Low-Tech Biochar at Wishetwurra Farm: An Experiment in Progress.

Throughout the year, Wishetwurra Farm produces organic material of various sorts. As the seasons go by, we pile it up in an open area near where we park vehicles. We cut brush, prune blueberries and apples, from which we get piles of trimmings. We cut oak, maple, sassafrass, beetlebung, sometimes cedar and pitch pine, for firewood.


All those trees we cut for firewood have smaller branches that have to get hauled and piled. The proprietor of Wishetwurra Farm is responsible for maintaining a quarter of a mile of  wooded road. The road gets pruned back a couple of times a year, and each pruning generates truckloads of branches. When storms topple or break trees, there are still more loads to go to the brush pile. We try to compost most garden residues, but some things, like potato and asparagus tops, squash and tomato vines, which can harbor plant diseases, join the ever-increasing pile.

Hiring someone to come in with a machine to chip this pile of material would cost a pile of something else—a pile of cash. We at Wishetwurra Farm love to shovel piles, but prefer to shovel piles of manure or seaweed. We love organic “input”. But we hate to have piles of money be our “output”. Farming is expensive enough, without spending hundreds of dollars to turn a large pile of brush into a smaller pile of chips.

So each year, in the late winter or early spring, when conditions are right, we set aside a day to burn the brush. Massachusetts allows open burning during this time of year. In our town, and almost anywhere, you need tell someone if you’re going to burn. Here, we call the fire chief for approval. He’ll say yes, if conditions are favorable.  “It’s OK.”, says Manny, “But be sure to have your fire out by 4PM”.

The first year we burned our brush pile, three o’clock came around, and there was still a very large pile of hot coals. What to do? I had assumed that the burn would end with a nice pile of ashes, to put on the garden, but time was running out. There were a lot of metal trash cans around, so I hastily shoveled all the coals into the cans. I covered the embers with a thin layer of dirt, which I wet down, and then put the lids on the cans. From time to time I’d spray the cans, since they were hot. Then I watered down the burn site, finishing just in time, as the Chief came by at four, to be sure the fire was out.

The next morning, I discovered that I had eight cans of charcoal. What to do with eight cans of charcoal?

Some research indicated that eight cans of charcoal might actually be a good thing, maybe even better than the ashes I’d originally intended to make. Charcoal, it seemed was now called “bio char”, and was a major component of the legendary “terra preta” soils of the Amazon, soils which have maintained their fertility for over a thousand years.

Incorporated into to the soil, charcoal has a long list of potential benefits. It is said to improve soil structure, to provide a matrix upon which beneficial organisms can grow, to retain water, to aid in prevention or control of soil and foliar borne plant diseases. Biochar is the new cure-all for what ails the gardener’s dirt.

An additional benefit of bio char was that the charcoal “sequesters” carbon, removing it from the atmosphere. If you think that removing CO2 from the atmosphere is a good thing, then putting your charcoal into your garden starts to look like a really good thing to do. The plants take the CO2 from the air, you turn that CO2 into a solid, and put it where it will stay out of our atmosphere for a long, long time to come.

So, because of having to put a fire out by four PM, I became a “convert” to bio char. There are a lot of very, very good minds working on the bio char “problem”. These minds are considering bio char from many angles, from high tech to low tech. Here at Wishetwurra Farm, we like tech, but the lower the better. We’re also lazy, in certain ways.

So, here is the Report on Bio Char at Wishetwurra Farm. With pictures. It’s an experiment, a work-in-progress, so “how it’s done” is likely to change over time. Suggestions are welcome.

You have got to be careful with fire. We burn on the mineral “soil” of our parking area, which is a safe distance from the house, but is close enough to run a couple of hose lines to. If we have not had a recent rain or snow, we use the hose to keep the area around the fire damped down. Shovels, rakes, wheelbarrows, trash cans, etc. are all readied before burning. Having extra hands makes the work easier, and can save the day if there’s ever an emergency. If you’ve got a cell phone, keep it in your pocket, or at least have it nearby, where you can get to it quickly.

