How to Compost
Learn how to compost kitchen scraps and yard waste at home. Covers what to compost, the right ratio of materials, and how to maintain a bin that does not smell.
We started composting because we felt guilty about how much food we threw away. A banana peel here, coffee grounds there, vegetable scraps from cooking. It all went in the trash and eventually to a landfill, where organic material breaks down without oxygen and generates methane, which EPA calls a powerful greenhouse gas.
The scale is worth knowing. EPA reports that food is the single most common material sent to US landfills, at 24.1% of what goes in. Count yard trimmings, wood, and paper alongside it and those organic materials make up 51.4% of landfilled municipal solid waste. Wasted food on its own is responsible for 58% of landfill methane emissions, and landfills are the third largest source of human-caused methane in the country. Composting diverts that waste and turns it into a rich soil amendment for free.
Composting sounds more complicated than it is. You are basically piling organic material in a bin and letting microorganisms break it down into soil. The process happens with or without your help. Your job is just to create the conditions that make it happen faster and without smell.
This guide covers a basic backyard composting system. If you only have a small apartment, the same principles apply to indoor worm composting or countertop composting units.
A compost bin or a designated spot in your yard. You can buy a tumbling composter (easiest to turn), build a bin from pallets, or just pile materials in a back corner. A pitchfork or garden fork for turning the pile. A long-stemmed compost thermometer if you want a hot pile, which step 7 explains. A small countertop container for collecting kitchen scraps between trips to the bin. No fancy equipment is required. Composting works with nothing more than a heap of organic material on the ground.
Choose a composting method and location
For a backyard, the simplest option is an open bin or tumbler in a shady or partly shaded spot with good drainage. Place it on bare soil (not concrete) so worms and microorganisms can access the pile from below. A tumbling composter sits on a frame and rotates, which makes turning effortless but costs more. A three-sided bin made from pallets or wire mesh is cheap and effective. Size decides whether the pile can ever get hot, because a pile has to be big enough to insulate itself. University of Maryland Extension puts the minimum at 3 feet by 3 feet by 3 feet, which is 27 cubic feet. NC State Extension says much the same, a pile 3 feet high and at least 3 feet across so it becomes self-insulating and holds heat. Anything smaller still composts. It just composts cold, and step 7 explains why that distinction matters. For apartments or small spaces, use vermicomposting (worm composting in a small bin that fits under a sink). A countertop electric unit dries and grinds food rather than composting it, as the last FAQ explains. Position your bin within easy walking distance of your kitchen so you will actually use it. If it is at the far end of the yard, you will stop making trips when it rains.
Learn what goes in and what stays out
Compostable materials fall into two categories: greens (nitrogen-rich) and browns (carbon-rich). Greens include fruit and vegetable scraps, coffee grounds and paper filters, tea bags, fresh grass clippings, and plant trimmings. Browns include dry leaves, straw, dried grass, and untreated wood chips, plus paper and cardboard with conditions attached. EPA's home composting guidance spells those conditions out: shredded paper should be non-glossy and uncolored, cardboard should carry no wax coating, tape, or glue, tea bags should have no staples, and eggshells go in crushed. EPA's avoid list is longer than the usual one. The familiar entries are meat, fish, and bones; cheese and dairy; and fats, oils, and grease. EPA also says to keep out compostable foodservice ware and compostable bags, herbicide-treated plants and grass, aggressive weeds and weeds that have gone to seed, and diseased or pest-infested plants. Its list runs on past that to treated or painted wood, pet waste and cat litter, dryer lint, glossy paper, and produce stickers. The compostable-packaging entry is the counterintuitive one, and the reason is that those products are designed to break down in the sustained heat of a commercial facility. Cooked food is borderline. Small amounts of cooked vegetables are fine. Large amounts of cooked food, especially anything oily or seasoned, can attract rodents.
Heads up: Never add meat, fish, or dairy to a home compost bin. These materials attract rats, raccoons, and flies, and they create intense odors as they decompose. Commercial facilities take them because they hold high temperatures for days under controlled conditions. A backyard pile does get hot, but holding it hot, evenly, all the way to the edges is the part that is hard to do at home. And the pests and the odor arrive whether or not the pile is hot.
Layer greens and browns in the right ratio
The ideal ratio is roughly two to three parts browns to one part greens by volume. That ratio is EPA's own, worded as adding at least two to three times the volume of browns to the volume of greens. It provides the right balance of carbon and nitrogen for the microorganisms that break everything down. Too many greens and the pile becomes slimy and smelly (excess nitrogen produces ammonia). Too many browns and the pile just sits there doing nothing because there is not enough nitrogen to fuel decomposition. Kitchen scraps arrive all year while dry leaves arrive in autumn, so keep a bag of dry leaves, shredded newspaper, or cardboard near your bin. Every time you add kitchen scraps, cover them with two to three times their volume in browns. This also prevents flies and reduces odor.
Keep the pile moist like a wrung-out sponge
Your compost pile needs moisture to support the microorganisms doing the work. The ideal moisture level is like a wrung-out sponge. If you squeeze a handful of compost material, a drop or two of water should come out. More than that is too wet. No moisture at all is too dry. In rainy climates, you may need a lid or tarp to keep the pile from becoming waterlogged. In dry climates, water it every week or two. Kitchen scraps add a lot of moisture on their own, so during wet months you may need extra browns to absorb excess water. During dry summer months, spray the pile with a hose when you turn it.
Turn the pile every one to two weeks
Turning introduces oxygen, which the decomposing organisms need to work efficiently. Without oxygen, the pile goes anaerobic (airless decomposition), which is slow and produces sulfur compounds that smell like rotten eggs. Use a garden fork or pitchfork to move material from the outside of the pile to the center, and from the center to the outside. This ensures everything gets exposed to the hot, active center of the pile where decomposition happens fastest. A tumbling composter makes this easy because you just spin it. For a bin or pile, turning takes about five minutes with a fork. You do not need to be thorough. Even a rough mixing adds enough oxygen.
Troubleshoot common problems
If your pile smells bad, it is either too wet or has too many greens. Add browns (dry leaves, shredded paper) and turn it. If it is not breaking down, it is either too dry or has too many browns. Add water and some fresh greens, then turn. If you see fruit flies, bury food scraps in the center of the pile instead of leaving them on top. If you see large pests (rats, raccoons), make sure you are not adding meat or dairy, and use a bin with a secure lid. A healthy compost pile should smell like earth or have no noticeable smell at all. If it smells like ammonia, add more browns. If it smells like sulfur, it needs more air (turn it more frequently).
Harvest finished compost
Compost is ready when it looks and smells like dark, crumbly soil. You should not be able to identify any of the original materials. The process takes two to six months depending on the size of your inputs, how often you turn, and the temperature. Hot composting (maintaining high temperatures through frequent turning and correct ratios) finishes in six to eight weeks, and the temperature is the point rather than a side effect. EPA puts the working range at 131 to 160 degrees Fahrenheit and says pile temperatures must stay at 131 degrees or above for several days to meet the standards for reducing pathogens. NC State Extension splits that finer, with over 130 degrees killing most pathogens harmful to people and pets and over 140 degrees destroying most weed seeds. A long-stemmed compost thermometer pushed into the middle of the pile is how you find out which side of those numbers you are on. Cold composting (letting it sit with minimal intervention) takes four to twelve months, and the ease comes at a cost worth knowing about. NC State puts it plainly, saying the decay is a lot slower and that seeds and pathogens will not be destroyed. For leaves, coffee grounds, and vegetable trimmings that is perfectly fine. It is also the reason not to put diseased plants, weeds that have gone to seed, or anything you would rather not see again into a pile you never intend to heat. Harvest from the bottom of the pile where material has been decomposing longest. Screen out any large pieces that have not fully broken down and toss them back into the active pile. Use finished compost as a top dressing for garden beds, mix it into potting soil, or spread it on your lawn.
Composting is one of those things that seems complicated until you actually do it. Pile up browns and greens at two to three parts browns to one part food scraps. Keep it moist. Turn it occasionally. In two to six months, you have rich, dark compost that your garden plants love. Start collecting kitchen scraps in a countertop bin tonight. When it fills up, dump it into your compost bin and cover it with dry leaves or shredded paper. That is the entire routine. The finished compost you produce costs nothing, and it is the one soil amendment whose entire history you know, because you put every input into it yourself. It closes the loop from your kitchen to your garden and back to your kitchen.
Questions we get asked about this
Answers from experience, not a textbook.
Not if you do it correctly. Rats are attracted to meat, dairy, cooked food, and exposed food scraps. If you only compost fruits, vegetables, coffee grounds, and yard waste, and you bury fresh scraps under a layer of browns, pests are not a significant issue. A bin with a lid and no gaps larger than a quarter inch provides extra protection. Open piles in areas with known rat problems should be enclosed in quarter-inch hardware cloth, which is exactly what NC State Extension recommends alongside keeping meat and dairy out.
Yes. Decomposition slows down significantly in cold temperatures, but it does not stop entirely. The center of an established pile retains warmth even when the outside freezes. Continue adding materials throughout winter. The pile will not shrink much, but it will resume active decomposition as soon as temperatures rise in spring. Material stockpiled through the winter tends to break down quickly once the pile warms up again. You can also insulate the bin with straw bales or leaves to retain heat.
With active management (correct ratios, regular turning, proper moisture), hot composting produces finished compost in six to eight weeks. With minimal management (piling and occasional turning), cold composting takes four to twelve months. Between those two sits the ordinary case, where turning every week or two produces usable compost in two to four months during warm weather. The speed depends on the size of your inputs (smaller pieces decompose faster), temperature, moisture, and how often you turn.
Yes. Vermicomposting uses red wiggler worms in a small bin that fits under a kitchen sink or in a closet. The worms eat food scraps and produce castings (worm poop) that make excellent fertilizer. A worm bin does not smell if maintained correctly, and you size it by surface area. University of Maryland Extension puts a 2.2 square foot bin at 2 to 3 pounds of kitchen scraps a week. It also wants the worms held between 55 and 75 degrees Fahrenheit, which rules out an unheated garage in a cold winter. Electric countertop units are another option, but they are doing a different job. They dry and grind food with heat instead of letting microorganisms decompose it. What comes out is dehydrated ground food rather than the dark crumbly material step 7 describes, and it still has to finish breaking down in soil or in a compost pile. We could not find an independent authority that has tested what they produce.
Garden Starter
How to Grow Tomatoes
How to Start a Garden
How to Compost
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