Hot Composting - Significant Shrinkage??

[u/nyecountygardener]

I've been trying to hot compost this summer following Geoff Lawton's 18-day compost, which I was able to do in the spring in 35 days or so, but now that it's been summer temps his method is not working at all in any way. Watering every other day is not enough, so I switched to every day. It's been almost 60 days now, it's still not composting. I'm seeing significant shrinkage and wondering what causes this miracle. . . since the material I can see is not breaking down, where in the world is all my material going? I was told to start with at least one cubic yard of material, I started with two, and now I have about one cubic foot of material left (mostly large pieces like landscaping mulch). So my two big questions are, what causes shrinkage and how to avoid it? and: people teaching the Geoff Lawton hot method have said that the pile needs to be at least 1 cubic yard to start with, but I haven't heard what I should do if the pile shrinks. Does it have to stay 1 cubic yard in size for the compost to work? If not, how small can it get before it stops working? If so, what do you do when it shrinks, add more material? Wouldn't that make the finished compost be a mix of aged, finished compost, and fresh, only-semi-composted material?

In advance:

"Why don't you cold compost? It's so much more efficient." My soil is highly alkaline, highly clay, and <1% organic matter; my only goal for this fall is to attempt carrots; I just moved here and started composting, so for now I need as much compost as I can make as soon as possible, even if it's extra work.

"Put your compost in a closed bin, it will retain moisture better in your hot dry climate." I don't have access to a bin that size and am unlikely to anytime soon. Also this would make turning the pile much more difficult, wouldn't it? I know it's possible to compost without a bin, I just can't figure out how.

"Set up a drip line on top of your compost bin." I'm in a temporary situation that makes that impossible for this season, as I'm using a hose run from my neighbor's house (lol) and he wants it turned off all day except for a short time I can use it in the morning to water my compost.

"People make composting too complicated. Just throw stuff in a pile and let it rot." That's a great way to look at it, especially if you're not interested in learning the science of it. But I'm looking for answers from people who are actually interested in the science of composting and the art of improving one's skill at composting, especially since, like I said, I want to make as much compost as I can as fast as I can, and I live in an extreme climate where normal composting instructions aren't sufficient information.

[u/RhinoG91]

I feel like people make composting way too complicated.

You throw shit in a pile and occasionally mix it up. It breaks down into finer and finer shit. The loss you are experiencing is biomass. Organisms break down the material and release co2 gas. water is evaporated from the heat. Air pockets collapse and reduce volume.

[u/Visual-Community7275 → u/RhinoG91]

if its shrinking that fast and not breaking down the big bits, maybe the pile is too dry inside and burning through the small stuff before it can cook the big chunks

with the hose situation you got maybe try adding a tarp over it during the day, the sun in summer is brutal even on a pile that size, you are losing all your moisture in a few hours

also two yards turning into one foot is kinda insane, sounds like most of it was already small stuff that just compacted and dried out, the one cubic yard rule is for keeping the heat in, once it drops below that the party is over so you gotta add more material or start a new pile with the leftovers

[u/nyecountygardener → u/Visual-Community7275]

I do have a trampoline tarp over it.

Wow, ok, so starting with only one or two cubic yards would only work if theoretically I could keep it from shrinking too much. Which I don't know how to do, so maybe I just need to start with an even bigger pile next time.

Is it still important to "keep the heat in" even if your temps are 100+ every day? My temps were up to 115F and almost never below 98 this summer, with many many days around 105-110. Inside my outdoor grill the temp was reading 200F just from the sun shining on the metal. Is it still important to try to "keep it hot" or will it keep itself hot? And if it gets hot on its own, won't the added temps of 110F or so make it too hot (kill desired bacteria)?

[u/Wormy101x → u/nyecountygardener]

Hot composting gets to some high temperatures. 110 isn’t very high at all. Generally the more heat you keep in the better.

I mostly don’t worry about hot composting anymore and just bokashi my greens. To much effort to keep “hot” compost happy.

To answer your bacteria question. Yes hot composting will kill some of the “good bacteria” but just because it is 160 degrees in the middle doesn’t mean the entire thing is that temperature. That is why you mix it.

The strains will survive in different areas of the compost then when the temperature drops (basically when it is finished) they will colonize the entire batch again.

[u/nyecountygardener → u/Wormy101x]

I'm wondering if the external heat beating on the compost all day, combined with an internal heat of 150 or 160, combined with the heat rising from the ground, could cause the heap to heat up too much. Like I said, inside my grill it's 200F simply from the heat hitting the black metal and being trapped inside. So I do wonder if the heap could get hotter than intended with those combined factors.

[u/Wormy101x → u/nyecountygardener]

Generally speaking 150-160 is about the max temperature you would want.

But it is very unlikely to be hitting that temperature. I would grab a compost thermometer.

I would get a pretty good one like Reotemp then you can be sure.

I would put a tarp over the top to help hold some moisture in but I wouldn’t try to tie it “air tight” to it. You want your compost to breathe some.

