When temperatures dip below freezing, you do not have to abandon your composting activities. Although the decomposition process slows considerably in winter, composting is still possible. If the bin is correctly built and prepared for the cold, the interior of your pile will be warm enough to support some biological activity. Continue to add kitchen scraps and small amounts of dried leaves throughout the winter -- once the weather warms up, the pile will begin cooking quickly and you'll have a supply of nutrient-rich humus for the planting season.
Prepare the bin for winter. In late summer or early fall, empty your existing compost bin. If the compost is not ready, consider adding a second bin to use for your pre-winter preparations. Your bin should be at least 36 inches square and 36 inches tall to maintain enough heat.
Insulate the bin. Stack hay bales around the perimeter of the bin, wrap the bin in several layers of corrugated cardboard or secure sheets of high-density foam insulation to the sides and top.
Cover your bin if it does not have a lid. A tarp can be used but a solid cover will be easier when you need to remove snow.
Layer some browns and greens in your empty bin. Browns are dried leaves, twigs and dead plant matter. Greens are things like kitchen scraps and cow manure. Fill the bin about halfway to the top.
Water if needed. The pile should be evenly moist but not soggy. Squeeze a handful of material. It should feel like a wrung-out sponge.
Store some dried fall leaves near the bin if possible. Use a covered garbage can or garbage bag. You'll add these materials to the pile over the winter.
Keep a covered bucket under your kitchen sink. For more effective winter composting, cut scraps into small pieces. When the bucket is full, bring the material out the composter. Put the "greens" in the center of the pile, digging them down in if possible. After a few additions, add a layer of "browns" --- your stored leaves. Continue layering through the winter.
Turn your pile in early spring. Water if needed and continue composting normally.