What is composting and how does it work?
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There’s something so satisfying about turning your would-be waste into something useful. This is part of the allure of composting: You get to witness food scraps that would’ve ended up in the landfill transform into nutrient-rich material and — less visible, but still rewarding — you get to know you’re preventing harmful emissions from warming the planet.
Read on to learn about how to reduce food waste with composting.
What is composting?
Compost is both a verb and a noun. To compost (verb) something is to put it through a natural process of decomposition and create organic matter that can be used as soil amendment. Microbes consume the feedstocks (think, munching on an apple core) and turn them into a stable, high organic matter compost. That nutrient-rich organic matter is also called compost (noun); it can be used to add nutrients back into the soil and help plants grow.
Ways to compost
Whether you have lots of space at home or none at all, the good news is that there are a variety of ways for you to participate in composting.
Compost piles. Backyard composting usually takes the form of a pile, which is built on top of soil and usually enclosed in wood, wire, or cinder blocks. A pile should measure at least one cubic yard.
Compost bins and tumblers. Composting bins or tumblers are fully enclosed containers that can be controlled for certain conditions, like temperature. With a bin composter, you can put your food waste in a self-contained structure that either sits on the ground or is slightly elevated. Using a compost bin can also help speed up the decomposition process because it traps heat and gets hot more quickly.
Vermicomposting. Worm-box composting involves building a worm bin that lives either outside or inside, ranging in size from a shoebox to a twin-sized bed. Whereas other compost methods rely on microbes to break down organic waste, vermicomposting relies on worms to do the heavy lifting. You’ll need to keep worm bins in shaded places between 59 and 77 degrees Fahrenheit, although worms will survive in temperatures as low as 32 degrees and as high as 95 degrees Fahrenheit as long as they have the proper bedding. Worms are also sensitive to too much moisture or too little moisture. They need enough oxygen and don’t like conditions too acidic or too basic.
City-provided curbside collection. We get it — not everyone has a backyard or a lifestyle that allows them to tend to a compost pile. Especially city-dwellers. Some cities, like San Francisco, Austin, and Denver are stepping in to offer curbside pickup for your food scraps, which they send to an industrial composting facility. Your local farmers market may also have a drop off point for food scraps, so that farmers can use them in their compost piles.
How does composting work?
Home composting is the process of turning organic material into soil amendment. Composting essentially assists the natural process of decomposition by creating an ideal environment for decomposing organisms (think: bacteria and worms) to do their work.
There are two primary types of composting: hot and cold. Hot composting relies on the internal temperature of the pile to drive decomposition. It’s the most efficient way to compost, as microbes generate heat as they break down your food scraps and yard trimmings, and that heat helps organic matter break down faster. Hot composting also relies on air flow and water to maintain that ideal microbial environment, which means you have to turn and water the pile to keep the decomposition factory running smoothly.
Cold composting essentially follows the same process as hot composting, but there’s no heat to accelerate the process. With cold composting, you don’t need to manage the pile but it takes a lot longer — we’re talking years, rather than months — to create usable compost.
To compost at home using a pile, bin, or tumbler, you’ll follow these general steps:
Collect the material. Naturally, you will accumulate food scraps for composting over time, but it’s a good idea to start with a bulk of material to kickstart a healthy compost pile. Consider freezing what you plan on composing in the weeks leading up to starting.
Pick a method and a spot. First, decide if you want to have a hot or cold compost pile; then, choose an accessible spot with good drainage, and, if you decide on hot composting, a place that has easy access to a water source.
Start your pile. Build your base with four to six inches of brown material and two inches of green material. From there, continue layering browns and greens with the same ratio.
Build, water and turn (or don’t). If you’re hot composting, you’ll periodically add to your pile, and turn and water it as needed to maintain the moisture level of a damp sponge. If you’re cold composting, you don’t need to turn anything over, but you might consider occasionally using a rake or pitchfork to shake the pile up and get oxygen circulating.
Harvest finished compost. After a few months (or a couple of years if you’re cold composting), you’ll have nutrient-rich, dark, gorgeous compost ready to be used in the garden or on your lawn to help support happy, healthy plants.
Keep adding, keep turning. Composting is an ongoing process — not a one and done. Keep adding to your pile, and continue turning it. If and when the pile gets too high or too big, you can move material to a separate pile, or take a portion out and use it in your garden.
Compost ingredients: greens and browns
A healthy compost pile needs a mix of carbon and nitrogen-rich materials (browns and greens, respectively), plus water and oxygen. For best results, especially with hot composting, you’ll layer two to three parts browns with one part greens.
Browns: Brown materials are the base layer of your compost pile and should be added over every subsequent layer of greens. Browns are carbon-rich materials like twigs, wood chips, dry leaves, coffee filters, and untreated cardboard.
Greens: While most browns are actually brown, nitrogen-rich green materials can be lots of different colors because these are most of your food scraps. Coffee grounds, tea bags, banana peels, old fruits and vegetables, grass clippings — all of these are greens that can be composted.
What not to compost at home
While there’s plenty that can be composted at home, there are a few things you should avoid.
It’s generally not recommended to add animal byproducts to your home pile, including meat, bones, and dairy . Not only can those things attract vermin, but they can also introduce pathogens — which a home pile may not get hot enough to kill. Cooked foods and grease should all be left out to avoid attracting unwanted pests.
If you use a worm-bin to compost, you’ll also want to avoid adding a lot of citrus and onions without other materials, because the acidity can kill your worms.
But here’s a big caveat: If you use a Mill food recycler to preprocess your food scraps, you can compost many of the food products that are otherwise considered no-no’s for your compost pile, including meat and dairy. That’s because Mill heats them enough to kill any potential pathogens and grinds them into nutrient-rich grounds — making them easier to mix into your pile and less noticeable to unwanted visitors.
How to tell when compost is ready and how to use it
In a well-maintained hot compost pile, home compost should be ready in about three to five months. You’ll know it’s ready when it stops heating up after mixing, and there are no visible food scraps left.
If you like, you can sift your compost to remove any large pieces. Once you confirm your compost is ready, you can start spreading it around. You can add it to flower or tree beds, or spread it directly in your lawn or garden.
Composting FAQs
Can I just throw my food scraps in the garden?
It depends on where you live, how big your garden or yard is, and what time of year. But if you have a small space, you shouldn’t throw your food scraps directly into your garden, as this is an invitation for unwanted pests. Adding them to a proper compost pile or tumbler will help them break down faster.
How long does it take to make compost?
Hot compositing, done the right way, can produce usable compost in three to five months. Cold composting can take anywhere from a year to two years.
What’s the best time of year to start a compost pile?
The best time of year to start composting is the moment you feel motivated enough to do it. However, if you’re hoping to be a bit more strategic, depending on where you live, spring and fall both provide excellent conditions for compositing, both in terms of climate and the organic materials (dry leaves in fall, lots of trimmings in spring) needed to start a pile.
Composting made easy
Mill dries and grinds your food scraps overnight into nutrient-rich grounds that can be added to your garden or compost pile.
Sources:
United States Environmental Protection Agency: “Composting at Home.” December 18, 2023. https://www.epa.gov/recycle/composting-home
United States Environmental Protection Agency: “Approaches to Composting.” December 12, 2023. https://www.epa.gov/sustainable-management-food/approaches-composting
Seattle Public Utilities, The Natural Lawn and Garden: “Composting Yard and Food Waste at Home.” December, 2016. https://www.seattle.gov/documents/Departments/SPU/EnvironmentConservation/WastePrevention/CompostingAtHomeGuide.pdf
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