Experiment in using biochar as worm bin bedding

I'm starting to use biochar in my landscape. I just built (and am in the process of refining) a biochar stove. So I now have 15 gallons of biochar to charge. In the interests of stacking functions, I decided to use it as the substrate of a worm bin. My theory is that because biochar is both water retentive and good for aeration, won't collapse structurally, and has a huge ability to absorb excess nitrogen, it would be ideal for this purpose and help to prevent a smelly slimy mess.

When the biochar burn in the TLUD stove had finished, I quenched it with a lot of water. Then I put the char in 5 gallon buckets full of water and let them soak overnight. I drained them, and then put them in the future worm bin, which is a rubbermaid tub with holes in the bottom and ventilation in the top, draining into a second tub. I ran some more water through it, and then mixed in some shredded paper. I let the bin sit for a few days, and then buried a handful of kitchen scraps in one corner of the bin, and ran more water through it.

Two days ago, I got some worms from an established worm bin. They came mixed together with a fair amount of bedding; leaves, newspaper, some scraps, and coffee grounds. I'm not sure how many worms are in there, but quite a few. I put the whole mass of bedding and worms in the opposite corner of the bin, in a hole dug into the charcoal/ paper bedding. The surface is covered with a piece of cloth.

Every few days, I will be checking to see if the worms have spread out from their initial corner into the rest of the bin. If they do, it will prove that the charcoal bedding is not toxic or repellant to them. I'll report back on what happens.

If you crush the charcoal into a fine powder, worms will live in it.  I use biochar heavily in my potting mixes and often find worms in there.  They seem to like it just fine  - so long as it is finely ground up and there are nutrients for them to eat.

remember that they cannot eat the charcoal, they need humus as energy, so they cannot live in pure biochar dust.

For what it's worth, I notice that the soil around my biochar trench is always full of worms.  Something about the charred earth brings them to that space.  Maybe dead (cooked) soil organisms?
I've also added biochar to my kitchen worm bin.  The worms seem to tolerate it quite well.  They don't eat it but it makes a good addition to the castings to improve structure.  Same thing with coffee grounds.

I'm interested to know what type of material your biochar is made from.  

I didn't crush the charcoal; maybe I should have. I did break up big chunks. The pieces are smaller then a walnut, maybe hazelnut size. And they contain some fines, of course. If I crushed them up, they would possibly provide less structure, but would provide more surface area.

The charcoal is made from scrap construction lumber and pallets, probably pine. I didn't use anything with paint or nails in it.

I should have specified in the initial post that I'm using redworms.

It would stand to reason that the worms would be good for the biochar, but I don't see anything in the biochar that would be particularly beneficial to the worms.  Or am I missing something?

Worms like decomposing organic material to eat.  Biochar doesn't decompose.  In fact, what small pieces of biochar that actually pass through a worm's digestive tract wouldn't offer much to the worm by way of nutrition.  But it would certainly charge the biochar with all sorts of wonderful enzymes and bacteria.

I could certainly see the benefit of mixing a lot of worm castings with your bio char before using it in your garden, but as worm bedding?  What's in it for the worms?  I'd rather bed them with good organic stuff that they'll eat and poop out, and with a habitat best suited for breeding more worms.

The idea, which has yet to be proved, is that the biochar will be good for the worm bin environment; in theory it would even out water availability, absorb excess nitrogen, and, unlike paper or other bedding, maintain its structural stability over time. In theory, of course! Supposedly it also promotes microbial growth, and red-worms derive most of their nutrition from the microbes, not the food scraps that they incidentally consume.

I've had some slimy, smelly disasters with worm bins in the past, thus the interest in alternatives.

I have added biochar to my wormbin in the past but it never made up all of the bedding. I found that it helped control odors and prevented the bedding from getting too hot when i added a lot of nitrogen rich material like ground flour to help speed up population growth. I got the idea from a youtube video in which the author experimented with adding biochar to the worms feed. He found that adding biochar at a ratio of 50/50 biochar to feed resulted in the fastest consumption. The theory was that the biochar acted as a microbial reef and since composting worms eat microorganisms that have consumed food scraps the protective environment for the microbes resulted in more microbes and more feed for the worms. It worked well for me and seemed to allow me to feed more in a shorter period of time but breaking up the biochar can be a headache.

