Composting and making compost piles is often thought of as a Spring-Summer activity. Lots of fresh green materials are available, and that is also when most people are thinking about gardening. But what if I told you that it is not only possible, but easy to build and maintain a steaming Hot Compost Pile in the dead of Winter?
You can hot compost in Winter by making your piles much larger and using alternative green materials. Also, reducing the turning frequency to no more than once per week. And finally we can keep our temperatures up by continually feeding the pile when we turning it, until we notice that the brown materials are mostly decomposed.
Now, for a regular backyard compost pile in freezing conditions, don’t expect to be reaching temperatures of 150F! Our goal is to keep the pile active so it doesn’t freeze. And we can do it by following a few basic principles.
I live in Pennsylvania, where it gets plenty cold from November through March. And during that timeframe I will build and finish around two compost piles each Winter. This isn’t some ‘listicle’ blog post on tips for Winter Composting. I’m actually going to show you how to do it. Consider it a documentary of why it is harder to compost in Winter, and how to actually make a hot, active compost pile in the freezing dead of Winter. Every picture or video you see is of my piles in my backyard. This is not some ‘curated’ guide using stock images. I don’t just ‘write’ about gardening, I really do it. Below is the proof:
In this article I will go through the step by step process of what you need to do in order to successfully build a hot, active compost pile that will be ready for curing in around two months from construction.
In this article:
- Principles of composting
- Why is it harder to compost in Winter
- What do you need to do different to compost in Winter
- How to build a hot compost pile in Winter
- Can I hot compost in Winter with a tumbler?
- Final Thoughts
- Appendix – My recipe for winter compost piles
Principles of composting
As I have described in other articles and guides, an active compost pile needs four basic ingredients
During the warm season, if you have those four basic ingredients and make a decent sized pile roughly 3′ diameter and tall, you will have active bacteria that turn those materials into useable compost, quickly. In turn, the bacteria generate heat, and as a pile gets hotter and hotter some bacteria go dormant, only to be replaced by different kinds of bacteria. A properly balanced compost pile will go through several temperature phases. 
If your pile is too small, then too much heat will escape and the process will slow down….so, size and temperature are just as important as having a balanced pile with green/brown ingredients.
Why is it harder to compost in Winter
It is more challenging to compost in Winter because more of the heat generated from a compost pile will escape to the outside environment. This is just simple physics following the laws of thermodynamics. The larger the difference in temperature, the faster the energy will leave the hot part (center of the pile) to exit to the environment (cold outdoors).
Colder temperatures will slow down the bacterial and microorganism activity in your pile, which means the microbes will generate less heat. So, it is a negative feedback loop. As the Winter gets colder, more heat leaves, which means less bacteria activity, and less heat generated….lowering the pile temperature, and so on. A cold compost pile in Winter can completely freeze solid.
Also, certain types of bacteria only become active at various temperature ranges. The higher temperature ranges mean that plant material and tough fibers/lignin will break down faster. By not reaching those in Winter, it can seem that our piles aren’t doing much of anything, as decomposition will be much slower.
What do you need to do differently to hot compost in Winter
To make a hot compost pile in Winter, we need to make four changes to our process. Following these four steps is the secret for how to speed up composting in Winter.
- Make your pile larger by around 50%. For example instead of 3′ diameter, make your pile 4-5′ diameter. I’ve made piles 6′ diameter, or small windrows.
- Use alternate green materials, and make sure you can source them / store them until ready to build the pile. Be aggressive about obtaining them.
- Only turn your pile once per week in Winter to make sure heat isn’t lost unnecessarily
- Continue to add green material to your pile each week (kitchen scraps / coffee grounds) to help keep the temperature up
Let’s dive into these principles more deeply
1 – How large your compost pile should be in Winter
My typical ‘summer’ compost pile is about 3′ diameter (minimum). That size is more than enough to reach very high temperatures. But in the Winter, the outside air regularly gets below freezing. So, I make a larger pile.
