Composting in the Cold - Indoors and Out

Guest blog by Lisa Howse, SWRC's Compost Education Coordinator

The trees outside my window are turning gold and a chill is back in the air. These crisp fall days have me thinking about the garden. It’s time to dig out those hills of potatoes, pull up the last few carrots, and gather up the browning squash vines. But what about that black plastic bin in the corner of my veggie plot – how should I get my compost ready for the winter?

Composting is a great way to recycle organic scraps that would otherwise be trash, and turn them back into a useful soil additive. The composting process takes advantage of helpful decomposition microbes that are already present in nature to break plant material down into simpler forms. But when the thermometer dips below 0°C, these helpful microbes go into hibernation and the breakdown stops. I don’t want to waste a winter’s worth of nutrient-rich kitchen scraps. What’s a compost enthusiast to do?

As it turns out, there are several good options for continuing to compost in winter. The simplest solution is to stockpile your kitchen scraps (or other organic materials) throughout the frozen winter and just allow the composting process to take over again in spring. As a fan of simplicity, this has usually been my tactic. My kitchen scraps freeze solid in the bin, preventing smells and making them minimally attractive to pests. In fact, the freeze-thaw cycle of winter can help these materials break down quickly once it warms up, as the ice crystals that form within them tears up their internal cell structure and makes them soft and squishy – a process I am reminded of every time I thaw out frozen bananas for a batch of muffins.

If you are going to go this route, there are a couple things to keep in mind. First, the frozen materials will not settle and shrink as they would in a warm compost, so it is easy to run out of space. Unless you have a lot of room available in your outdoor compost, it is best to forego adding fluffy “brown” materials (such as dry leaves) until the spring. If you still run out of room in the main compost, you can place a garbage can, bucket, or other convenient container just outside the back door to store your frozen scraps in the meantime. If your main compost is hard to access in winter – say, situated in the far corner of the backyard with several snowdrifts between it and the house – then using the bucket just outside the backdoor may be more convenient in general. When the snow recedes and the ground thaws, these stockpiled scraps can give your compost a nitrogen-rich boost to get it active again quickly!

Composting Indoors

But all of that still requires braving the snowy outdoors. There are other, entirely-indoor methods of composting that you can practice while staying warm and toasty. (These are also very useful for those with no outdoor space; such as apartment-dwellers or an office building.)

The most well-known of these is arguably vermicomposting. Vermicomposting uses red wiggler worms to eat food scraps and turn them into worm castings. While you can buy a multi-tier worm “tower,” vermicomposting is usually done in a simple Rubbermaid tub with some air-holes punched in it, and filled with a simple bedding of damp newspaper or cardboard. Apple cores and vegetable peels are buried beneath 2-3 inches of bedding every few days, and the worms do the rest.

Some people find the idea of keeping live worms inside messy; I don’t agree. I’d say red wiggler worms are the most elegant form of composting. A well-run worm bin is contained, neat, and smells like nothing but some damp earth. There is also no guesswork involved in when materials are “done;” everything in the bin is clearly either fine-textured worm castings, paper bedding, or fruit. The castings do not need to be harvested until there is no more room to bury food in the bin, and when you do harvest, you can take advantage of the worms’ aversion to light to do most of the work for you. Admittedly, I was a little nervous the first time I took our office bin home to “worm sit.” What if something went wrong? I was not ready to cope with 3,000 angry worm housemates. However, I followed the guidelines from our 4-page factsheet, and everything went fine. The worms were very polite guests; they ate my kitchen scraps without issue and kept mostly to themselves.

A second indoor-method is bokashi fermentation, which is done in a simple 5-gallon bucket. I have not done this yet. I will admit, originally I was turned off by the need to continually purchase inoculated bran, combined with the “snooty,” better-than-thou tone of the first few bokashi articles I encountered. But as I spoke to more friendly, down-to-earth bokashi practitioners, I was won over by the tidy factor, and the ability to process scraps into dirt in as little as 4 weeks. Scraps and bran are added to the bucket until it is full; then it is set aside to ferment for at least 2 weeks – but there is no hurry. The final step of the process is to dig the fermented scraps into the soil somewhere outside, or add them to a traditional outdoor compost bin. However while the outdoors is snowy and white, the sealed buckets can be stored indefinitely without any harm. It may be time for me to look into a bokashi bran supplier and give this process a shot.

Now, the final indoor-composting method I’ve encountered came as quite a surprise. I’ve done a fair amount of information-gathering on compost methods, and the obvious conventional wisdom is always the same: don’t make a compost pile indoors. Surely, I assumed, even a well-managed compost bin (of the non-wormy variety) would create too much mess, drip, and odours for inside. It was up to one of my composting associates to prove me wrong. Following an internet guide, she gamely put together her own small, indoor compost in a large rubber tub. It did have drainage holes in the bottom, and sat upon a drip-tray, but apparently there wasn’t a lot of liquid coming out. The tub itself was layered with shredded paper from her husband’s office, dry potting soil from annual houseplants, and scraps from her kitchen, and topped with the loosely-fitted lid. While she kept the compost in the basement, she said smells had never been an issue and she probably could have kept it upstairs if she had the room. Things were rotting nicely and by spring, she expected to have a couple buckets of good, finished compost.

I was flabbergasted. I guess this simply highlights how easy and inoffensive the composting process can be: mess and smells do not have to be part of the process. With a little care and forethought, you can easily turn organic track into gardening treasure – even in the winter.