Worm hobbyists and organic research centers in Canada and the northern United States lead the way in exploring techniques that permit worm composting in winter. The goal is to set up an enclosed system where the red wiggler worm, Eisenia fetida, can survive by being kept well above freezing. For red wigglers to do their best work, chomping on kitchen scraps, their enclosure needs to somehow stay close to 68 degrees Fahrenheit, notes Glenn Munroe of the Organic Agriculture Centre of Canada.
Set up an outdoor worm compost bin with a volume of at least 1 cubic yard, notes Bentley Christie, a worm hobbyist in Southern Ontario who runs the online sites Red Worm Composting and Compost Guy. This creates the mass needed for the compost to generate its own heat as microbes warm the feed scraps as they decompose. Some worm hobbyists place a 2-inch layer of chopped food over a quarter of the surface area of their worm bin and add loose bedding such as shredded newspapers or cardboard right up to the lid.
Add insulation to the worm bin exterior using bales of hay, thick carpet, 4-by-8 insulating foam boards or the more environmentally friendly alternative, leaves. Pack dry leaves around the top of the bin and hold in place with plastic stapled to the bin lid. Track the temperature via a remote temperature sensor in the bottom of your bin near an area of worm activity. If the worm bin still needs a boost to reach 70 degrees Fahrenheit, heat via a light bulb in a coffee can or water warmed by an aquarium heater and pumped through tubing.
A cinder-block worm bin at below ground level to take advantage of the earth's insulating qualities, covered with a lid of cedar decking, worked well for worm hobbyist Robert Frost of Johnson Creek, Wisconsin. Make sure your outdoor worm bin faces south.
A year-round outdoor system can handle more waste material than an indoor bin and avoids problems, such as fruit fly infestations, of indoor bins, notes Bentley Christie.
The good news about most winter composting plans is that, even in a harsh winter with many days below freezing, the worm cocoons will survive even though the worms may not, tests at the Nova Scotia Agricultural College confirm. And the worms themselves can survive having their bodies partially encased in frozen bedding and will only die when they are no longer able to consume food, Munroe notes.
The worms redistribute themselves within their bin according to temperature gradients, Munroe writes. The worms find a comfortable, sometimes-narrow band of optimal temperature at a proper distance from sources of internal heat from decomposing food, avoiding frigid or too-hot zones in their bin.