By having a larger pile, it will be better insulated against the outside air temperatures, allowing the center of the pile to reach and sustain a higher temperature. This is actually based in physics, and we all pretty much know this intuitively. Just think of your home, if you have more insulation in your attic, you will have less heat escape. We have the same principle in Winter composting.
So, make your Winter compost pile 50% larger than a Summer pile. If you live colder than zone 4, perhaps you need to go larger. The determining factor will be that you can always turn the entire pile. It helps to have 360 degree access to be able to turn it.
One other tip, this may be particularly useful to those in zone 4 or 5 – you can tarp your pile to better trap heat. I’m in zone 6 and find this unnecessary, but those who live where the temperature can dip to 20F below may need to do this to help insulate the pile.
2 – Alternate green materials for Winter compost piles
In the Summer, one of the absolute best green materials that is packed with Nitrogen is grass clippings. They get very hot, and I can easily make a pile 140F when they are my primary green material. But in the winter, my grass doesn’t grow. So what can I do? Use alternative green materials.
There are 3 alternative green materials available to most home composters, and I’m going to cover all three and how I use them to make a hot pile.
It’s time to stop emptying counter top compost buckets into the pile, and switch to a 5 gallon bucket with sealable lid. Yup – you guessed it. Store your kitchen scraps in 5 gallon buckets with lids, and keep them outside or in an unheated garage or shed to slow their decomposition.
They buckets and lids can be purchased for less than $10 at big-box stores. The lids keep any stink inside the bucket. Storing 5-10 gallons of kitchen scraps over a week or two is a great way to accumulate a lot of green materials.
I keep two 5-gallon buckets in my unheated garage, or on my back deck. The lower temperatures slows any decomposition/rotting inside the bucket (which is nasty). Then, once a week I can add 5 gallons to a pile, which infuses a bunch of Nitrogen rich kitchen scraps into my active pile, helping keep the temperature up. This is a simple, effective strategy available to everyone.
For new piles, I save up at least10 gallons kitchen scraps while accumulating other materials. Note, the night before I am going to use a 5 gallon bucket of kitchen scraps, I will bring it into the house and set the bucket on a heat vent (with lid sealed!). This will help raise the temperature of the scraps, and it is better to add warm material to a compost pile in Winter.
Used Halloween pumpkins / Jack-O-Lanterns
Halloween pumpkins / Jack-o-lanterns are one of the best green materials for Winter composting. There is a large supply and they are packed with nitrogen. Accumulating 20-40 pumpkins or jack-o-lanterns can give you a very hot pile in short order!
This is one of the *best* green materials for a Fall compost pile. Usually a week or two after Halloween people start putting out their used pumpkins for the trash. If you are driving by and see them, stop and pick them up. I put the word out to my neighbors that I want their used pumpkins, and usually end up with 20-40.
Collecting old pumpkins can be a bit messy sometimes. So, if you keep a trash bag or large plastic tote in your car you can avoid any mess. Some of these pumpkins may be pretty ‘soft’. But, they will still decompose very quickly and give your pile a big boost of nitrogen.
I chop up the pumpkins with a machete before making the pile. But a large knife or even a shovel will work as well.
Coffee grounds from Starbucks
Most of you reading this are probably familiar with coffee grounds being a good compost ingredient. But in Winter when lots of green materials are ‘scarce’ did you know that you can make a hot pile with coffee grounds as your primary compost ingredient? Well, now you do.
It turns out that Starbucks coffee shops (they seem to be everywhere) have a policy to make used coffee grounds available to customers for use in their gardens. I have built hot piles using around 10 bags of used coffee grounds from Starbucks, along with 5-10 gallons of kitchen scraps as my green materials. You can do this too.
When it comes to carbon rich or brown materials, the only difference for Winter composting we need to consider is our temperatures. Since we won’t be reaching the threshold for killing weed seeds of 130F-140F, we need to keep weed seeds out of our piles. That means we need to remove any seed heads from yard waste before adding it to the compost pile.
