This story was originally published in October 2020.
Composting is a great way to return minerals from waste back into the earth. However, composting is a hot process that requires the activity of microorganisms in order to create the byproduct that is useful in gardens. When it gets cold, especially the kind of cold we get up here in Maine, it is more difficult to compost — but not impossible, if you follow a few simple steps.
“Backyard composting during the winter months in New England is definitely challenging,” said Anna Mello, office manager at Garbage to Garden, a curbside composting service based in Portland. “Most home composters do not have large piles; this leads to the piles freezing.”
Here are some tips to maintaining your composting habit throughout the cold winter months.
In the winter, you need to make sure your compost pile isn’t too big or too small.
“Most compost piles that are less than one cubic yard in volume will tend to freeze solid and they don’t have a ton of activity in the winter,” said Mark King, organics management specialist at the Maine Department of Environmental Protection.
King uses lobster trap wire, about 12 feet long by 4 feet wide, and turns it into a cylinder by overlapping and locking the edges. He uses that to trap the compost together.
“By keeping it together, it holds it in a mass that maintains its heat,” King said. “Because the squares are about an inch in diameter all the way around, it has 100 percent aeration which is really beneficial to the compost process.”
To cover or not to cover
It might seem like a good idea to cover piles as a windbreak or to keep excess moisture from getting in, but it’s not required. A large, activity compost pile will be able to withstand the winter weather without this protection.
“If the compost pile is at temperature, it will melt away the snow that piles on top of it,” said Davis Saltonstall, co-owner of ScrapDogs Community Compost in Rockland. “It won’t melt everything around the sides, but it will at least melt the top. If it doesn’t melt the snow, it’s probably cold or frozen, in which case you can continue adding to it and try to get your pile back to temperature. Trying to make sure you have consistent access to the pile is the key.”
If you are concerned about insulation for the hot activity, you could consider a cover.
“In terms of insulators, black tarps can help as they conduct more heat from the sun than the average blue tarp,” Mello said. “That being said, the best insulator is more compost! The bigger the pile, the more likely that the core will stay warm.”
In fact, King said, it is better not to cover the pile for aeration.
“A plastic tarp that won’t let air pass through will kill the activity,” King said. “Tarps are no good, wrapping it with plastic is no good. Trust in the size of the pile and allow mother nature to do its thing.”
There are breathable tarps available on the market, but they are not usually appropriate for small-scale composters.
“If you keep it covered with a tarp that’s a big, impervious, non-breathable surface, it’s likely you’re going to create an anaerobic environment for bacteria,” Saltonstall said. “It’s hard to find breathable covers for compost piles, but there are some out there. Not many of the homesteaders reading this will be at that scale.”
If you are composting indoors, say in a greenhouse, make sure the area has proper ventilation, as carbon dioxide, a byproduct of composting, can be a breathing hazard.
Be pickier with your materials
Though you do not have to change the ratio of green to brown material in your compost pile during the winter — you should still add two parts green materials for every one part brown — there are certain materials you should avoid composting in the wintertime, particularly liquids.
“Any moisture is going to try to rob heat away from the compost pile,” King said. “Anything liquid is a no-no in the winter. Anything that’s putrescible, which means it breaks down quickly, is probably going to be odorous if it doesn’t get absorbed.”
Other materials will help aid the process. Horse manure, King said, is like fuel for compost piles.
“That stuff’s got super energy,” he said. “That pile stays hot all winter long due to all the energy that the horse manure has.”
Sawdust will also keep moisture levels down in your winter compost pile during the winter, which can be helpful to keeping it healthy and active. Ashes, however, are a little more finicky.
“The key to ashes is to put very little in your compost,” King said. “They change the pH quickly. Higher pHs can make conditions unfavorable for microbes. We would suggest not more than a two gallon pail for the whole winter.”
Turn when you can
Make sure you are turning your compost pile whenever possible to promote microbial activity.
“Microbes aren’t mobile,” King said. “Turn it and mix it to redistribute where the organisms are in the food.”
When you expose your pile to add material, King said to make the exposure as minimal as possible especially if it’s a cold windy day. Take advantage of warmer days to get out and turn your compost.
“If a mid-winter thaw occurs, it is best to take advantage and turn your pile if possible,” Mello said. “While the pile may remain frozen for many months, you can still keep adding to it, come spring it will break down.”
The right tools will also help. There are tools that might make winter composting a little easier for you. Large compost piles — about five cubic yards or more, King said — would benefit from having a garden tractor to turn them. King also recommended using a spade fork, which is a “pitchfork, but has a handle like a shovel.”
“That’s probably the best tool that someone can get if they want to bust stuff up in the wintertime,” King said.
However, King said to skip the compost tumbler for winter composting.
“Those things are notorious for freezing solid, [though people have] proven me wrong, by turning it every day to agitate it and it doesn’t freeze,” King said.
Most importantly though, if you commit to winter composting, don’t be deterred by freezing.
“The most important part is if it freezes solid don’t give up,” King said. “There are days that are warmer that will thaw it. Bust into it and wake it up again even if there’s snow on the ground and it’s going to snow again.”