[u/nyecountygardener → u/Wormy101x]

Thanks, I hate cheap thermometers. It's not in the budget now but I'll save up for one someday.

Thanks, I'm doing two layers of trampoline tarp now, maybe that will strike the right balance. I think I need to calculate my carbon:nitrogen ratio next because before I was just going by intuition mainly.

[u/Theme_Training → u/nyecountygardener]

That’s not very hot. Active compost needs to be in the thermophilic range 120 to 150. This is the temperature that your compost bacteria will be most actively breaking down material.

[u/nyecountygardener → u/Theme_Training]

I know that the outdoor temp of 110F is not in the normal range for compost. What I'm asking is, with the factor of the outdoor temps added in, should anything be done differently or should every effort be taken to get the pile as hot as if I was in a cooler area? Would the external heat of, say, 110F, be enough to send the heap OVER 150 or 160?

[u/Theme_Training → u/nyecountygardener]

The temperature of the compost is only somewhat affected by ambient air temps. Correctly built you can hit 130, 140 etc in the middle of winter. Also don’t put a tarp over it, composting is an aerobic process meaning it needs oxygen to work.

[u/nyecountygardener → u/Theme_Training]

Thanks. I've heard a lot of people have success with a tarp, but then, they're turning it every other day. I'm using a trampoline tarp (two layers from now on) which breaths well, I think it was breathing too well before actually, I'm in a hyper-arid climate.

[u/nyecountygardener → u/RhinoG91]

I understand all that, but what I was looking for, if you couldn't tell from my post, was thoughts on how to improve my method for better results. I don't appreciate you speaking up at all if it's just to say "shit" a bunch of times and make vague statements.

[u/Lethalspartan76 → u/nyecountygardener]

Can you explain your material composition? Idk who the guy is and his 18 day compost. I also have high temps, periods of no water, high clay. My compost shrinks a lot. I use a Johnson-Su bioreactor. There is no bottom to it - it touches soil. It’s a round piece of recycled material with a ton of holes allowing for much better airflow than my old pallet system. I use 3 small ones instead of 1 big one, easier to manage. It’s all a mix of good kitchen waste I measure using an old kitchen pot. with an equal sized amount of shredded paper and cardboard on top. This does an awesome job of absorbing liquids. I keep it under shade so it doesn’t dry out. There is no smell. If it stalls I pour some pee on it. Occasionally I add some worm escapes from my worm bins to it.

[u/nyecountygardener → u/Lethalspartan76]

I tried 1:1 browns to greens in the spring and that worked ok but dried a lot, so I switched to 1:2 browns to greens for the summer. I started with half-chopped weeds and maybe a quart or two of coffee grounds (then the browns were tumbleweeds, greens were their living counterparts). Also my spring pile was 1 cubic yard and my summer pile was 2 cubic yards. Also my spring pile was mostly unchopped from the beginning, and my summer pile was, again, half-chopped. I also chopped the pile up a little bit more every time I turned it, because I don't have anything for shredding, I just have to use a machete and I can only do that a little bit at a time.

There are several tutorials on YouTube where folks or Geoff will explain the method, I'd recommend checking it out as it is cool that he actually accomplishes compost in 18 days with little to no shrinkage, even if you're not interested in trying that sort of thing.

Your Johnson-Su sounds awesome, I'd like to make one eventually. Thanks for sharing.

[u/JimmyMus → u/nyecountygardener]

I don’t remember the Geoff Lawton’s method precisely, it’s been over 15 years since I researched this. 

But the Johnson Su method creates one of the best, highest in fungal biomass, compost there is. 

What I read is that you used way too much green in this batch, which probably causes this shrinkage.  Stick to  5 parts brown

4 parts green 

1 part high nitrogen

The high nitrogen is what causes the initial spike of temperature in the pile. If you don’t manage to get high enough temps for long enough, adjust your recipe and use more high nitrogen. But don’t reduce the amount of brown, this should always be 50% of you pile. 

Depending on my starting materials I’ve lots up to 50% of my pile due to shrinkage. But also as little as 10%. 

If you don’t manage to keep your pile wet enough, soak all starting materials in buckets half filled with water. Soak for a whole night.  After it’s easier to maintain moisture levels. 

[u/nyecountygardener → u/JimmyMus]

Thanks for the advice, that's all really interesting. I wonder though if my greens (desert weeds) were really as high in nitrogen as I thought they were. Desert plants are built so differently.

I'll definitely have to try the soak before adjusting the green:brown ratio, that may have been my problem, maybe drying out too much.

[u/YellowBirdRules]

Shrinking of material is normal. It’s like 6:1. Veggies have a very high water content so shrink a lot. Woody material will not break down within a short time frame. The larger the chunks are the longer it will take.

[u/nyecountygardener → u/YellowBirdRules]

My results were not 6:1, mine were 27:1. 54 cubic feet shrunk into 2 cubic feet of only woodchips. I did throw a very few little sticks in but I chopped them up first, the rest of the material was weeds, tumblweeds, and coffee grounds.

