Why: The purpose is to convert organic materials into compost for garden beds and potting soil. Composting recycles kitchen and yard waste, diverting up to 30% from the trash and consequently reducing landfill waste. Compost adds nutrients and introduces beneficial organisms to the soil, and helps promote plant growth.
Where: The first thing to do when starting a compost heap is to select a good location for it. You want to choose an area that's fairly level with good drainage (so the pile doesn't sit in standing water when it rains). Avoid windy areas, and try to find a location with half-day sun. If the heap gets too much direct sunlight, it will dry out, but if it's in heavy shade, it might not receive enough rain water, or it might remain over-moist. For your convenience, try to keep it close to a water source and at a convenient distance from the house, so you don't have to walk too far every time you want to add kitchen scraps. Finally, keep it away from dog areas, since pet waste can contaminate the heap, and don't place it in contact with wooden buildings, since the process of decomposition will attack the walls just as readily as the materials in the pile.
What: A good compost heap strikes a balance between nitrogen-rich green matter and and carbon-rich brown matter, all kept barely moist (a squeeze test should yield a few droplets of water, but no more). If a compost pile has too much wet, green vegetable matter, it can get rather smelly, and if it has too much dry, brown matter, it takes longer to decompose. Some composters recommend an even ratio of brown to green matter, while others recommend keeping the balance at 1/3 green matter, 2/3 brown. You can tweak the balance as you see fit, and sometimes it will vary depending on season.
What to compost:
• coffee grounds
• used tea
• leaves and stalks
• vegetable/ fruit trimmings
• grass clippings
• straw or hay
• shredded paper
• manure (from herbivores)
• hair and fur
• wood chips
• dryer lint
• nut shells
• fireplace ashes
What NOT to compost:
• meat, fish, and their scraps and bones
• oily or greasy food and paper
• dairy products
• pet waste
• plants treated with herbicides
• coal or charcoal ash
• black walnut leaves or twigs
Materials will break down at a faster rate if the pieces are relatively uniform, so break any larger pieces of wood, etc., into smaller bits before adding them to the pile. Smaller particles also improve the pile's insulation, which will keep the core temperature warm enough to encourage maximum decomposition. The core of the pile can reach 140ºF because of microbial activity, and optimal decomposition occurs between 110º and 160º.
How: Once you've selected your location, start with a layer of straw or twigs, and then alternate moist and dry layers. Add a nitrogen source (like manure or clover) to activate the pile and to speed its decomposition process. When getting started, keep the layers relatively thin and uniform. Once the pile is active, you can add materials by burying them in the center or just incorporating them more fully when you turn the pile, but to get started, try to disperse the elements fairly evenly, as in the diagram below.
Covering the heap with pieces of wood, plastic tarp, or old carpet scraps will help it retain its moisture and heat, and it can also protect it from elements that might upset its balance (like too much rain).
To maintain care of your pile, water occasionally, or let the rain take care of it if you live in a place with sufficient rainfall. Again, you want to keep the pile barely moist, not soaked. Every week or two, give the pile a turn with a pitchfork or shovel to aerate it. If you aren't adding new material very frequently, you can turn it once every four or five weeks.
When: The time that your compost will be ready depends on the particularities of the heap, but generally, it's ready when the material at the bottom of the heap is dark and rich. With a pile started in the spring, it's probably safe to say that some compost would be ready by the fall.
For more in-depth directions, scientific information, and troubleshooting guidelines, here are a couple of helpful links: