How to Compost at Home

Composting needs a bit of outdoor space, ideally at least a few feet square so the pile is large enough to hold heat and break down efficiently. Choose a flat spot with good drainage, easy to reach year-round. Clear away grass and weeds and loosen the soil to about eight inches. Set the bin directly on the soil so earthworms and microorganisms can move into the pile. A closed or enclosed bin helps control odor and keeps a patio or lawn looking tidy, and lining it with chicken wire keeps out dogs and wildlife.

Green materials are the wet, nitrogen-rich ingredients that feed the microbes doing the work. Grass clippings are very high in nitrogen and work well layered into a pile. Manure from horses, cows, chickens, rabbits, and goats adds nitrogen along with other nutrients, and bat guano is especially nutrient-dense, prized by some gardeners as a top fertilizer. Other greens include fruit and vegetable scraps, coffee grounds and paper filters, plant cuttings, flower tops, and seaweed.

Brown materials are dry and high in carbon, the energy source for compost microbes. They include fallen leaves, shredded branches, hay, straw, used tea and paper tea bags (without staples), and wood shavings or sawdust from untreated wood. Shred paper, newspaper, and tissues, and break cardboard into small pieces before adding them. Skip glossy or heavily dyed paper, which carries too many additives and inks. Crushed eggshells add calcium to the mix. Straw is a good choice for working into clay soil because it breaks down slowly, and its particles help keep heavy soil aerated.

Some tree leaves are especially nutrient-rich, including ash, poplar, maple, and willow. Whole leaves compost fine, but shredding them speeds things up. Avoid walnut leaves, which release a compound (juglone) that can stunt many plants. Oak leaves are slow to break down and slightly acidic because of their tannins, so some gardeners compost them separately for use around acid-loving plants like blueberries, strawberries, and azaleas, though finished compost tends to settle near neutral either way.

Keep dog, cat, pig, and human waste out of the pile, since it can carry parasites or bacteria that make people sick. Inorganic materials like plastic, metal, glass, ceramic, used cat litter, particleboard, and plywood won't compost at all. Avoid meat, bones, poultry, fish, whole eggs, fats, grease, and oils, which cause foul odors, feed harmful bacteria, and draw animals and insects. Steer clear of sawdust or chips from pressure-treated or chemically preserved wood, too. It often has a greenish tint from copper, and older treated lumber, made before the mid-2000s, can contain arsenic.

Start the pile with a four-inch base of twigs, hay, or straw to let air circulate underneath. Add a four-inch layer of brown materials, then a thin coat of garden soil, which seeds the pile with the bacteria that kick off decomposition. Next add a four-inch layer of green materials and sprinkle on an activator to feed the bacteria extra nitrogen and protein. Good activators include alfalfa meal, fresh manure, high-protein dry dog food, or bone, blood, or cottonseed meal. Keep building in the same pattern until the bin is full, aiming for more brown material than green overall, roughly two to three parts browns to one part greens, which keeps the pile from turning wet and smelly.

A healthy pile heats up fast, reaching about 140 degrees Fahrenheit within the first week to ten days, and a well-managed pile can climb to 130 to 160 degrees. Those high temperatures help kill weed seeds and reduce pathogens. Eventually the most active bacteria start to die back as the heat peaks and the oxygen in the pile runs low. The pile then begins to cool, which is the signal that it's time to turn it. A compost thermometer takes the guesswork out of tracking the temperature.

Turn the pile with a shovel, rake, or a dedicated aeration tool. Move the drier outer edges into the center and break up any clumps, adding a little water if the material seems too dry. Turning every couple of weeks, or whenever the temperature drops to around 110 to 120 degrees Fahrenheit, keeps things moving; compost matures faster with regular aeration and moisture checks. Tumbling composters, sold by many manufacturers, handle the aeration for you.

An active compost pile does best at about 50 to 60 percent moisture. To measure it precisely, weigh a sample, dry it out completely, and weigh it again. Subtract the dry weight from the wet weight, divide that difference by the original wet weight, and multiply by 100 to get the moisture percentage.

The simpler method is the squeeze test. Grab a handful: if water drips out, it's too wet; if it crumbles apart, it's too dry. If it holds its shape without releasing water, like a wrung-out sponge, the moisture is right where you want it.

Compost is ready when it stops giving off heat and looks dark brown, loose, and crumbly. For a quick maturity check, seal a handful in a plastic bag for a day, then open it: finished compost smells like fresh earth, while a foul or ammonia-like odor means it needs more time. Many gardeners also brew compost tea with finished compost, steeping a chunk in a bucket of water for about five days, then straining it through cheesecloth. The resulting liquid is rich in nutrients and works as a natural fertilizer.