Factors affecting the decomposition rate of organic matter include time, temperature, moisture and oxygen levels, and particle size. In winter, air temperature becomes the deciding factor. In the compost pile, microbes responsible for the breakdown of organic matter are still active, even when the temperature drops. The center of the pile can be warm and actively composting because of heat generated by bacteria, but the outer layers are subject to daily highs and lows. Different types of microbes are effective at different temperatures, but the most numerous ones prefer pleasant, balmy weather in the 70 to 90 degree range. How do we insure that the compost pile is providing these conditions when the outside temperature is far from tropical?
Keep the pile moist. It should always be slightly damp, either from added material, rainfall, or water from the hose. If it is too wet, there won't be enough air space in the pile to provide needed oxygen. Another way to aerate, or oxygenate, the pile is to turn it frequently, once every week or two. Shredding the material in the pile to particles less than two inches in size will allow it to heat more uniformly and will insulate it from outside temperature extremes.
What if it's just too cold to get out there and tend the pile? There are alternative methods of composting that would work well in the wintertime. One method involves digging a trench in the garden or flowerbed and adding organic wastes, including kitchen scraps (but no meat, grease, or animal fat), a little at a time, burying the waste after each addition. Another similar way is compost-holing, or digging a one-foot deep hole anywhere in the yard and covering with a board or bricks until full of organic wastes. Remove the cover, shovel dirt over the top, and forget about it! One more way for all those folks with only a balcony or small patio to enjoy the outdoors is to compost in a plastic bin. Get a sturdy one with a tight-fitting lid, add some soil or spent potted plants, and start composting. Stick to vegetable scraps, coffee grounds and tea leaves, shredded paper, egg shells, etc., and you'll have compost for next season's potted annuals.
Tamara Listiak, Smith County Master Gardener
Texas AgriLife Extension Service