Active composting in winter

By Benjamin Block

 Compost, the dark, crumbly, earthy-smelling material produced by natural decomposers, provides many benefits to gardeners and non-gardeners alike. Converting garden waste, kitchen scraps, and various paper items into compost at home reduces the amount of waste that ends up in landfills and saves households money on garbage fees. Most importantly for gardeners, compost provides a nutrient-filled soil amendment.

“Hot composting” is commonly done by creating a “compost pile” that is a combination of greens (material high in nitrogen) and browns (material high in carbon). The process is pretty simple, given the correct ratio of materials and enough water and oxygen.

Here in Vermont, however, a critical component of composting is missing during our many months of winter: heat. Compost piles generate heat through aerobic decomposition (with oxygen).

Piles with the right combination of greens and browns can exceed 160 degrees Fahrenheit. Compost temperatures depend on several conditions, so different decomposers, including microbes and other critters, do their jobs at various temperatures.

As decomposers use up oxygen, nitrogen, and water at the center of the pile, temperatures begin to drop. In winter, outside temperatures wick heat away from the pile until these decomposers significantly slow down or, if frozen, stop altogether.

So, what options are available to continue composting through the winter and have material ready for spring planting?

Here are some options that may be right for you.

Hot composting: Don’t let winter stop you

Some intrepid gardeners don’t let Mother Nature stop their hot composting. A sufficiently voluminous compost pile, with enough thermal mass as well as insulation, can keep a compost pile warm enough through winter to continue decomposition. The goal is to prevent the center of the pile from freezing, so the warmer you keep the pile, the faster the materials will decompose.

This option requires some experimentation and continual active management. There are examples online of DIY-insulated compost bins. Some commercial options also are available.

Vermicompost: Make friends with worms

If braving the elements to compost is not your idea of fun, indoor vermicomposting may be right for you. Vermicomposting relies on worms (usually red wigglers) to turn kitchen scraps into a compost called “worm castings.”

A small worm colony can munch through a pound of food scraps in a week. There are many commercial containers designed for vermicompost and plenty of online guidance on properly caring for your colony of banana peel-munching buddies.

Bokashi composting: Ferment your scraps

Another indoor-composting option is called “Bokashi composting.” While technically not composting, it is an anaerobic method to break down food scraps. The input material is fermented by bacteria, not decomposed. Beyond everyday food scraps, Bokashi will also process cooked leftovers, meats, and dairy products.

Mix the fermented solids, considered a “pre-compost,” deep into the soil or add them to the compost to finish the decomposition process. Bokashi-specific composters and the starter bacterial inoculant (sometimes called Bokashi bran) are available online.

Cool composting: Take the winter off

Cool composting is a technique where microbes and other decomposers take their time, especially during winter when decomposition slows considerably. You may need to dig snow out of your compost bin to find room for food scraps and other nitrogen-rich materials.

A compost recipe should include browns, so be sure to have easy access to leaves, wood shavings, or other carbon materials to layer with the greens. Come spring, mix them up, and your compost will come alive again.

The first three options will yield soil amendments for spring gardening, whereas a cool composting pile will need warm temperatures to break down winter additions.

Benjamin Block is a UVM Extension Master Gardener Intern from Montpelier.