I usually start with a “log-cabin” style stacked platform of scrap lumber, to give the fire some good early air circulation. This year I had an old, falling apart wastebasket, which I filled loosely with wood chips. I put a small splash of gasoline on the chips. (Remember: be careful!) Then started piling brush, using the deadest, driest pieces at hand. Then I lit the chips with a long match.


The fire has been burning for about two minutes.

When piling brush on the fire, I like to place the thick ends to the center of the pile, and twig ends to the outside. This way the thick stuff burns sooner, and more completely.


Butt ends in the center, twigs to the outside.

As the fire settles in, we start hauling branches.


In the next photo, notice the important tool?

The hose.


In the next photo, the fire has been burning for some hours. Notice the accumulating pile of embers in the center.


As we get to the end of the branches, there are still many loose twigs, and piles of leaves around. We rake these up, and on to the pile of embers.


This stage usually lasts an hour or so. The leaves are damp, and I think what happens here is that they shut off oxygen supply in the center of the pile, which in turn helps with the charcoal-making.


Eventually, the heat dries the leaves, and they burn, too. At this stage, there are still some larger chunks of wood, which get moved together, so they’ll finish burning. The chunks aren’t charcoal yet.


Then I’ll let the pile sit for another hour or so. It’s a good time to sit in a chair and just watch. After a solid break, it’s time to get the trash cans assembled, and to start shoveling the embers into the cans. A flat-bladed “transfer” shovel works much better than a regular digging shovel. A metal snow shovel might work well, also.


There are always more chunks of less-burned material that get uncovered…these pieces get put together at the edge of the pile, to finish burning.


As the cans get filled, the embers get a spray of water before the lid goes on the can. IMG_6783

I hose down the filled cans, to cool them off.


A slightly better view of the “chunk” pile.


The swirls of smoke and steam are fun.




All the cans are full and there are still a lot of embers left.


The solution is to wet these embers with the hose until they’re out, and to wheel them over to the garden.


Once that’s done, the burn site is thoroughly hosed down, until steam no longer rises from the earth.


I will check the cans periodically, to be sure they’re cooling and not re-igniting. That can happen if any of your cans are old and holey. The holes let air in, and the charcoal starts to burn. I had a couple of really old, holey cans, and that’s just what happened. I finally had to put a lot of water into those cans, to drown the embers. Once you’re sure everything’s safe, and not hot, then you can have supper, clean up, and go to bed.

The next couple of photos show the cooled char, spread on garden beds, ready to till in.



As I review this year’s burn, I am thinking that it might make more sense to just rake out the embers, pull out the unburned chunks, and to hose everything down at the end of the burn. That would make for less discomfort shoveling hot coals into cans. They’re really hot to work with. Wetting everything down at this stage would mean you’d know for sure your fire was out, and you wouldn’t have to keep checking those hot cans. You’d take the wet charcoal directly to your garden at the end of the burn. I also suspect that thoroughly wet charcoal might incorporate into the soil more easily.

You can buy bio char if you want. I found one outfit selling 20-quart bags for $24.99, shipping not included. Also available was a 5-gallon pailful, for $129.00. My burn produced between 300 and 400 gallons of charcoal.

You do the math.

That’s the 2013 Bio Char Report from Wishetwurra Farm.

“Footnotes” and URL addresses for you to investigate:

From Albert Bates: http://www.ithaka-journal.net/pflanzenkohle-als-baustoff-fur-optimales-raumklima?lang=en

3 responses to “Low-Tech Biochar at Wishetwurra Farm: An Experiment in Progress.

  1. Like so many great scientific discoveries, (e.g.,penicillin) yours was serendipitous. The skill is to realize what you’ve found, which clearly you did.

  2. I’ve got mountains of prickly ash, buckthorn and other brush that I’d like to turn into char. I think the key here is the anaerobic ‘burning’ in your trash cans: you’re not turning ash into char but ‘charring’ the as-yet-uncombusted (?) biomass. Right? SO . . . how about dumping it into a pit, getting the roaring blaze going then covering it over. Wait. Then dig up the finished char. Do you think that would work? I’d love to find a way to do this without buying a retort or kiln.

    • Bob, Your idea would probably work fine. I’m too lazy to dig a pit, so I just use the serendipitously discovered “wet leaves” method. I’ll bet if you google charcoal making and charcoal making history you’d find useful information.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s