These are the continuing voyages of the starship hot heap. Until actually, you know, measuring them, I had blithely assumed my compost bays were about 3 feet in each dimension. This is important as the advice and indeed the evidence is that along with the right mix of materials, at least 3’x3’x3′ is required to ensure the heap reaches and maintains a good temperature. The godfather, the don, of the hot composting technique Robert D Raabe says that
“To prevent heat loss and to build up the amount of heat necessary, a minimum volume of material is essential: a pile at least 36″ x 36″ x 36″ is recommended. If less than 32″, the rapid process will not occur.”
That’s pretty clear. Upon checking my bays I was surprised to find they were not going to cut the mustard, weighing in at a mere 2′ wide, 2’6″ deep and 3′ high, 15 cubic feet in volume. My last two attempts at a hot heap have not fired on all cylinders and I am now wondering if size matters. A week or two back I resolved to fix this by somehow enlarging the bays. After a certain amount of ruminative pencil chewing, I decided that the easiest path to embiggenment was to turn three existing bays into two wider bays by removing the interior walls, and then extending the sides out to give the required depth.
Out came the interior walls.
A handy pallet provided a quick and essy new dividing wall.
I used the wood from the old front door panels to extend the sides to match the new dividing wall.
Finally I made a new front door. I need two, but only had the wood for one. The second can wait, when I turn the heap I’ll just swap the door over.
The converted bays now measure 3’2″x3’9″x3′, or just over 35 cubic feet, well over double the volume of the original bays.
Keen to see if this makes the difference, I spent quite a lot of this weekend ferreting out ingredients and filling the new Bay 1. Being significantly larger, it now takes quite a lot of filling. I collected about 20 bags of spent hops, barley mash, manure, hay (all green) then straw & wood shavings plus a load of cardboard and newspaper (all brown).
Interestingly, contradicting my earlier research, the same godfather of the hot-heap says very clearly that an even 1:1 ratio by volume of green:brown is what’s needed, not the 1:2 ratio I’ve seen elsewhere.
“…experience has shown that mixing equal volumes of green plant material with equal volumes of naturally dry plant material will give approximately a 30/1 carbon to nitrogen (C/N) ratio”
For this heap I have gone with the don.
It occurred to me after filling it that it will also take quite a lot of turning! I am not looking forward to doing that every other day. All good exercise over the Christmas holidays, I suppose.
I’ll be back in a few weeks with tales of temperature profiles and other fascinating compost business.
The Propagator 
Is the 3 X 3 X 3 the minimum size, or is it the optimal size? (I am guessing that by ‘at least’, you mean that it can be bigger.) My concern that if it is not supposed to be bigger, that although three sides and the top are open to the dissipation of warmth, the side that is adjacent to the bin next door would be very insulated while the next bin if full.
Our compost is excellent, but we put almost no work into it. We just pile what we have, toss it over once in a while, and keep it going like that. The piles are quite large, and I do not know what they do inside, but they seem to do it well. The only improvement I would like to make is to label the oldest pile for neighbors who come to take some of it. I sometimes find holes in less evolved piles where some of it was taken.
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3x3x3 is minimum size for this rapid composting technique. Bigger is even better, but harder work to turn. Back hoes are the often used to turn bigger industrial scale heaps. A closed heap is better than an open heap for heat loss but some heat loss is inevitable particularly if the ambient temp is low like now in winter. Your piles are working just fine from the sound of it, probably more slowly, but just fine. Same end result.
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They work remarkably well for the minimal attention they get. I am never there when they get turned. They guy who does it makes very neat work of it. I am only interested in the first and last heaps. I dump horse ‘product’ and coffee grounds on the top heap, and sometimes collect finished material from the bottom heap. On rare occasion, I must collect coarse debris from around the heaps, and toss it onto the first heap.
Pretty soon, we must find more efficient ways of recycling our debris. The compost pile is nice because the neighbors take so much of it. However, we dispose of so much coarse debris that does not get composted. We will be recycling more of it into firewood, but are still at a loss in regard of what to do with all the foliar debris. We dump much of it into ravines, but can only do that away from roadways and residences.
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Won’t the foliar debris compost down?
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It would, but there is just SO much of it. We have many acres of landscaped areas here, and trails than must be maintained through hundreds of acres of forested areas. Redwoods are hundreds of feet tall, so produce tons of debris. It is not practical to compost it all. We tend to be somewhat selective with what gets composted, so that redwood and oak is more often disposed of, but pruning debris from common landscape material gets composted. Too much redwood and oak puts too much tannic acid into the mix. All of it could be composted, but we tend to prioritize that which is easiest to compost. Also, some of the redwood debris is out in the forested areas, so it is easier to toss it aside than drag it out.
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Not a bay enlargement surgery for me … rather a shoulder surgery… (😱…thankfully not yet, just an corticoid injection)
I explain: mine has decreased in temperature since the last time … lack of lack of turns because of tendonitis in the shoulder: it will be for next time!
(PS : everything is fine )
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Ouch, take it easy Fred.
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Take care Fred, tendonitis is very painful. Hope the injection has helped relieve the pain.
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Thank you Jude. Not easy to take pictures with right hand but I’m fine tks.
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My hot heap’s gone cold (25 degrees). Not turned it much though. I will be interested to see how your reboot goes.
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57°c on day 3. Turned it today which has cooled it down to 53°c. I reckon it’ll be above 60°c tomorrow.
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Great idea to use pallets! I only turn about once per week… more frequent is better, I know, but it’s a lot of work!
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Having just turned the larger heap, I agree – it’s a lot of work!
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