By Gordon Clark
Extension Master Gardener
University of Vermont
While gardening comes to a stop in the winter, its companion activity, composting, doesn't have to.
While you might think that cold temperatures keep a compost pile from composting, that is not the case. In my winter compost pile I regularly achieve temperatures in excess of 130 degrees F even when it's in the low teens or single digits at night.
I simply charge (or fill) it when temperatures go above freezing, which happens increasingly often in our changing winter climate. According to a study from Climate Central, since 1970 northern New England winters have warmed at an average rate of more than 1 degree F per decade. Burlington, Vermont, has seen the greatest warming of any city in North America with average winter temperatures 7 degrees F higher now than five decades ago.
For winter composting, the major issue is usually the supply of materials, what composters refer to as "browns" (carbon heavy) and "greens" (nitrogen rich). However, there are some uniquely Vermont ways to keep your compost pile charged in the colder months.
GREENS: Since we still eat fresh food in the winter, you will probably always have your own supply of greens in the form of fruit and vegetable scraps for your compost. Don't have enough? You can save up until you do. These food scraps will just freeze harmlessly on your back porch or in your freezer until you're ready to add to the compost pile.
Better yet, ask your neighbors to help, and give them a five-gallon bucket to fill. Local grocery stores may let you take fruit and vegetables they discard, and coffee grounds from the local coffeehouse are another nitrogen-rich "green" to add.
My fun, new find for winter composting greens though is spent beer mash. With a Carbon to Nitrogen (C:N) ratio of about 15:1, depending on the brewing process, spent beer mash is even richer in nitrogen than leafy vegetable wastes, which have a 25:1 C:N ratio. And what does Vermont have if not lots of breweries? Most are happy to give you a few buckets of their spent mash.
BROWNS: If you've already blown through your stored leaf pile, you may be able to purchase straw bales at a local farm or nursery. I have been using sawdust and woodchips, available at local lumber mills and wood shops, for brown matter and have also found these to be superior insulation in cold weather.
I put a nice 6-12-inch ring of these around the interior of my compost bin, and then do my actual composting in the center. This insulation allows me to maintain the pile's temperature, even when it gets cold and even when the pile is considerably smaller than the generally recommended 5-by-5-by-5 foot pile. (My bin is about 4.5 feet in diameter, and the pile has never gotten higher than 3 feet this winter.)
Take note that sawdust and woodchips are extremely high in carbon, having C:N ratios of up to 400:1. You'll want to use them more sparingly in the composting core, mixing them with other browns and/or using extra greens to compensate.
In a nutshell, that's it! Just bear in mind that this is not a method to produce a finished load of fine compost by the first day of spring. What it will do is allow you to keep your microbes alive and healthy during the winter, continue to compost your own food waste and have a fantastic base for when you build the larger pile as the weather warms.
And it allows you to make new friends as you go to your local grocery store, farm or brewery and local mill, lumberyard or wood shop. And what could be more Vermont than that?