buying biochar when you need it"

From your comments I believe that you are thinking of biochar as rather like a fertiliser - you add it to the soil when setting up a new bed, or at certain times of year or under certain conditions. It doesn't really act like any other fertiliser, or soil additive. Instead of being something that is used up it permanently changes the soil structure, making it biologically more active and allowing the soil to store and release more nutrients (as opposed to leaching away).

I take the view that adding biochar to my soil is like a 10 to 20 year investment. I'm not counting on any particular benefits in a particular growing season, and I see no reason to add it at a certain time, or under certain conditions - or even applying it with any consistent method. In practice I make char when I have woody material I need to dispose of, and topdress it thinly in my planting areas at any time. The natural cycle of soil disturbance - planting, harvesting, worms, moles, birds scratching etc... - cycle that char material down into the soil where it becomes integrated into the root zone over a few seasons.  Plus I top dress regularly with compost, spoiled hay or other mulch burying it directly. These days I don't intentionally dig it in; although I might take the time to add some if I am digging soil for other reasons.  I also don't take special efforts to charge my biochar; I know that my soil is full of active bacteria and fungi that will quickly colonise it, and I add nutrients through other means (compost).

This approach means that I never "need" biochar; it is a fortuitous event when I can make some, and I take advantage of it, but I don't go out of my way to spend money or effort on the process.


This thread has my experience making biochar at home using a simple low cost trench method.


Making char


The resulting pile - quenched with water, allowed to sit for a few days, then top dressed 1/4" thick over the growing beds.

I feel the way you do about this.  That's part of the reason I don't concern myself overly much with crushing it.  I run over mine with a truck a few times and mix it in with my compost or chicken bedding.  My thought process is that the freeze/thaw cycles of my winters will do the rest of the crushing for me.  Biochar for me is a long term plan, as you said.  I make it, mix it in with whatever organics I have, and trust in Mother Nature to take care of the rest.

Michael Cox wrote:Just a thought re "buying biochar when you need it"

From your comments I believe that you are thinking of biochar as rather like a fertiliser - you add it to the soil when setting up a new bed, or at certain times of year or under certain conditions. It doesn't really act like any other fertiliser, or soil additive. Instead of being something that is used up it permanently changes the soil structure, making it biologically more active and allowing the soil to store and release more nutrients (as opposed to leaching away).

Hi, Michael, let me explain myself. I live in an urban setting (city), so when I say "biochar when you need it" I mean "The ability to have biochar available to amend a newly formed bed for long term biodiversity". For example, this year i'm building 3 raised beds filled in a hugelkultur way with old and new wood. I feel that this is the right time to add biochar, along with other nutrients, compost etc, so that each bed will have the best possible start. Also, I don't expect a new bed to produce gangbusters in the first few years. This is a long time investment for good, healthy soil. Currently all i have is sand, seriously!. and although by some miracle we do have plants in our landscape that somehow have managed to hang on (feeding off of what? wHO KNOWS!) I know that every grain of soil around my house needs to be helped and cared for. and if i can combine some ingredients for a reasonable price, why not?  About the only good thing i've got going for me is that our house sat abandoned for a long time before we bought it, so no pesticides or chemicals were used to take care of the yard then, and i've always been too cheap to buy any of those chemicals now. so i guess that worked in my favor (lol!)

But to go back, if at the end of my life, i leave this soil holding on to nutrients, rather than them running through it like a sieve, i'll feel i have done my job.

Great pics, btw!

Vanessa Alarcon wrote:
"The ability to have biochar available to amend a newly formed bed for long term biodiversity". For example, this year i'm building 3 raised beds filled in a hugelkultur way with old and new wood. I feel that this is the right time to add biochar, along with other nutrients, compost etc, so that each bed will have the best possible start. Also, I don't expect a new bed to produce gangbusters in the first few years. This is a long time investment for good, healthy soil. Currently all i have is sand, seriously!.....

But to go back, if at the end of my life, i leave this soil holding on to nutrients, rather than them running through it like a sieve, i'll feel i have done my job.

Great pics, btw!

All I'm getting at is that the availability of biochar need not be a barrier to getting everything going. Make your new bed. If you have some available add it there and then. If not just add it later when it is available. In the short term adding the hugel-wood is likely to be far more important (along with compost, mulch etc...) and your sandy soil sound like it is very short on organic material. Biochar is not a substitute for this.

