"Very cold" is very relative - we are down where F and C are getting much closer and no way I'm turning a pile then.

Personally I'd leave your pile to cook along until the pile temp starts heading closer to ambient temperature and then decide. But then I'm pretty lazy; if you want to get the compost done as quick as possible, you might want to turn as soon as it starts heading dramatically down.

But if it's minus 20 (in C or F) you're not going to get quick composting anyway and save your energy.

From my experience, green parts of compost have "cooked" immedietly when freezed. So it 's a good point in the composting process. When frost is over, turning will help to distribute cooked N over uncooked C.

Yeah, it's a good point (although not sure I understand your term cooked) - I don't worry about freezing and turning in our climate - actual freezing and thawing does some of the work of breaking down cells for decomposition. So turning when it's all thawed works pretty well.

Stuff with more C and drier - woody waste, brown leaves - less impacted by freeze/thaw cycle. But then, I think those typically decomposed in cooler parts of the composting cycle (i.e. mostly don't expect them to heat up) and take longer anyway.

Thanks for the suggestions, especially to maybe not turn until the pile temperature starts dropping dramatically. And the idea that the freeze/thaw cycle itself may facilitate decomposition is intriguing.

In addition to wondering if I should turn the pile, I realized today that my pile was too wet as drops of water were dripping out of my hand as I squeezed a handful. It was also a bit sour-smelling, possibly from the use of spent brewers grain as the nitrogen source. I had several plastic containers of shredded cardboard stored in the house so I mixed that in to the pile to dry it out, and as I did that I decided to throw caution to the wind and also turned the top half of the pile. That went fine and was easy enough.

The high temps were in the lower 40s today and the lows won't even be below freezing for the next few days, so I'll check the pile in a day or two to see if the compost temperature climbs back up to 120° as it was before I turned it (crossing my fingers). If it doesn't, I suppose it'll be a good lesson learned.

If it's overall above freezing and your pile is good-sized (as you describe above), it won't be a big problem - with the natural insulation of the pile (i.e. size), if the conditions are right, it'll heat up and stay there for a while.

Mind, I'm pretty lazy with my piles - I'm in a cold climate and let cold composting and worms do the work for me. I just don't find the extra work makes that much of a difference - at least compared to having more piles and more material, and so I'd prefer to maximizing stuff rather than the throughput. (All within limits of my patience and laziness)

But it's definitely true that once the spring thaw comes, my kitchen piles will break down really fast - at least by volume. But I still don't expect them to be 'done' in two weeks or anything. And I'm happy using stuff for mulch so don't need it to be perfectly decomposed.

Every winter the compost bin gets really, really close to being too full and then spring or a temporary thaw comes - some years more full than others - but so far it always works out and some space in the bin opens up.

Thanks, armoured and annpat. I'm pleased to report that two days after I turned the top half of the pile, and added shredded cardboard to dry the pile, the temperature in the center of the pile at least has gone up from 120° to 130° and the sour smell is mostly gone. Very pleased to see that. So either the turning was beneficial in introducing more air, or adding the shredded cardboard did it by...well, introducing more air, or both.

Would I have experienced the same results had this been a normal December/January rather than the climate-crisis December/January it clearly is (lows above freezing for four days straight)? I don't know.

Would I have experienced the same results if I'd turned the entire pile rather than only the top half ? Another thing I don't know.

Damn, creating and maintaining a compost pile is a hell of a lot of fun and deeply satisfying. I've been a gardener for six years and until this year never bothered doing it partly out of laziness but in part because I didn't realize what an incredible experience it is. To witness the transformation of the various materials from your food and garden and Amazon boxes into another physical and chemical form through the help of these amazing, mysterious microbes and the heat they generate is just plain magic. Alchemy, really.

Isnt it? It takes up so much of my time, I barely have any for gardening.

Hah - I could see myself heading in that direction at some point.

Btw, what do you use as your nitrogen-rich ingredients during late fall and winter?

In the fall, I heavily depend on pumpkins and seaweed, but food scraps and garden clean-up are big, too. In the winter, it's almost all food scraps, but, really, they just sit there, frozen, until they break down into slime. I bet I could flip my piles today if I wanted to. 34.5 F

Once the leaves and any fall clean-up are done, my compost is mostly kitchen scraps too. I tend to add some cardboard over winter so it won't be just slime once it thaws, but probably insufficient to hit any desired C:N ratio. When the thaw comes I'll put a thick-ish layer of leaves on top to deal with any smells.

The pile is a worm hotel though and I doubt they give a damn what the ratio is either.

Dang, but I really need an additional pile/an extra bin. The main one is really, really full up this winter.

Any building work going on nearby? Can you filch/negotiate for some pallets?

No one mentioned how the worms might feel about getting disturbed from the center of a nice warm

pile if the outside temperature is 40 degrees or lower. Would they just burrow back to the interior or could they get flash frozen?

I once picked up a stiff clump of newspaper on the ground in Jan. in Maine and found a bunch of frozen Eisenia fetida underneath, which I brought in the house to start a worm bin---with them the founding family. They revived and procreated. That's all I know about frozen worms.

Well, I just spilt out for the pretty bog-standard plastic bin. The main bin is just too too full, and I'm going to be away for a while / off and on, need an easy solution for everyone else. And heck, with long cold winters and a yard with lots of trees, some extra bin space comes in handy.

The other main advantage: we can switch to putting all additions in this new bin and let the old one compost away and age out before emptying it - whenever I get around to it, and no idea when that might be. I've always preferred having multiple bins for ageing anyway, somehow just never got around to it at this place (multiple piles of leaves substituted).

But this year, I finally had to admit that this year I was losing the "we'll have a good thaw soon and the pile will shrink any day now" fight (which always worked out before). With thick packed snow all around, even the occasional warmish days aren't having much effect. And it's no fun having the bin so full that frozen uncomposted stuff sticks to the lid and tumbles out.