The growing season begins long before the snow melts. At this time of year I am busy ordering seeds, planning the garden, swapping cuttings with other growers, and mapping out the next phases of our nursery and orchard.
Turns out there are others on this land who are also busy in spite of the snow and chilly temperatures. A few weeks ago, friends invited us to go ice fishing and asked if we could bring some worms for bait. I was doubtful they would be accessible in the middle of winter, but figured it was worth opening up one of our fall piles to find out. The worms weren’t nearly as deep as I thought they would be. Just a few inches beneath the frozen surface, red wigglers and earthworms are busily decomposing our kitchen and garden scraps.
Many compost piles freeze solid in the the winter and decomposition comes to a halt until the warmer temperatures of spring. We do a few things differently in our piles to prevent this from happening and to ensure that, come spring, our composts are well broken down and ready for use. Here are a few of my tips for keeping an active compost through a zone 6 winter:
- Bokashi: This is perhaps the most important part of what makes our composts work during cold weather. In the fall and winter we pre-ferment all our kitchen scraps indoors before adding them to our winter compost pile. This allows us to compost all our food scraps including meat, bones, greasy and cooked foods that would otherwise be attractants to bears and other wildlife. It also ensures that there are a ton of “effective microorganisms” in our food scraps before they even hit the pile. Though these microbes thrive in anaerobic environments, I have not found much research on how they survive once they meet the aerobic conditions of the compost pile, especially once the pile heats up (these conditions favour thermophilic, or heat-loving, aerobic bacteria which often kill off other microbes suited to cooler conditions). Regardless, pre-fermenting with bokashi allow us to collect a critical mass of nitrogen-rich food scraps in the winter without it getting stinky, which generate a lot of heat in the compost pile and keep our composts active even in cold conditions.
- We find you don’t need any fancy buckets or equipment to do bokashi – just some bokashi bran, a basic 5 gallon bucket and a sealed lid. We add about 4 litres of raw food scraps to the bucket at a time, sprinkle it with a few tablespoons of bokashi bran, squish with a plate or pot lid to eliminate air (this stage is an anaerobic process) and put the lid on until the next addition.
- Once the bucket is full, we let it sit at room temperature for 2 or more weeks. Usually we have 4 or 5 buckets to add to the compost pile at a time, so this critical mass of biologically active material actually generates it’s own heat and creates a hot compost pile in the middle of winter.
- We’ve also started getting deliveries of raw food scraps from local cafes and restaurants, which we layer in with the bokashi and carbon-rich stump grindings or fine wood chips. Together these materials build up a lot of organic matter.
- Volume: Our compost piles are built using untreated wood pallets tied together with bale twine, lined up in 4 or more in a row. This creates piles that are a cubic metre or more and insulated on the sides, which we find is the minimum size needed to prevent freezing in the centre.
- Insulation: In the fall I line the edges of the pallets with 6-10 inches of straw or dry grass clippings to help insulate the edges of the pile. The top of the pile is covered with more thick, carbon-rich material and a few layers of cardboard to help hold heat in.
- Moisture and Air: Our composts are always covered to prevent getting soggy and anaerobic from rain and snow. Beneficial bacteria and decomposers need air to stay alive and actively decomposing organic matter. I keep piles of woodchips or coarse, dried yard waste beside our composts and add it in layers throughout the winter to help give structure and air pockets to the pile, since flipping it when partially frozen is not an option. Adding this dry material also ensures that the C:N ratio is balanced, as too much nitrogen will cause your compost to stink and not break down.
- Final flip: In early spring, six weeks before I need to use the finished compost, I’ll flip the pile into the empty pallet bin beside it. I aim to get the freshest material to the middle of the new pile, and the aged material around the edges. After that final aging stage, the compost is ready to use right as transplants are going into the ground.
All this combined helps to keep our worms happy and our compost piles breaking down throughout winter. It’s a bit of a hybrid system, part bokashi, part hot composting, part passive (cool) composting, but it works for us. Compost is an essential resource in any organic garden. It’s great to be able to use household food scraps and keep generating more nutrients year-round. I’m looking forward to using this black gold in just a few months.
“It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.”
– Charles Darwin 1881