3 – Continue to add green materials to keep the temperature up
In an active compost pile, you first construct the pile with all of your ingredients. The temperature abruptly rises to 105F-150F, and will then sustain itself within that range for approximately one week. During that time, as the green material rapidly decomposes the pile will compress on itself, squeezing out all the oxygen. With the absence of oxygen, anaerobic bacteria will start to increase, which does not generate heat, thus lowering the temperature of the pile. When this occurs, you normally just need to go mix the pile up to reaerate it, and the aerobic bacteria will become dominant again, raising the temperature. 
In the Winter, when temperatures are very cold outside, the temperature of your pile may drop precipitously. If the temperature gets too cold, no amount of mixing/aerating will raise the temperature, as the concentration of ‘green’ material has dropped. If the temperature can’t reach 50-70F, then the brown materials will basically stop being broken down.
To prevent your pile from freezing, you should ‘recharge’ the pile with additional green material when you perform your weekly mixing. Continue to recharge the pile with more greens until the overall pile (as examined when mixing) looks 75%-90% broken down. Then you can stop adding greens, and just continue to mix.
Also, if during a session when you are adding green material you should pay attention to the level of brown. It is a good idea to add some brown at the same time. This will help the pile insulate itself as well as keep it balanced.
Note – I’ve thoroughly documented two Winter compost piles in the Appendix. It is a timeline of ingredients and temperature of the pile. It shows with great detail how I kept active piles during the freezing cold Pennsylvania winters.
Since we all continue to eat vegetables and fruit during the Winter, you should be storing your kitchen scraps for adding to your pile continually to help keep the temperature warm enough so the entire pile doesn’t freeze. Supplementing this with some coffee grounds from Starbucks will also help keep the center of the pile warm enough for the bacteria to work on the brown materials.
4- How frequently you should turn a Winter pile
During the summer I turn my compost pile every 2-7 days depending on the materials I used. If I used grass clippings, I may turn the pile every 24 hours to prevent it from ‘matting’ up.
For Winter composting, you should turn your pile every 7-14 days, once you’ve accumulated a substantial amount of green material to add. This will allow the pile to stay aerated, but still conserve heat due to less frequent turning. When you do go turn your pile, you may add any kitchen scraps you currently have on hand to help ‘charge’ the pile with more greens.
How to build a hot compost pile in Winter
To build a hot compost pile in Winter, simply accumulate enough green and brown material to make a large pile at least 4-6′ diameter and as tall as it will mound up. The limiting factor is your ability to turn the pile with a pitch fork or potato fork. For extra large piles, you can turn them from each side or make a windrow.
You need to accumulate enough green material to build a large pile in one session. This is necessary to give the microbes enough insulation from a large pile so that they can generate heat without losing it to the elements too quickly.
The day before you are going to construct your pile, you should move all of your ‘green’ ingredients into your home. For example, I will usually stock pile two 5-gallon buckets with kitchen scraps in my cold garage. But, I bring both buckets inside to warm up the day before. That way when I go to build the pile, my ingredients are 60-70F, which will mean more bacteria activity than if they were cold from being stored in my garage.
To actually construct the pile, you layer and mix the pile until you have exhausted your green materials, trying to keep a 50/50 ratio. Now, don’t get too hung up on this ratio just do your best to hit 50/50.
Managing a compost pile in Winter
If you live in freezing temperatures, when the temperature of the pile begins to drop from ingredients decomposing, it can happen quickly. So, as previously stated we need to add more green materials when we perform our weekly mixing. This will help keep our temperature warm enough for the bacteria to decompose our pile.
To see exactly what I did, jump to the appendix. I document two Winter compost piles I made from the initial pile construction, to the dates I mixed and added more green ingredients (with rough quantities). Also I report what the temperature in the center of the pile was at the time of mixing. This should give you a great idea of what you can do to continue composting in Winter.
