Almost all organic material found around the average home is appropriate for backyard composting. Here are a few exceptions.
Coal or charcoal ashes. Although wood ashes from a wood-burning stove or fireplace can be valuable compost materials for acidic soils, coal ashes and ashes from a charcoal barbecue contain sulfur oxides and other compounds toxic to the soil. Keep these toxic ashes out of the compost pile.
Diseased garden plants. Discard any plants that have died or you pulled up because they're diseased. The bacterium, virus or fungus that caused the disease may survive the composting process and infect the area where you apply the finished compost.
Glossy paper with colored ink. Newsprint, even with color pictures, is an appropriate material for home composting; on the other hand, glossy magazines with color photography are not. The printing industry has made some progress in developing water- or soy-based inks for high-gloss color printing, but most glossy magazines still contain inks that could contribute toxins to the compost pile.
Invasive weeds. Most weeds are fine additions to the compost heap, but a few exceptions are best disposed of in the trash. Particularly invasive weeds — such as buttercup, morning glory and quack grass — can survive the low temperatures of a passive pile and live on to infest the composted area. Some weed seeds, such as those of bur clover and cheeseweed, have been known to survive the temperatures of even hot compost piles. The wise course of action is to keep compost free of these tenacious species.
Meat and meat products. Exclude meat, meat products, grease and bones from the compost pile unless it's hot and carefully managed.
Pesticide-treated plant material. Exclude grass clippings, weeds and other plants recently treated with pesticides, unless the plants were soaked by a steady rain after the pesticide application. Although most pesticides break down in the composting process and become harmless, that's not always the case. Assume that the residual effect of the pesticide last as long in the compost pile as it would on the targeted plant.
Pet litter. Don't place cat or dog waste in the compost pile. Cat waste can contain parasites that cause brain and eye diseases in children and unborn infants. A cat, especially an outdoor one, can appear healthy but still carry these microorganisms.
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