In lieu of sending them to the landfill, composting nitrogen-laden food scraps — along with fallen leaves, straw and even cardboard — can pay dividends to you on the farm and to the wider world. That’s because eliminating — or at least reducing — food waste is one of the most meaningful actions we can take to mitigate climate change. In fact, 20% of greenhouse gas emissions from landfills come from food waste.
So, if you don’t currently compost but you could, you definitely should. And if you already have a pile? Ideally, you are encouraging mostly aerobic, rather than anaerobic, decomposition. When carefully tended, a “hot,” oxygen-rich compost pile breaks down in a jiffy. Unfortunately, there are plenty of gardeners who toss their kitchen scraps and garden waste onto the pile but never add water or run a pitchfork through the mess.
Sure, these colder compost piles eventually decompose, but they’ll also release some degree of potentially harmful methane along the way. How much? That depends on the size and contents of your pile.
“Methane is a major contributor to today’s [climate] warming,” says Ilissa Ocko. “It actually contributes more to warming in the short-term than all of the CO emissions that we’re emitting today from fossil fuels.” Ocko is senior climate scientist and the Barbra Streisand Chair of Environmental Studies at the Environmental Defense Fund.
Partly, that’s because methane is itself a heat-trapping gas, and it takes about 10 years to break down in our atmosphere. But even after that methane’s gone? “Ninety percent of the excess heat that is being trapped right now is going into the ocean,” Ocko says. “So, then you get this feedback cycle where a warmer ocean actually emits more carbon dioxide into the atmosphere . ... What ends up happening in that case is that signal ends up lasting for hundreds of years.
“The CO we emit this year — 20% of it will still be there, warming the earth, 1,000 years from now. CO builds up.”
Of course, compared to the methane released from all of our landfills, wastewater, livestock holdings and rice farms, the methane from one small, “cold” compost pile is negligible. But it all adds up — and, besides, with a little vigilance, you can avoid being part of the problem.
As they decompose your banana peels and other organic matter, the bacteria in your compost pile produce methane. If there’s plenty of oxygen in the pile, this methane is further broken down. But what happens without enough oxygen? “The process ends at methane, and the methane is emitted,” Ocko says.
Together, your pile’s size, porosity, moisture content and carbon-to-nitrogen ratio determine whether the organisms in your compost are breaking down matter aerobically or anaerobically. It’s worth noting, too, that no pile is exclusively aerobic or anaerobic all of the time. Different kinds of organisms step up at different stages in order to decompose your raw materials.
Recipes for Success
For best results, your compost pile should occupy at least 1 cubic yard, and it should contain a blend of nitrogen-rich “greens” and carbon-rich “browns.” Technically, the ideal ratio for these is 30 parts carbon for every one-part nitrogen by weight. However, it’s unrealistic to expect perfection. After all, you’ll likely be composting whatever materials you have on hand.
What’s more, each individual material type has its own carbon-to-nitrogen ratio.
For instance, say you have some old straw or fallen leaves to break down. By weight, straw is roughly 100 parts carbon to one-part nitrogen. Dry leaves are approximately 50 parts carbon to one-part nitrogen.
Got grass clippings or leftover kitchen scraps? Grass clippings are about 15 parts nitrogen to one part carbon. And, although they’re highly variable, food scraps are around 20 parts nitrogen to one part carbon.
If you aren’t sure whether you’ve managed to blend a reasonable amount of carbon with nitrogen, your compost will offer up some olfactory clues. A pile that smells strongly of ammonia — think matted grass clippings on a hot day — has too much nitrogen.
Just do your best to include as diverse a mix of compostable materials as possible. And, to ensure more even distribution of heavier, wetter items like melon rinds, chop these before adding them in.
Moisture & Space
Along with its carbon-to-nitrogen ratio, the moisture content and porosity of your compost pile matter, too. Compost should be uniformly moist but not sopping. A pile that is too wet will break down anaerobically. It is also more likely to smell “off.”
To gauge its moisture content, grab a handful of material from the pile and squeeze it in your fist. If more than a few drops of water drip out, the section sampled is probably too wet. If the handful you’re testing feels dry to the touch and nothing drips out? You likely need to add water. To be certain, test more than one section within the pile. If you find a series of alternately wet and dry areas, you might need to more thoroughly mix your ingredients.
And, when it comes to creating space for oxygen to move within and throughout your pile, bulky materials like dried leaves, straw, and even small amounts of shredded paper can be invaluable. So, if after performing the squeeze test you determine that your compost is too waterlogged, you may want to add some of these. Just keep in mind that, because these are typically very carbon-rich, they’ll skew your overall carbon-to-nitrogen ratio.
Running Hot & Cold
Measuring the temperature at the center of your compost pile will further help you to determine whether your pile is likely decomposing aerobically or not. Made with extra-long probes and moisture-proof faces, most compost thermometers are designed to be left in place long-term.
If you’re starting a new pile or recently added or turned your material, the temperature at its core may run anywhere from 80 to 100 degrees Fahrenheit for the first few days. Next, with a respectable carbon-to-nitrogen ratio, adequate moisture and decent airflow, your compost should really heat up. During this “thermophilic” phase, its internal temperature can reach up to 150 degrees. Pile size, makeup and moisture levels will determine how long it stays in this hot state.
An internal temperature that has gone back down to the 80- to 100-degree range may indicate that the center of the pile has become too dry or that it’s time to turn the compost pile. But a change in temperature shouldn’t be your only indicator.
Take a peek at the center of the pile. If it looks dark and crumbly, it may be time to move what’s on the outside edges of the heap to the center and rearrange what’s in the center back out to the edges.
Turn, Turn, Turn?
How often you turn your pile — and the method you use to turn it — also can have a positive or negative environmental impact. For example, to produce compost at scale, many large commercial compost farms rely on fossil fuels to power heavy equipment for shredding and moving raw materials, as well as turning, finishing, and delivering compost. According to Steven Wisbaum, founder of the Vermont-based Champlain Valley Compost Co., “The amount fossil fuel consumed during the various steps of the composting process will impact its ‘net’ carbon footprint.” Obviously, turning your own small pile with a pitchfork and some elbow grease is a zero-emissions activity. Even so, in his work, “In Defense of the Pile Less Turned: A Case for ‘Low-Input’ Composting,” Wisbaum suggests turning too frequently can be counterproductive. “Most of the oxygen added to a pile during turning is used up by the microbial populations within hours, or even minutes of turning,” he writes. “Therefore, unless additional oxygen is being provided under pressure (i.e., via ‘forced aeration’) or a pile is turned hourly, the purpose of turning is not to add oxygen.”
Instead? Turning improves a pile’s porosity. In other words, it creates additional space for oxygen and carbon dioxide to move throughout the compost. “If turning is being done primarily to restore porosity and keep the decomposition process moving at a moderate pace,” he writes, “turning can be timed to occur after internal temperatures have dropped 20 to 30 degrees Fahrenheit from a high of 131 to 145 degrees Fahrenheit.” As you pay close — or closer — attention to your compost, you just may find that you’re generating nutrient-rich compost in a matter of several weeks rather than months. Better still, you’ll have kept all of that material out of your local landfill. And, if you limited methane and carbon release in the process? “Reducing methane emissions is really the key lever to slowing down the rate of warming in the near-term with the benefit of also helping in the long-term,” Ocko says. “And CO is kind of the opposite; it’s the main lever in that, if we reduce emissions of CO, that’s our best chance at having a better climate in the longterm. … They definitely feed off of each other.”