Again, I'd like to point out that context may be most important factor.  Florida (semi-tropical) and Kent (temperate) have very different soil bases and climates.  I believe that in semi-tropical conditions, organic material decomposes, volatilizes, disappears etc much, much more  rapidly than in cooler temperate soils, which is why anthropologists thought no large populations could ever have arisen in the Amazonian jungles.  Then they discovered signs that maybe they did.... and found terra preta!  This 'black soil' (which is also found elsewhere) PRESERVES the nutrients that are provided by the short-lived organics... often for CENTURIES.  And in drier areas, it also holds water (not a problem in temperate Kent, I don't think).   So it may be critical to use biochar to modify the base constituents of the soil itself (this is not fertilizing), most effectively when a bed is first constructed, and one has easy access to deeper levels of the soil.  (I believe the nutrients from organic material can work into the soil, via decomposition and microbial action over time, when just layered on top, as in mulching and sporadic chop-drop, etc.  

Also, there is a difference between gardening acreage and a city lot... different strategies for different sizes : )

Couple thoughts I haven't seen yet.

Not sure you want to mix everything you are talking about together, seems like the clay should mostly be a base layer to help hold all the good stuff in place on top of it.  I've done the clean briquette method, it will start to smell quickly, two weeks is probably overkill for soaking in urine.  Also not sure you need to charge the biochar so well before putting it in the ground.  It's a high surface area substrate so it will act like a filter and charge itself over time.  Plus the biology will consume some stuff from it and leave other stuff behind.  If you can find a source of top soil with more clay in it that would probably be good too, both under the biochar and other compost type stuff you add, plus on top to get a nice thick soil layer.  I think most hugels end up with too little dirt so having some decent soil to add on top will be good as well.  Mostly I'd suggest layering, with the clay on the bottom (or most of it below whatever mix you come up with) And the compost plus other additives on top.  I'd probably mix everything with some free top soil/fill dirt to spread it out more as well, versus having a thin layer of each.  

Looking ahead a bit, perennials with year round roots should help hold the good stuff in place too.

Also, if you are doing three mounds, feel free to experiment and report back.

nancy sutton wrote:Again, I'd like to point out that context may be most important factor.  Florida (semi-tropical) and Kent (temperate) have very different soil bases and climates.  I believe that in semi-tropical conditions, organic material decomposes, volatilizes, disappears etc much, much more  rapidly than in cooler temperate soils, which is why anthropologists thought no large populations could ever have arisen in the Amazonian jungles.  

True that.

But while we are on context, you can also look at lots of other strategies for building poor sandy soils.

We don't have many details of the OP's conditions, but one strategy that has seen great success is using vetiver hedges to build soil. The grass stays in dense hedge rows and doesn't seed. It can be cut a couple of times per year and used as a chop-n-drop mulch. It helps build soil carbon around the root zone, and where the mulch is breaking down, and it prevents surface runoff in storms reducing erosion and sinking rainwater into the soil.


A vetiver hedge planted across a drainage ditch. Vetiver trap sediment and slows flow, while also building soil carbon


I'm trying to highlight that when you have a hammer, everything looks like a nail. Biochar may, or may not, have benefits in this context... but there are lots of options to explore.

Buster Parks wrote:Couple thoughts I haven't seen yet.

Not sure you want to mix everything you are talking about together, seems like the clay should mostly be a base layer to help hold all the good stuff in place on top of it.  I've done the clean briquette method, it will start to smell quickly, two weeks is probably overkill for soaking in urine.  Also not sure you need to charge the biochar so well before putting it in the ground.  It's a high surface area substrate so it will act like a filter and charge itself over time.  Plus the biology will consume some stuff from it and leave other stuff behind.  If you can find a source of top soil with more clay in it that would probably be good too, both under the biochar and other compost type stuff you add, plus on top to get a nice thick soil layer.  I think most hugels end up with too little dirt so having some decent soil to add on top will be good as well.  Mostly I'd suggest layering, with the clay on the bottom (or most of it below whatever mix you come up with) And the compost plus other additives on top.  I'd probably mix everything with some free top soil/fill dirt to spread it out more as well, versus having a thin layer of each.  