Once the overall ingredients appear to be broken down by 75%-90%, you can stop adding greens. The compost is about to enter the curing process, which will take some time. But continue to turn it weekly until the pile has the consistency and aroma of freshly dug dirt.
What if my pile freezes?
It is entirely common for the outside layer of an active compost pile to freeze while the center remains warmer. I frequently will have the outer 2-3″ of my piles freeze while the center remains 60-80F.
However, if your pile freezes solid you have a couple of options. The first is to get several gallons of hot water and pour it on your pile. This will instantly thaw out the pile and raise the temperature. Just be sure that you have plenty of greens to add so that the pile has more ‘fuel’.
The second option is to not worry about it, and either continue to dump your kitchen scraps on your pile knowing that when outdoor temperatures warm up you will just have that much more green material to use. If you are worried about stray animals, then you can also use a large curbside trash can for storage until you are able to rework your pile. That will keep animals away from your pile while allowing you to create a stockpile of greens.
Once we’ve stopped adding new green material to our compost, we aren’t totally done. The compost is going to enter the curing phase, where many more biological transformations occur. Continue to turn your pile weekly if possible (not frozen). We will continue to do this until the compost is finished.
Curing compost freezing
Eventually your pile may completely freeze, as we are no longer adding green ‘fuel’ to the pile. And that is ok. Since we are in the curing process, everything will just stop until temperatures warm up.
In late Winter / early Spring the temperatures will begin to warm up, and you should go mix the pile at that time.
When is the Winter Compost pile finished?
Continue to mix it and maintain some moisture until the compost truly looks like crumbly (yet clumping) dirt, and smells like freshly dug dirt. At this point the compost is ready to use in the garden or yard. You can till it into your garden, top-dress your garden or yard, or even just mix it in when backfilling with new plants.
How much work is it to compost in Winter?
In my experience, it takes the same amount of effort to compost in Winter as it does during Spring and Summer. The ingredients all need to be gathered and prepped, and the pile needs to be turned and tended too. The main difference is you have to start out with more ingredients for a Winter pile.
Video Guide to Winter Composting
Below is a video we released on the overall Winter Composting process. It is quite long, but contains all info from this article. It even has an additional 15 minutes of footage documenting two Winter piles from start to finish, with ‘off the cuff’ commentary from yours truly.
Can I compost in Winter with a tumbler?
There are many compost bins and tumblers available for purchase on the market. But it may be difficult to get enough volume of material to generate enough heat. As stated in the beginning of this article, you need to make compost piles bigger in Winter. The same principle applies to tumblers.
However, tumblers do have one major advantage over outdoor piles – their are enclosed, and generally black in color. The enclosure will help insulate the pile and reduce heat loss, acting as a small layer of insulation. And the black color can help absorb sunlight, thereby keeping the bin/tumbler active longer.
Just because plants have stopped growing outside in Winter doesn’t mean we have to give up composting. By utilizing a few simple principals we can keep and maintain an active compost pile all Winter that will be ready for use come Spring.
Simply put, we need to make our piles larger and use alternative green materials as grass clippings aren’t available in Winter. We also need to reduce our turning frequency of the pile to avoid losing heat. And finally, when we do turn our pile (during the active phase) we should continually recharge it with green materials to help maintain that microbial heat factory in the center of the pile!
Winter Composting may sound like a misnomer but is not only possible, it allows you to get a bit of exercise while preparing one of the best garden soil amendments possible. Additionally it allows you to reduce landfill space as well as gaining a more thorough and complete understanding of the principles of composting.
Appendix – a recipe and timeline of my Winter Compost piles
Below is full documentation of my two Winter compost piles from 2021/2022. It contains the dates, ingredients added, and the internal pile temperatures.
2021 Winter Compost pile #1
My first Winter Pile should probably be called my ‘Autumn’ pile, as it was made in Autumn. None the less, the primary ‘green’ ingredient of this pile are pumpkins and kitchen scraps. Pumpkins are an unsung hero of composting, in that they break down lightning quick in a pile. This allows you rapid temperature rise and quick decomposition of everything.
|Date||Ingredient||Quantity||Pile Temp.||Outside Ground Temp|
|21NOV21||Kitchen Scraps||10 gallons (40L)||–||42F|
|Pumpkins||~16 regular sized pumpkins|
|Yard Waste||4 trash bags (flower trimmings / grass clippings)|
|Sawdust||Approximately 50 gallons|
|29NOV21||Pumpkins||6 full sized jack-o-lanterns and misc. gourds||104F||38F|
|Kitchen Scraps||5 gallons|
|09DEC21||6 Pumpkins and a few gourds||98F||39F|
|Final Mixing of pile. It was mostly decomposed. Left to cure.|
Here is a photo of pile #1 on 14DEC2021 – note that it is basically decomposed. Pumpkins are an amazing ‘green’ material. Basically any ‘fleshy’ fruit or vegetable like melon rinds, squashes, or peppers break down ridiculously quick.
2021-2022 Winter Compost pile #2
My second compost pile of the 2021/2022 Winter was constructed in the ‘dead’ of Winter just after the new year. Starting outdoor temperature was just above freezing, and it dipped to single digits multiple times.
Note that all temperature measurements were done with an infrared temp gun. So, the temperature I’m reporting is not going to be completely accurate. The true temperature inside the pile should be somewhat higher. This is because the temperature of the interior surface drops instantaneously when I ‘flip’ it to get my measurement.
|Date||Ingredient||Quantity||Pile Temp||Outside Ground Temp|
|03JAN22||Kitchen Scraps||10 Gallons (40 L)||–||28F|
|Starbucks Coffee Grounds||(4-5 gallons) 3 silver bags, 1 large ‘toddy’ bag|
|Pumpkins||5 Pumpkins / Jack-O-Lanterns|
|Egg cartons, saw dust||Enough to match the kitchen scraps/coffee grounds by volume|
|06JAN22||Kitchen Scraps||1 Gallon (my countertop compost bucket)||83F||17F|
|Coffee grounds||1 gallon (Starbucks silver bag)|
|08JAN22||No additional material added this day. I just wanted to check temp as the snow had melted on the pile.||88F||18F|
|15JAN||Kitchen Scraps||5 gallons||61F||22F|
|Coffee Grounds||5 gallons (Starbucks silver bags)|
|23JAN||Kitchen Scraps||5 gallons||56F||18F|
|Coffee Grounds||4 gallons (Starbucks silver bags)|
|30JAN||Kitchen Scraps||5 gallons||85F||20F|
|Coffee Grounds||3 gallons (Starbucks silver bags)|
|06FEB||Kitchen Scraps||5 gallons||93F||18F|
|Coffee Grounds||9 gallons (7 silver bags, two large plastic bags from Starbucks)|
|Egg cartons||One large brown paper bag|
|13FEB||Temperature of pile = 107F||107F||27F|
|27FEB||Temperatuer of pile = 101F||101F||39F|
|06MAR||Kitchen Scraps||5 gallons||111F||50F|
|Brown plant materials||One large brown paper bag|
|Coffee grounds||2 gallons (two large silver Starbucks bags)|
|13MAR||Kitchen Scraps||5 gallons||74F||27F|
|19MAR||No additions – curing/turning||84F||57F|
|27MAR||No additions – curing/turning||95F||42f|
 – Graves, Robert E, Hattemer, Gwendolyn M, Stettler, Donald, Krider, James N. National Engineering Handbook, Part 637 Environmental Engineering, Chapter 2 Composting. pp87.
- Cullen, Mark, Johnson, Lorraine. The Urban/Suburban Composter: The Complete Guide To Backyard, Balcony, And Apartment Composting. New York : St. Martin’s Press, 1994, pp155
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