(Slightly updated 2019-04-08, although the podcast has not been updated to be consistent.)

(This blog post is accompanied by an explanatory podcast. See below.)

Many people compost. It can be easy or hard, depending upon your tolerance for turning and work, and of the Wild Thing who wants a free meal.

I can imagine and have known dogs to get into bins, and racoons supposedly get into them. There’s plenty of photo evidence online of racoon footprints near compost piles and bins, and I have seen muddy footprints of racoons on the outside of ours, but I haven’t found a single online photo of a racoon in a compost bin. Racoons might be hardy, but my wife, Claire, once had a granddog that got into some partly cooked compost and soon developed seizures because the partly digested compost had neurotoxins from microbial activity. This did require expensive hospitalization.

So it’s a good idea to keep your compost bins protected from the stray mammal.

That’s a shot of our twin compost bins. The active one is above. The other is “cooking down” over the winter, and should be ready for garden and yard use by late Spring. We have a New England-style Blue Bin which collects rainwater from our roof and gutter system. We use this almost exclusively to add water to the compost in late Spring, Summer, and Autumn, and wash out pails and implements.

I took out some compost today and, with the handle of the small pitchfork I use, an essential tool for composting, I was able to knock ice away from the interior of the Blue Bin spigot and get free running water:

It is 1st January, after all, in greater Boston, Massachusetts.

This brings me to what I want to primarily write and talk about: How to do winter composting. Happy to share.

First, let’s look at our composting setup:

When Claire and I remodelled our kitchen, we had stainless steel compost bin installed flush with the quartz rock counter. Uncapped, and accompanied by a pail of compost from First Parish Needham, Unitarian Universalist, which we collect from coffee hour there and compost, sharing the chore with friend, Susan McGarvey, it looks like:

Now, there are several sources for composting which claim meats and cheese are unsuitable. I can imagine that, in the case of open compost piles, or extreme quantities, it might be a good idea to keep these out of your compost. But Claire and I are vegetarians, for the most part, we like our cheese, and we have three cats. That means we have scrapes from cat food.

That’s Darla, by the way.

For the most part, we We never trash our bio-organic waste. The exception is the litter from the cat litter boxes. As of March 2019 we also compost the material from our cat litter boxes, a material which is basically shredded walnut shells and stuff the cats contribute. This is done in a self-standing pile of leaves, yard, and garden scraps in our back yard.

During the Summer and warm months, particularly in drought, keeping the compost piles moist is a key goal. When they start developing flies and lots of insects instead of predominantly worms, that means they are too dry. The typical procedure in non-Winter months is

1. Keep the moisture in the compost bucket inside to a minimum.
2. Stir the existing compost well.
3. Add in the new material, stirring lightly.
4. Add water. For us, that’s a full compost pail of the water.
5. Stir the compost briskly, mixing in the water and the new material throughout the pile.

In addition, in other than really hot days, you still should see worms and, often, steam rising from the pile when you first stir it.

Winter is quite different.

No additional water gets added to the compost. However, the pail is rather wet, as I’ll dump excess coffee and soy milk into it, so the compost can, at times, be floating in ambient organic stuff. (I do the dishes, by the way, so I can control this.)

So here are the steps I do. I explain why later and in the podcast. That’s inserted below.

Get organized.

You saw the two compost bins above. The active one always has this extract heavy plastic sheet on it, weighed down by rocks. This is critter deterrent, and it has worked for years. The bins themselves are heavy plastic which resists clawing and chewing. They are actually two balls which, could, in principle, be rolled. But I discovered that that means they can’t be loaded more than halfway, because they are too heavy. So they still next to one another, in place, and I stir them instead.

So Winter composting is really quite different than Summer. In fact, we time things to swap when the leaves come down off the trees. The key point is to keep the compost pile from freezing solid. The only reasonable heat source is the exothermic activity of the microbes cracking and consuming the foodstuffs and organics themselves. In fact, everything about Winter composting is designed to maximize that.

The compost pile begins as a empty contained which is filled with whole leaves. These are compacted a couple of times and topped. Then, an indentation is made in the center of the leaves with the pitchfork, carving out a hole in the middle which will hold the compost. It doesn’t extend to the ground. At least initially, the compost should float on top of leaves, supported by them.

Initially, new compost is added into the hole. About 50-50 compost from an old, existing pile is added to innoculate the new pile with microbes. Leaves are spread atop, and the bin is closed up. And you’re on your way.

Then, it is critical that adding additional new material be done carefully and gently.

Leaves are gently removed from the top of the compost, and pushed to the side. If it is really cold you, you should endeavor to get the task done quickly.

