Building a compost pile creates more anxiety and obsession among gardeners than any other gardening activity. So before you start a pile, remember one thing: Relax. “There’s no right or wrong way of composting, and people get panicked that they have the wrong recipe,” says Dr. Maynard. “Composting is a natural phenomenon—it’s decomposing; you’re just helping it along a bit.” That said, there are good, bad, and so-so compost ingredients. So before you add an ingredient to your pile, make sure it’s up to the compost quality-control test. Ask yourself four basic questions about each ingredient:
1. Is it biodegradable?
2. Will it help make high-quality, nutrient-rich compost?
3. Did it come from a chemical-free lawn?
4. Is it free of disease, toxins, and other contaminants?
If you answer “no” or “I don’t know” to any of these questions, forgo adding the ingredient to your pile. It’s that easy. Mix and match the green and brown ingredients listed below until you find a compost recipe that works for you. Just keep in mind the carbon-to-nitrogen (C/N) ratio as you build your pile.
Aquarium water, algae, and plants (from freshwater fish tanks only) add moisture and a kick of nitrogen.
Chicken manure has high amounts of nitrogen, phosphorus, and potassium.
Dead houseplants add a dose of nitrogen, but don’t include thorny or diseased plants.
Fresh grass clippings should be mixed with plenty of drier, brown material, or you’ll risk creating a smelly pile.
Green garden debris, such as spent pansies, bolted lettuce, and deadheaded flowers, can all be recycled in the compost bin.
Horse manure contains more nitrogen than cow manure.
Manure from pet rabbits and rodents(e.g., gerbils and hamsters) can be composted with the accompanying wood or paper bedding.
Vegetative kitchen scraps (carrot peelings and the like) should be buried in the pile so they don’t attract animals. Eggshells are okay, too.
Weeds can be composted! No joke. Just remember never to add weeds that have set seed or weeds that root easily from stems or rhizomes, such as field bindweed and Canada thistle.
Brown garden debris, such as corn and sunflower stalks, dried legume plants, and dried potato and tomato vines, adds bulk to the pile.
Hedge prunings and twigs help keep a pile fluffy but should be chipped first so they decompose faster.
Leaves are an abundant carbon source and full of nutrients. Stockpile them in fall so that you have them on hand in summer.
Pine needles decompose slowly. Add only small amounts to your pile. Use excess needles as a mulch.
Straw bulks up a pile, but it should not be confused with hay, which often contains weed and grass seeds and shouldn’t be added to compost (unless you want to deal with the potential consequences).
The No-No List
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 List
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.
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.