Looking ahead a bit, perennials with year round roots should help hold the good stuff in place too.

Also, if you are doing three mounds, feel free to experiment and report back.

Hi Buster! Thanks for all the info. I agree that I might be throwing everything and the kitchen sink when activating the coal but in my defense 1) I’m starting these beds on a surface of white sugar sand with maybe a millimeter of soil covering it. And the weather here means baking sun and torrential monsoon (exaggerating but not by much) that just leach everything out of the soil. And most importantly 2) I’m Latina and that’s just how we cook 🤪🙃🤣
But in all seriousness,( i am going to experiment with the clay, however) do you think there’s a chance of me causing harm or burning the plants? I’ve seen some you tube videos of people with hukel beds in my zone 9A and they have done pretty well, I don’t expect great results from the start and I know everything will reduce. And I will be specially careful to put a good thick layer of top soil and maybe amend with a bit of clay too if Ms. Sutton shares her brand with me

I’m going to use 1 bed for annual greens, bed 2 for mostly tomatoes and peppers and bed 3 for herbs and edible perennials .

Oh and most importantly! Could you please share the name brand of the clean briquettes that you used?

Thanks a million! 🙏

Sure, Vanessa..I suspect you'll find a different brand, but I got 'Paws and Claws' brand, clumping clay (it holds more water than the non-clumping type).  Look for a 'feed/farm' type store, where they sell the cheapest litter, in larger boxes.. for cat kennels, etc.  Also, if you can find a 'drilling supply' outlet, they sell larger bags of the plain clay (it is used to line the holes)... they may have cheaper 'broken' bags.   Also, I think I heard that straight clay + straight sand = concrete, so be sure to mix the clay with organic material, when putting it in the hugel :)  Looks like you have an adventure ahead, and glad that others in your area are succeeding :)

nancy sutton wrote:Sure, Vanessa..I suspect you'll find a different brand, but I got 'Paws and Claws' brand, clumping clay (it holds more water than the non-clumping type).  Look for a 'feed/farm' type store, where they sell the cheapest litter, in larger boxes.. for cat kennels, etc.  Also, if you can find a 'drilling supply' outlet, they sell larger bags of the plain clay (it is used to line the holes)... they may have cheaper 'broken' bags.   Also, I think I heard that straight clay + straight sand = concrete, so be sure to mix the clay with organic material, when putting it in the hugel :)  Looks like you have an adventure ahead, and glad that others in your area are succeeding :)

Thank you my darling! 💐

Vanessa Alarcon wrote:
Hi Buster! Thanks for all the info. I agree that I might be throwing everything and the kitchen sink when activating the coal but in my defense 1) I’m starting these beds on a surface of white sugar sand with maybe a millimeter of soil covering it. And the weather here means baking sun and torrential monsoon (exaggerating but not by much) that just leach everything out of the soil. And most importantly 2) I’m Latina and that’s just how we cook 🤪🙃🤣
But in all seriousness,( i am going to experiment with the clay, however) do you think there’s a chance of me causing harm or burning the plants? I’ve seen some you tube videos of people with hukel beds in my zone 9A and they have done pretty well, I don’t expect great results from the start and I know everything will reduce. And I will be specially careful to put a good thick layer of top soil and maybe amend with a bit of clay too if Ms. Sutton shares her brand with me

I’m going to use 1 bed for annual greens, bed 2 for mostly tomatoes and peppers and bed 3 for herbs and edible perennials .

Oh and most importantly! Could you please share the name brand of the clean briquettes that you used?

Thanks a million! 🙏

I had used the Trader Joes stuff, which someone said earlier in the thread isn't available any more, sorry.  I wouldn't worry too much about burning plants, at worst it will be a temporary effect early on.  I only have a small patch of sand in my yard, but have read how tough it can be to get anything to hang around in it.  That's why I think roots are going to be key for you.  Good luck with it!

Thanks! For anyone else looking at other sources of clean charcoal briquettes, I just found this article. They mention Royal, Stubbs and a new material I wasn’t aware of but I’m eager to do more research on, Coconut husk charcoal.

https://www.foodfirefriends.com/best-charcoal-briquettes/