Composting is a natural biological process where organic materials are broken down by microorganisms into humus, a dark, stable, and nutrient-rich soil amendment. This process transforms yard waste and kitchen scraps into a valuable resource, diverting waste from landfills while enriching garden soil. Successful composting relies on managing four main ingredients: carbon-rich material, nitrogen-rich material, water, and air. This guide offers a practical, step-by-step approach to starting and maintaining your own compost pile.
Site Selection and Material Preparation
Choosing the right location for your compost system focuses on convenience and environmental factors. A spot with good drainage and access to a water source is beneficial for maintaining the correct moisture level in the pile. Partial shade is recommended, as it prevents the pile from drying out too quickly in direct sunlight, which can slow decomposition.
Compost containers can range from a simple, freestanding pile to manufactured plastic tumblers, wire cages, or wooden bins. Wire cages and wooden bins allow for greater airflow, while tumblers make turning the material much easier. Place the structure directly on the soil to allow beneficial organisms like worms and microbes to colonize the pile and for excess water to drain away.
The ingredients for your compost are categorized into “Browns” (carbon-rich) and “Greens” (nitrogen-rich). Carbon-rich Browns include dried leaves, shredded paper, cardboard, straw, and wood chips. Nitrogen-rich Greens consist of fresh materials like fruit and vegetable scraps, coffee grounds, tea bags, and grass clippings. Shredding or chopping materials into smaller pieces is recommended because it increases the surface area available to the microorganisms, significantly speeding up the decomposition rate.
Certain items should never be added to a home compost pile to avoid attracting pests or introducing pathogens. Prohibited materials include meat scraps, bones, dairy products, oils, fats, and grease. Also, avoid composting pet waste from carnivorous animals, diseased plants, or yard waste treated with chemical pesticides or herbicides.
Constructing the Composting Layers
The initial construction involves creating a layered structure to ensure proper aeration and a balanced mix of materials. Begin by laying a four to six-inch thick base layer of coarse, bulky Browns, such as small twigs or wood chips. This foundational layer promotes drainage and allows air to circulate up into the center of the pile.
Next, alternate layers of Brown and Green materials to achieve the ideal carbon-to-nitrogen (C:N) ratio for microbial activity. While the ideal C:N ratio is approximately 25:1 to 30:1, a practical rule for home composting is to use roughly two to three parts Browns to one part Greens by volume. This ratio ensures the microorganisms have enough carbon for energy and enough nitrogen for reproduction.
A typical layering sequence involves a 6-inch layer of Browns, followed by a 2 to 3-inch layer of Greens, and then a thin layer of finished compost or garden soil. The soil or finished compost acts as an inoculant, introducing the necessary bacteria and fungi to kickstart decomposition. Repeat this alternating process until the pile reaches a size of at least three feet high and wide, which is necessary to generate and retain heat.
After adding each layer, especially the dry Brown material, moisten it lightly with water. The entire pile should be uniformly damp, aiming for the consistency of a wrung-out sponge, which is the perfect moisture level for aerobic microbes. Too little moisture halts decomposition, while too much saturates the material, leading to anaerobic conditions and foul odors.
Active Management and Curing
Once the pile is built, active management is required to sustain the microbial activity that drives decomposition. Aeration, usually achieved by physically turning the pile, is required because aerobic microbes rapidly consume the oxygen within the pile. Turning the compost introduces fresh oxygen, preventing the pile from becoming dense and anaerobic, which causes unpleasant odors.
For the fastest results, known as “hot composting,” the pile should be turned every few days when the internal temperature begins to drop. The ideal temperature range for rapid decomposition and killing weed seeds and pathogens is between 131°F and 160°F. Monitoring this temperature with a long-stemmed compost thermometer helps determine when turning is necessary to keep the microbes active.
A strong ammonia or rotten egg smell indicates an imbalance, typically too much nitrogen (Greens) and insufficient oxygen. This problem is solved by immediately turning the pile to introduce air and mixing in dry Browns, like shredded leaves or paper, to absorb excess moisture and rebalance the C:N ratio. Conversely, if the pile is cold and decomposition has stalled, it is often too dry or has too many Browns, requiring the addition of water and more Greens to reactivate the microbes.
The process is complete when the compost has transformed into a dark, rich, uniform material that no longer resembles the original scraps. Finished compost will be crumbly in texture and possess a pleasant, earthy aroma, similar to forest soil. The pile will no longer heat up after turning, indicating the active phase of decomposition is over. Allow the finished compost to “cure” for several weeks without turning to stabilize the final product.