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Hot Compost Not Getting Hot; Is It the High Altitude?


November 8, 2020

I’m glad to have found your site and hope you have some ideas. I’ve been hot composting in Northern California for over 20 years,  taken Elaine Ingham’s course,  and yet I’m stumped by composting here.  Never before coming here has a one of my compost piles reached less than 150, most reach 160 and stay for about 3 days.   My concern was keeping it from getting too hot.

I’m in Trinidad,  Co 81082, and have built about 10 piles now, ~4’x4’x4′ using different materials,  being careful to manage proper moisture,  etc, and the hottest i can get us 140°F for two days. I got to wondering if thermophilic bacteria don’t exist at higher altitudes, or very dry naturally climates.  I’ve wondered about buying a thermophilic inoculant, but always chuckled at them before given hot composting has always been easy for me.  Ideas??


Answer from JZ: Great to hear from Trinidad.  Other colleagues may also respond to your question.

I think that you have well considered the variables in your hot process setup. Actually 140F,  in my opinion is good enough, why this does not maintain beyond 2 days may be related to these variables: 

A.  Air / oxygen: does your pile contain coarse bulking material throughout ? Bulking at regular intervals in a hot pile helps convective air flow a" chimney effect" in the pile, allowing it to “breathe". Hot process is high microbial energy process therefore needing/using oxygen. Heat in the pile comes from microbial enzymatic breaking of the carbohydrates bonds formed in plant photosynthesis.” Fire" burns hotter with oxygen. More microbes, more respiration, more oxygen used. More nitrogen required for rapid microbial proliferation.  See B, below. See our brochure, specifically pp.6-7.:

B. C:N ratio of your mix - try enriching to 1:1 by weight. As you know microbes require nitrogen for reproduction / cell wall formation. You might try making your final pile mix at 50:50.  For every part carbon add an equal part nitrogen for a richer mix.  In which case bulking will be quite helpful to avoid compaction of moist greens.  If few greens are available, then you might consider sprinkling with fish emulsion liquid - directions on the label. Alfalfa meal is another choice. Mixing your shredded greens and browns together before adding to a hot setup is quite helpful as it’s an already blended microbial menu.

C. Ambient air temps in your area may possibly be involved in heat loss from the pile.  A cover “blanket” may be helpful, eg. layers of cardboard.

D. Turning/ churning frequency at your convenience approximately every 7-14 days helps aeration, once the pile has reached  your target temperature.

E. Inoculating the pile to increase microbial proliferation and thereby action, is your choice.

I sprinkle a cup or so of already finished compost, as layers are added, as my inoculant for hot and cold setups.

F. Keep practicing, then you’ll get use to the needs of your area.

What do you think ?   Let us know if you have questions.   Compost on.     Best.

From original questioner: (BTW, my apologies for poor grammar and typos in my original email.  I’m pecking it out on my phone and often miss errors I would normally catch using a keyboard) .

You may have picked up on something with “bulking” to allow more oxygen flow.  It makes sense that composting at 6000ft instead of sea level would require more air FLOW into the pile.  I’ve been building these piles using the same Bearcat shredder with the same screen thus generating the same material size as I did at sea level; it may have worked there, but won’t here.  I’ve never added vent pipes into my pile either.   Could that give the needed increase in air flow here at altitude?

Kinda funny, now that we’re having this conversation, I now remember cycling in Switzerland and seeing their compost baskets always lined with black plastic.   That was contrary to what I had been taught that piles need to breathe.  I wondered if the black plastic helped maintain temperature in their cooler climate,  but always wondered about oxygen input.  Certainly possible they turned their  piles more often, and I don’t know the elevation where I saw these piles.  Anyway,  I just now remembered that observation.

I’m still kinda surprised 140°F is normal for you.   I assure you,  I had to watch my piles to be sure they didn’t go above 160°F.  I would typically turn and add water if I thought they were going higher which would last for maybe one day, and then right back up to 160.  They’d typically stay at 160 for maybe 4-6 days,  and then hover in the 140 range for another 10 days,  and then around 120 for another few weeks.

I still wonder if the 140-160 bacteria simply don’t exist at higher altitudes.  Although I have a microscope for observing microbes present, it never occurred to me when composting at sea level to take a sample during the hottest phase and try to identify those microbes.  Someone must have done this.   What do 150° thermophilic bacteria look like? Fun conversation!

Answer by JZ: Coarse bulking, in my opinion, is a space holder in the pile which keeps it “fluffy” thereby reducing compaction thus allowing allowing upward convective air flow. This would work at most altitudes, though I have not specifically researched that. Any composting setup will generate some heat due to the breakdown of carbohydrates, thus releasing the captured sun energy. Warm air rises thru the pile the – chimney effect.  In a cold process this heat is less noticeable, but for sure in a hot process. (In our website menu, see Convective Airflow under Composting Info.)

As we are high and dry (5.3K elevation) we have to make efforts at keeping moisture in a setup, so our bins are very snug – not many holes. It is the convective effect of bulking which keeps us in good aeration. We also put a drape on top to decrease evaporation. I repurpose a piece of plastic or tarp on top of my setups. It’s just a loose fitting drape. We do line our fence wire bins.  See Wire Fencing Bin in Homemade Bins under Composting Info.

I have not used perforated pipes in my set up, some do that.  I have no experience to comment on that. I’m guessing that plastic pipes themselves would serve as a bulking agent, preventing compaction, thus helping air flow.

Cannot comment on microbial activity at high elevations. You might try a search for “Composting at high altitudes”.

Keep practicing and producing finished compost.    All the best.

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