Then, with the pitchfork, plunge into the bolus of compost, and twist it, trying to disturb the compost side to side as little as possible. The idea is you don’t want to break up the clumps of microbes working on that bolus. You want to aerate it, sure. Make sure you reach all parts of the pile, but concentrate on the center. Don’t attempt to stir it aggressively as you would in the Summer. That’ll make the effort a failure, because it’ll freeze.

In fact, when done correctly, the temperature of the compost in the leaves will exceed 60°C. In all likelihood, this will kill off the worms. For Winter composting, that’s fine. We’re interested in the microbes. There’s no danger of fire, because that demands temperatures well above boiling.

Next, add the compost. Here there’s two sources. One came from coffee hour at First Parish, and consists primarily of relatively dry coffee grounds and paper. Add that in first.

Obviously, the plastic bag containing the coffee grounds is left out. As a matter of fact, don’t even attempt to put supposedly compostable plastic bags in a home composting setup, especially in Winter time. These generally don’t break down except in really high temperature industrial composters. And, even then, I wonder.

Next I added in our sloppily wet home compost. The idea is to saturate the relatively dry with this. Do not add additional water. When it gets cold, it’ll freeze into a block of uselessness which will stink like crazy during the Spring thaw.

A critically important step: Take the pitchfork, but do not stir, not even as gently as above. Instead, simply push the forks down through the new material two to three dozen times. The idea is drag up old composting material and microbes through the new material, so to get it well underway before it freezes. The microbes will give off heat, and keep that from happening.

So here’s what it looks like. I’ll sometimes fish a bit of old compost out with the pitchfork and spread atop the new for good measure.

The leaves are scraped back over the compost bolus, and I check to make sure it remains insulated in all directions.

The next step is to close it up, and clean up.

However, today, even though there are no worms in the pile, we have friend visiting, a slug, which, apparently, associated with the oak leaves, has decided that the compost pile is a nice place to hang out during the cold Winter.

I didn’t disturb it and placed it back into the leaves.

I put the two lids atop, the rocks back, and then clean up.

That’s rainwater from our barrel. On days when the barrel is frozen up, I need to plan ahead and take out a pail of preferable warm-to-hot water to help with the cleanup. By the way, here’s a tip on the barrel which is intended to prevent something we encountered last winter. We failed to drain the barrel enough ahead of the deep cold, possibly because of excess rains. And when it frozen, it expanded, and rotated by itself on its vertical axis, making it difficult to direct rainwater and such into it.

Our solution was to deliberately drain it deeply after the new compost bin setup, even if this meant we were wasting rainwater.

What to do with the washed out compost bin’s water, whatever it’s source?

Claire has a row of chipped, composting leaves off to one side of the back yard. I pour the excess water, with its slurry of food, on top of these. In addition to filtering, this helps the microbes in these side composters, yet isn’t enough to attract any animal who really cares.

I’ve seen wintering and migrating Robins, though, poking around these piles. Perhaps they have some worms and other critters, like the slug shown above.

That’s it.

A technical summary: The biochemistry and microbiology of home composting is still largely unexplored. I have been able to find one comprehensive paper:

E. Ermolaev, C. Sundberg, M. Pell, H. Jönsson, “Greenhouse gas emissions from home composting in practice“, Bioresource Technology, 2014, 151, 174-182.

While this paper is titled to suggests its interest is principally greenhouse gas emissions, they actually did a serious dive into what was going on. There are several other papers which emphasize the greenhouse gas emissions of composting:

• S. Brown, C. Kruger, S. Subler, U.S. Composting Council, “Greenhouse gases and the role of composting: A primer for compost producers“, Environment Quality, 37(4), 1396.
• A. Brockaway, “Comparing greenhouse gas emissions from organic waste disposal methods“, Summer 2012.
• A. Sánchez, A. Artola, X. Font, T. Gea, R. Barrena, D. Gabriel, M. Á. Sánchez-Monedero, A. Roig, M. L. Cayuela, C.o Mondini, “Greenhouse Gas from Organic Waste Composting: Emissions and Measurement“, Chapter 2 of CO2 Sequestration, Biofuels and Depollution, E. Lichtfouse, J. Schwarzbauer, D. Robert (eds.), 2015.

There is also this 2003 paper by Kathryn Parent and the American Chemical Society:

K. E. Parent, “Chemistry and Compost“, 2003, American Chemical Society.

And recent paper was indicated:

M.A. Vázquez, M. Soto, “The efficiency of home composting programmes and compost quality“, Waste Management, June 2017, 64, 39-50.