I dug around in the bin today and found that worms are migrating into the biochar side; so it is working so far. I'll keep you updated on how it works out in the end.

The bin seems to be working well so far. It has not yet ramped up to consuming all of our green waste, but it is getting through about 4 quarts of scraps a week, all of them frozen as a precaution against fruit flies.

I overloaded it a bit at the start, but there were no disastrous consequences or smells; I credit the charcoal's absorptive properties.

Due to a busy schedule, I have not added more bedding in these 2 months, which I probably should have. But even so, the charcoal has maintained its structure and kept things from collapsing into an airless mass.

On the whole, I'm pleased with it. The next big test will be this summer when I try to grow stuff with the resulting compost.

The bin is still working fine. I've managed to kill every other worm bin I've ever had. This bin has had alternating periods of neglect and overloading, which should have been bad for it, and also due to the hot, dry weather I've been unable to burn another batch of charcoal to add to it; but it is still working. I think the charcoal really helped with smoothing out fluctuations in the moisture level, and keeping things from collapsing into an airless mess; it may also have helped to keep odors down. Its just subjective, but the bin seems to smell a lot less then other bins I've had.

Hi Gilbert.

From what I understand of the reasons behind amending with biochar, you shouldn't need to add more unless you remove some from the bin environment. As pointed out earlier, worms might ingest biochar, but as there's nothing of nutritional value for them, and no volatile organic compounds or anything that could break down, except mechanically, I doubt the individual particles would change much, except for being broken down a little in worm digestive tracts and innoculated with goodies from the worms' gut microbiomes.

I am really glad to hear of this. It never occurred to me to use biochar in conjunction with vermicomposting, but as smell has always been the prime detractor indoors, this seems logical. And I would be excited to see  how your biochar worm casting supermix will perform, or is performing. Have you amended anything with it yet that would indicate quality?

-CK

Hello Chris,

You are right; the biochar shows no signs of breaking down. However, I am worried that the continuous additions of egg carton cardboard and vegetable scraps will eventually tip the conditions in an unfavorable direction. This concern may be groundless on my scale, however, as nothing bad seems to have happened so far.

I have not grown anything with the mix yet. I'm planning to do so in a series of potting soil experiments over the next few months.

was the biochar innoculated before?

No, it was not. I was thinking that the biochar would be inoculated by the worm composting process.

Very nice. I usually throw a little biochar into my worm bin. I may just up the amount because A) I feel like my worms aren't keeping up with my scraps and B) I love playing with biochar.

Thanks!

In the case that if bio char is pulverized small enough for the worms to consume it can be beneficial to the worms but not directly related to nutrition but as grit. Would anyone thing this would be true ? Would worms use this for grit ?

When we spread the surface of garden beds with biochar, the worms take mouthfuls of it and go into the soil with it. I've seen photos of an organic kiwifruit orchard where they top dressed about 1-2 cm of biochar, then went back a year later and sunk a spade into the ground. You can see worm burrows lined with black all the way down to 20-25 cm.

I'd say they like the stuff.

That's pretty amazing and encouraging. Worms and biochar are my only two "functioning" soil improvement projects going.

As for grit, I would think yes? I also put sand into my worm bed but I am almost out of sand so maybe I'll just stop. I would say I'd report back but my worms are taking the winter off. As per usual. Ask me again in the fall, hahaha.

Seems to me Mateo is right about the char’s benefit as grit, as well as having similar benefits to digestion it has in livestock. The surface area hosts more beneficial microbes to aid digestion and absorption of nutrients. I think it was Charlie Arnott who described the soil as plants’ digestive system, and this analogue between worms and larger animals makes sense in that paradigm.

I added some big chunky biochar to my worm bins.  Just to sort of break it up.  I don’t harvest it enough and it’s sort of the ultimate lazy project. I figured the charcoal would help keep it from becoming too compacted.  I dig through one of the bins recently, probably 6 months after adding and mixing in a mound of charcoal.  I found a worm had actually gone inside a piece of charcoal, like I often notice they do with husks of avocado or half of an eggshell.  Anyhow, my conclusion is that biochar added to a worm bin can only be a good thing.i don’t think I would finely crush it though, I think the chunkiness of it helps break up compaction and aerate.

