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).

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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.