Our guide to the good, the bad, and the so-so compost ingredients.
By Willi Evans Galloway
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The Bad Stuff
The following items should never be added to compost, because they could introduce harmful pathogens, toxins, and nonbiodegradable material.
Diseased plants must be disposed of in the garbage or burned. Adding them to compost could spread the disease.
Dog, cat, pig, and reptile manures (and associated bedding) may contain parasites or dangerous pathogens that are harmful to humans, particularly pregnant women, children, and people with compromised immune systems. Never add them to your compost.
Gypsum board scraps could contain paint and other undesirable toxins.
Materials from the side of the road, including grass clippings and leaves, could contain petroleum residues (such as oil), toxins, and nonbiodegradable materials.
Meats, dairy products, bones, and fish decompose slowly, smell, and attract animals.
Paper, especially glossy paper, printed with colored ink, may contain heavy metals. Black-and-white newspaper is safe.
The So-So Stuff
Many things found in the average home are nontoxic and biodegradable and come from a known source—but they aren't great compost ingredients because they break down slowly, mat together, or don't add many nutrients.
Black-and-white newsprint and office paper can be used in the compost pile if you're desperate for brown materials, but they must be shredded. Try using the newspaper in sheet mulching projects and recycling office paper instead.
Cardboard is best used in sheet mulching. Shred or chop it into small pieces if composting.
Dryer lint may contain synthetic fibers that will never decompose. Even natural-fiber lint adds no benefit to compost.
Human and pet hair can be added in small amounts, if you keep in mind that it breaks down slowly, mats easily, and sheds water.
Natural-fiber cloth doesn't add any benefit to the compost pile. Consider using burlap bags under wood chips to prevent weeds instead.
Sawdust must be used in moderation, because it breaks down very slowly and can lock up nitrogen. Never use sawdust from treated or painted wood.
Vacuum bags may contain synthetic carpet fibers and other nonbiodegradable items.
Wood ash adds potassium (potash), but it is an extremely alkaline material and should be used in small amounts.
Wood chips should be used as mulch around ornamentals because they break down so slowly.
Cowpie Caution
Cow manure may contain E. coli O157:H7, a very dangerous pathogen that can cause severe illness and even death. "It's hard to meet time and temperature requirements to kill pathogens in a home compost pile," says soil scientist Craig Cogger, Ph.D. We don't recommend adding it to home compost ever because of the health risk. But if you're tempted to use it, you must wait at least four months after you add it to your soil before you can harvest, to make sure the pathogens are no longer active. Wear gloves when handling manure and wash your hands thoroughly.