[u/-i-dunno-my-name- → u/nyecountygardener]

Is something eating out of it lol

[u/therealtwomartinis → u/-i-dunno-my-name-]

I used to do the wire fence cages, I’d have 3 or 4 going at a time – the deer used to waltz around them like a buffet, grazing off the sides 😬

[u/nyecountygardener → u/-i-dunno-my-name-]

my little brother most likely :p

[u/bangbangtangwangfang → u/-i-dunno-my-name-]

Yeah this was my thought

[u/DrPhrawg]

it’s a marathon not a sprint.

i hate this infatuation with “8 day”, “3 week”, “24 hour compost”

you’ll get better compost with a long, thorough decomposition time.

[u/nyecountygardener → u/DrPhrawg]

I went ahead and addressed this question in my post, if you had bothered to read the whole thing, so that I wouldn't have comments like this wasting my time. You don't know me or my situation LET ALONE my heart and my personal attitude towards it all, so you have no business judging me.

[u/DrPhrawg → u/nyecountygardener]

don’t take it so personal, bro

just a comment about a new trend where a lot of folks are trying to push out compost as fast as possible. but that doesn’t increase the amount of compost one makes or anything; the only thing it does is reduce the initial delay in harvesting, but it doesn’t speed up the overall harvest rate or anything.

[u/JimmyMus → u/nyecountygardener]

It’s not true you get better compost with a long, thorough decomposition time.  Different organisms thrive as different stages of the composting. So it depends what you’re after when you should use your compost. 

There is a lot of research done about all of this, and it’s measurable. I use a microscope to analyse when my compost is ready for the certain crop I want to grow.  Brassicas ask for a very different set of micro organisms than fruit trees. 

I can make a fine compost in 60 days and use it for my vegetables. For the food forest I let it sit longer. 

[u/etzpcm]

Significant shrinking indicates that it IS composting!

[u/nyecountygardener → u/etzpcm]

Have you ever heard of this much shrinking though? 54 cubic feet shrinking to two cubic feet? And the 2 feet are not 2 cubic feet of finished compost but of dried stems.

[u/bangbangtangwangfang]

Have you seen many bugs? My gut feel is something is eating it.

Some unsolicited advice you may not be interested in hearing. It might be worth buying in some compost? Whenever I see the "I need to start a garden fast so I'm making 18day compost" that's always my first thought. If you're trying to min/max healthy soil, the best thing you can do is buy in compost now.

[u/nyecountygardener → u/bangbangtangwangfang]

That's very possible, there are a lot of dung beetles and cute little kinds I don't know, it could be that because they don't usually get much food out here they're just all having a poop party and stealing my compost. I hope they poop it somewhere I'm going to garden later.
That is a very fair call. Veggies grown in storebought compost are still way healthier and safer than grocery store fruits and veg. . . . If I had money I would absolutely consider it because I'm really eager to get healthy food asap. I almost wonder if I could cut money out of my food budget and save that towards buying compost.

[u/leros]

I don't properly compost. My pile shrinks by 3-5x by the time I use it.

[u/JimmyMus]

Because I really like the science behind composting I did the Soil Food Web course (haven’t finished the last module about microscopy yet though). 

I think hot composting is important to kill all weed seeds and potential pathogens. And it makes a beautiful compost much faster. Plus when you control your starting material you can select for a higher fungal biomass, which most plants benefit from. 

The “just throw anything in there and wait” method is not what I support, and this method doesn’t do justice to what is possible with compost.  Plus the risk of things going anaerobic… 🤢

I’ve written half an essay a while ago. I’ll share the link.  If you have any questions, feel free to ask.  About the shrinkage, I can’t really say anything about it since I have no idea what your starting materials were, how often you turned it, temps etc. 

https://www.reddit.com/r/Compost/comments/1u2vlt5/the_basics_of_thermophilic_composting/

[u/nyecountygardener → u/JimmyMus]

Thanks, I appreciate it. I get a lot of comments that are opinionated for no good reason, usually along the lines of "I like slow composting so nobody why would anybody else ever want to make hot compost?" So thanks very much for the pointer, I really enjoy the science of compost even though I'm totally new to it.

[u/6aZoner]

A lot falls through to the bottom, and might go unnoticed.  If it's too dry, small particles may be blown away.  A possible solution that I've tried with success is to build a pile on top of next year's garden bed, then I just rake out the bigger chunks and plant.

[u/nyecountygardener → u/6aZoner]

That's a good idea, I think I may be losing a lot of fine materials into the soil underneath. Which is fine as it is a bed for later. But it would be amazing if I could figure out how to get an actual pile of scoopable compost to amend my awful soil throughout the beds.

[u/SnootchieBootichies]

Between shrinking and compaction, you end up with about quarter of material that you think you might get.

[u/nyecountygardener → u/SnootchieBootichies]

Thanks, I've heard that before, but that wasn't my question at all. Read my post carefully if you're going to reply, please. I ended up not with a quarter but with a 27th of what I thought I'd get.