Mateo Reyes wrote:In the case that if bio char is pulverized small enough for the worms to consume it can be beneficial to the worms but not directly related to nutrition but as grit. Would anyone thing this would be true ? Would worms use this for grit ?

I’ve kept worms for the last 4 months.
A DIY stacked system with a section full of larger pieces of biochar (2cm max not inoculated) in the bottom section that usually collects leachate.
I’ve also added fine biochar to the bedding (probably about 15% of bedding) from scratch as both a grit, a way to inoculate biochar, and to stabilise smells etc.
It hasn’t caused any problems.

I’ve seen videos of people using a blender and adding biochar to a bin to act as grit.

Thank you for this thread. You inspired me to order some biochar and add it to my worm bins. I also have rabbits, so I'm going to add it to their litter boxes as well. I've added biochar to soil, but it makes so much more sense to me to get it integrated into the system further up the line.

According to this study

https://www.sciencedirect.com/science/article/abs/pii/S0048969719313622#:~:text=Biochar%20addition%20reduces%20the%20concentration%20of%20mesotrione%20in%20the%20Eisenia%20foetida.&text=Effect%20of%20biochar%20on%20soil%20earthworms%20depends%20on%20its%20applicate%20rate.&text=About%201%E2%80%933%25%20of%20biochar,reduces%20mesotrione%20toxicity%20to%20earthworms.&text=About%2010%25%20of%20biochar%20application%20induces%20DNA%20damage.

1-3% biochar in worm compost benefits the worms and 10% causes DNA damage...

That's a very useful study, Kimi.  I have wondered whether I should put some in there.
John S

Kimi Iszikala wrote:

1-3% biochar in worm compost benefits the worms and 10% causes DNA damage...

I make some of my biochar specifically for my worms... out of banana leaves. The leaves are paper thin and so, can be pulverized very easily with a spoon (only slight hyperbole).

I typically make a batch of (food/bedding/etc.) for my worms with about 2 gallons of rabbit poop, a similar mass of shredded paper, a trowel full of my fine biochar, and 2 trowels full of coffee grounds. Now and then I add some scraps. I mix everything well by pouring the mixture back and forth between 5 gallon buckets, and then totally soak in a screened "colander". This "recipe" is working out well for me. I use my smallest biochar specifically so that it will find its way through the worms.

I have been making Johnson-Su/BEAM style compost for a few years now,  and this effectively ends up being an approximately 2cu yard worm bin. After the pile gets back down below 90f, red worms can be added safely and they consume the formerly thermophilic compost. I add 1-2% (3-5gal) of coarse charred hardwood (I do not call it biochar until its inoculated with biota) to the J-Su as I fill it, trying to distribute it throughout.

Instead of a tarp or landscape fabric, then cap the pile with 1/2-1” of charred wood to shield it from light and raindrops, and capture off-gassing nutrients and carbon. I also sprinkle a similar amount around the bottom outside the hardware cloth where the pile drains/leaches nutrients, and worm castings spill out. This eventually forms a little pile of fluffy black goodness that I use for my spring compost tea and extract applications, well before the rest of the pile is ready. I have looked at this under a scope with some students of Dr. Ingham, and it looks excellent (full of fungal hyphae and diverse amoeba and bacteria), though the biochar is like looking into a black hole  The layer of char on top always has worms working away at it, with wild birds looking for them and some char grit, sharing their manure/microbiome as well upon landing and takeoff.

During the last six weeks of anomalous heavy snow, I considered building a stackable flow through worm bin that could be kept close to the kitchen and it could be added to continuously. When I started the design and build though, it occurred to me I would be spending many times the hours to build it, and using much more material than a Johnson-Su. Moreover another J-Su would produce 350-400gal of vermicompost in 12-18months, versus the 10gal I would hope to get every couple months from a stackable bin system. This makes a couple snowshoe trips the Johnson-Su in progress worth it to me.

Either way, as I build more J-Su bins, I will continue to add my charred hardwood end pieces pyrolized in a 2gal cast iron dutch oven in our woodstove, which has been in use this winter a lot.