When the weather outside is frightful, can composting still be delightful?
Back in February (2024) we shared a small article about compact cold weather composting strategies. Naturally, it made sense to zone in on vermicomposting and bokashi bins, which are both great options when you want to compost indoors during the winter.
But what about outdoor systems? Are there still ways to compost outside when conditions get extra chilly?
The short answer is: “it depends”.
In this article, we’ll explore various strategies, and constraints, for composting keeners who are eager to process their wastes outside all year long.
It probably won’t be a surprise to anyone reading that the most important factor determining our level of success, by far, is temperature - specifically, the temperature inside our systems.
We’re going to need ways to not only generate enough warmth for decomposition (bare minimum), but also to keep it in!
Before you even think about either of these important topics, though, it’s probably even more important to first decide if you’re aiming to:
A) Have a fully active system going all winter long.
OR
B) Have more of a “slow burn” type of system - one that stays at least partially active, and leaves you a fair bit further along by the time spring rolls around.
We can tell you from experience that Goal A is much more challenging than Goal B!
Especially in any region where winter temperatures are consistently below the freezing mark for at least 2 or 3 months.
And even in milder parts of the country, there probably aren’t too many composters who are eager enough to put in the blood, sweat and tears needed to keep a system going full tilt when the cold weather really settles in.
So, to keep things a bit more simple (and likely more relevant) we’ll be assuming most readers are interested in more of a “slow burn” approach - the type of cold weather composting that still gets results, but doesn’t need to take over your life.
NOTE: It’s worth mentioning that for those of you working with composting worms in your outdoor systems - something we highly recommend - another great reason to ramp up your cold weather composting efforts is that it’s a great way to help ensure that your worm population will survive the winter (especially helpful in colder regions).
Whatever your cold weather composting goals happen to be, there are a handful of topics worth exploring:
- The Importance of System Volume
- Types of Materials (and Their Relative Proportions)
- Insulation - Materials and Structures
- Other Heat Protection/Generation Strategies
The Importance of System Volume
Our number one (natural) way of generating warmth in an outdoor system is virtually always going to be microbial heating. Generally speaking, the more organic matter you heap up - especially if it is a mix in the 25:1 to 30:1 C:N range, with decent porosity - the easier it’s going to be to make that organic matter heat up (and the longer it will likely stay warm).
This is the core concept of thermophilic (“hot”) composting, and something that definitely comes in handy when you are trying to keep an outdoor system going during colder times of year. Bottom-line, your chances of success with a 3 cubic yard heap is always going to be far greater than with a tiny worm bin sitting on your deck! 😉
So, recommendation #1 is to set up cold weather systems that are at least 1 cubic yard in size (ideally, more like 2-6 cu yds).
Types of Materials (and Their Relative Proportions)
Not all organic wastes are created equal, especially when it comes to cold weather composting. Most of us aren’t going to get super scientific with our C:N ratios, so it’s probably more helpful to think in terms of “browns” and “greens” - browns being the carbon-rich materials, like fall leaves and straw, and greens referring to the more nitrogen-rich materials like compostable kitchen wastes, grass clippings and manures.
Generally, if you can aim for a brown-to-green ratio of 2:1 or 3:1 you’ll be good to go. This can be as simple as creating a layered composting system with much thicker brown layers than green layers (making sure all materials are nice and moist).
Beyond the basic categories of materials and their proportions, there are certain types of materials that are particularly helpful when it comes to stimulating microbial heating. Most farmyard manures are great, since they not only contain plenty of nitrogen, but they are also loaded with microorganisms. Similarly, there are a wide range of living materials that can serve as compost activators/accelerators when added to a composting system. E.g. sprinkling in some finished compost or rotten wood chips as you add your main system materials is a great way to ensure lots of beneficial microbes are ending up where they are needed.
One additional possibility worth mentioning is coffee grounds. Even relatively small amounts sprinkled in here and there as you set up your system (similar to living materials) can be a great way to help get things moving in the right direction more quickly. We recommend avoiding large concentrations of grounds, however, since these can actually decrease the effectiveness of your system.
Insulation - Materials and Structures
Generating warmth is critical, but it won’t do us much good if we don’t have any way to keep it in the system! This is where various forms of insulation can come to the rescue. Larger systems just naturally have more insulation value due to the sheer volume of materials - but there are a variety of ways we can optimize our insulation efforts to take our system heat-retention game to the next level!
Loose Insulation Materials - A super simple - yet surprisingly effective - approach for boosting the insulation value of your outdoor systems is to heap lots of loose “browns” over top, and around, your system. Prime examples of these include fall leaves and straw. Leaves in particular can be a great choice in many regions because they tend to be very abundant (and free of charge) around the time it starts getting cold, and they are a great composting material in their own right, so they will end up as part of the process over time (and, of course, they are great to add as a material in the system as well).
One caveat worth mentioning is that leaves can mat together when really wet, greatly reducing air spaces. That being said, during really cold (below freezing) conditions this has the potential to be an asset, since you can end up with a sort of outer shell that’s even better at keeping warmth in.
Speaking of really cold weather…
Snow can be another great option for those who live in regions with heavy winter snowfall. It might seem counterintuitive to add something cold when we are trying to keep in warmth, but you need look no further than Inuit igloos (and childhood snow forts, for that matter) to realize how effective this strategy can be. There is one additional tip to mention here relating to snow - we recommend using some type of tarp or other cover that separates the snow from the system, unless you have literally no plans to try and access the system once the snow has been heaped on top.
