Composting is a practice in which one speeds the natural breakdown of organic matter to make a nutritional soil amendment for gardens and yards. It really doesn't take that much time and it can be very cheap to make, but many people hesitate to set up their own compost piles because they don't know what sorts of materials to compost and in what proportions. Normally you should keep a ratio of three parts "brown" components for every one part of "green" components.
"Green" ingredients typically have a high nitrogen content, but need not be green in color. Green compost includes chicken, horse, and cattle manure. Kitchen scraps such as potato peelings, orange rinds, apple cores, or any other bits of fruits or vegetables work as well. Fresh cut lawn clippings, fleshy yard weeds, flower heads, and even algae and fresh-water aquarium scum all have high doses of nitrogen. A good rule of thumb is to check to see if the plant is fleshy and moist. If so, it's usually safe to use as "green" composting material.
"Brown" compost ingredients are those ingredients that have high carbon content. Along with a smaller ratio of green ingredients, brown compost works with air and water to speed the decay process. A general rule of thumb with brown compost is that any plant, tree, or flower with a woody texture and bark-like exterior is a safe choice. These include: dry vegetable vines, vegetable stalks, twigs, hedge trimmings, fallen leaves, dried lawn trimmings, straw, and tree bark. As with all brown compost ingredients, they should be dried thoroughly and free of mold, bacteria, or parasitic infection.
There will always be a few things that may cause you to stop and scratch your head, wondering whether or not they're safe for compost. Here are some things to avoid putting in the compost heap.
Reptile, cat, dog, pig, and human fecal matter are not safe for composting as they often contain large amounts of dangerous bacteria which could infect the compost and make it a health hazard to anyone nearby. For the same reason, one should never use dying or diseased plant matter.
Gypsum board, plywood, paper, and other treated wood products contain chemical agents that could be toxic and impede the decay process.
Animal and dairy products, including bones, will cause unpleasant odors as they rot, and may attract animal pests or foster disease.
Finally, clippings or plants taken from the roadside should never be used in compost, as they may have petroleum and oil residue which would be harmful to anything the compost was placed on.