One last material worth mentioning is loose soil. While we wouldn’t recommend just burying a composting system in soil (even with a tarp), it can be great for mounding up around the base or even digging a composting system directly into (if you have a big heap of dirt available). We will circle back to the insulation value of soil further down.
Physical Structures - Having some type of wall around your composting mass - especially a wall with excellent insulating properties - can help you keep more heat in. An amazing low-tech option is something like straw or hay bales. There is a reason some people use straw bales in the walls of houses - because they offer great r-value!
Obviously, in the case of composting systems, the structural integrity of these types of natural options will diminish over time (and the costs might add up, especially in regions where straw and hay are fairly expensive), but the added bonus is that you will end up with some pretty amazing material for future composting!
If you want something a bit more permanent, you might consider using construction blocks, bricks, or wood for your walls - ideally some type of double-walled structure, so you can fill the empty space with loose insulation.
In-Ground Systems - A highly effective insulation strategy (for both cold and hot conditions) - is digging your composting system partially or fully into the ground. Earthen walls offer excellent insulation (as touched on earlier), and having at least part of the system positioned below ground can just generally help to moderate temperature fluctuations very effectively - especially when combined with various other strategies discussed in this article.
It is worth noting, however, that the more in-ground a particular system is, the more prone it may be to poor airflow, flooding and other challenges. If you do want to go deep with one of these systems, we recommend considering a 3-walled approach, with a thick false bottom (using something like wood chips or a bulky mulch). Our in-ground walking windrows (one of them shown in the photo below) are a large-scale example of this open-ended, in-ground approach.
Other Heat Protection/Generation Strategies
System Location - Where you set-up your cold weather composting systems can have a major impact on your chances of success, especially in colder regions. Always make sure your systems are in as sheltered a location as possible. Buildings, fences, trees and shrubs can all help to block cold winter winds.
Locations with good sun exposure can offer passive solar heating opportunities - something we’ll look at in the next section.
Tarps & Covers - One extra layer of protection we recommend considering is some form of tarp or similar cover. As an analogy, think about the difference between wearing a fleece jacket, and wearing a fleece jacket with a windbreaker over top, on a cold windy day! Apart from serving as a wind block, tarps can be great for managing precipitation more effectively. In areas with heavy rains tarps can help you avoid your system getting waterlogged, and (as touched on) in areas with heavy snowfall, tarps provide an easy way to still access your systems, if necessary.
Circling back to the topic of passive solar heating, if you secure a construction-grade, clear plastic sheet over a dark coloured tarp, your system should receive a fair amount of extra warmth on sunny days (assuming you are able to keep it in a sunny location). Taking things one step further, setting up a composting system inside a hoop house could help even more.
The Importance of Proper Timing - Exactly when you decide to start your cold weather composting system - and how you time various stages of the set-up process - can have a surprisingly important impact on your chances of success. On the “obvious” end of the spectrum, you will make things a lot easier on yourself if you don’t wait until freezing temperatures and snow flurries arrive! Less obvious, is when and how to time things prior to the really cold weather settling in.
Unfortunately, there are no hard and fast rules that will apply to every situation, but one key recommendation we have is to avoid going “too big” too soon, especially if this is a system with a population of composting worms in it. It can be easy to get caught up in the spirit of fall clean-up - a time when composters can end up with a lot of valuable materials - and be tempted to heap everything up at once in September and early October. This isn’t necessarily a “bad” thing - and it’s safe to say it is better than waiting until there is snow on the ground - but you may end up burning through a lot of your system “fuel” (and creating more heat than you need or want) before the cold weather even arrives.
We definitely recommend getting the ball rolling relatively early, especially in cases where you are building something, digging an in-ground zone etc, but to also stockpile your resources a bit more, and gradually add materials, and protective measures over time.
Final Thoughts
Once gardening season is over and the weather gets cold, many composters are happy to hang up their garden forks and leave their outdoor systems as-is until spring. We feel this is a missed opportunity for even more composting fun - and progress!
With a surprisingly small amount of extra time, effort and materials, it’s possible (in many parts of Canada) to not only extend your composting season significantly, but to actually keep outdoor systems going in “slow burn” mode all winter long - helping you enjoy a major jumpstart on your spring composting season!
Summing Up
- Outdoor cold weather composting is possible (and encouraged), but there are some important limiting factors to consider, and recommendations that can greatly increase your chances of success.
- There is a huge difference between keeping a composting system fully active (and accessible) all winter and just building a system that will slowly chug along and give you a big headstart on your spring composting efforts.
- It’s important to have a large enough volume (ideally 2+ cu yds) of the right types of materials in order to stimulate and sustain microbial heating, but the only way to retain this warmth is with some form (ideally multiple forms) of insulation.
- 3 great ways to insulate your systems include: 1) using large quantities of loose “browns” as a thick cover, 2) building actual insulation walls for your systems and 3) setting your systems partially or fully down in the ground.
- Putting your cold weather systems in a well-protected location, and using various types of tarps and covers can also greatly assist your efforts.
- Employing as many of these strategies as you can will only increase your chances of success with cold weather composting!
- For anyone vermicomposting outdoors, these cold weather composting strategies offer a great way to help ensure that your worm population survives the winter.
Helpful Related Resources
Compact Cold-Weather Composting Options
Bedding - The Most Important Material in Your Worm Bin?
Setting Up Your GeoBin for Worm Composting Success
Can I Add Red Wigglers to My Garden?
Outdoor Vermicomposting 101
What Is “Living Material”?
Layered Composting - A Simple Backyard Method to Build Nutrient and Microbe Rich Compost!
Recommended Products
Red Wigglers
Urbalive In-Ground Worm Composter
GeoBin
pH Buffer Grit
EM Concentrate