What Not to Add to Your Home Compost Pile

A good rule of thumb to follow if you’re unsure whether you should put something in your compost pile – when in doubt, leave it out! Creating perfect compost is both a science and an art that requires attention to detail and patience. By being selective about what goes into your backyard composting bin, you avoid the pitfalls of adding non-beneficial, potentially harmful items and contribute to the creation of a nutrient-rich resource for your garden.

For more information and resources on how to compost effectively, check out your local extension office or community composting programs. These resources can provide valuable guidelines tailored to your local environment and conditions, helping you succeed in your composting endeavors.

These food items can attract rats, flies and other pests and are likely to produce unpleasant odors as they decompose. They can also create an environment that promotes harmful bacteria, which can be hazardous if you use your compost on food crops.

Furthermore, the Environmental Protection Agency states that small backyard composting piles usually won’t get hot enough to break down these food products. However, empty eggshells are okay if you crush them first.

Wood that’s been treated or pressure treated and the sawdust from these woods contain harmful chemicals like creosote or arsenic. These chemicals can be toxic to plants, damaging your soil and beneficial microbes’ health. Furthermore, even if these chemicals weren’t harmful, they’re intended to repel moisture, the key ingredient to biodegradation.

Also, avoid composting wood that’s been painted. Particle board, plywood and medium-density fiberboard should also be left out of your composting pile because they often contain synthetic binding agents and chemicals that might not break down. These materials could also harm beneficial organisms in your compost.

Dogs are omnivorous, and cats are carnivorous, meaning their intestines can include a host of resilient parasites and pathogens. Their feces can also contain parasites, pathogens, bacteria and viruses that could harm humans, posing health risks if you use the compost in your food garden. Cat feces can be especially dangerous.

On the flip side, manure from animals that solely eat plants can be very beneficial in your compost. The exception is if the manure comes from a sick animal, which could pass harmful bacteria or viruses through its waste.

The inks and chemicals used in colored and glossy paper may contain heavy metals that could contaminate your compost and eventually leach into the soil. These metals could be toxic and potentially harmful to plant life.

The coating on glossy paper, like those used in magazines, is often made from plastic, which isn’t compostable. However, newsprint and other non-colored, non-glossy paper are safe to use in your pile.

Plants with disease or pest problems or containing pesticides can transfer these problems back into your garden. Adding diseased or insect-infested plants can spread pathogens that survive the composting process and infect your garden when you use the compost.

Fat, grease, oil and lard can throw your compost’s moisture content out of balance. Moisture is critical to biodegradation. They can also reduce air circulation, the second key ingredient of a healthy compost pile. Cooking oils may also attract pests. These oils don’t just include liquids but also any items with oils on them, such as paper towels saturated with cooking oil or cardboard pizza boxes soaked with grease from the pizza.

The fruits, shells, leaves and branches of walnut trees can be toxic to some plants when used in your compost because they contain juglone. This chemical has been known to damage potatoes, tomatoes, lilies and hydrangeas.

Ashes produced from coal or charcoal can contain heavy metals that could be toxic to plants and leach into water supplies. They can also alter the pH in your compost, potentially rendering the soil less suitable for plant growth. Wood ash is safe to mix in your compost pile, but coal ashes and charcoal from grills aren’t safe.

The residual chemicals on plants used to kill insects or control diseases can kill beneficial organizations, helping break down waste in your compost. They could also enter the food chain if you use compost that includes synthetic pesticides and fertilizers in your vegetable garden.

These inorganic materials won’t break down and will contaminate your compost, making it unsuitable for use in your garden. These items also pose a potential hazard to wildlife and people working in the garden.

While you may not be able to see it, most textiles are either entirely made from synthetic fibers or a combination of synthetic and organic fibers. Synthetic fibers commonly derived from petroleum include nylon, rayon, polyester and elastane. Drying clothes can potentially introduce these fibers to the lint.

When you dry clothing or other items made from synthetic materials, those fibers end up in your dryer lint. Likewise, the fibers from carpets constantly shed, meaning you pick up these synthetic fibers and tiny pieces of plastic when you vacuum. Thus, neither dryer lint nor vacuum dust should be added because they’re non-biodegradable and introduce microplastics into your composting.

Straight tobacco is compostable, but cigarettes contain much more than tobacco. Cigarettes contain certain chemicals shown to inhibit plant growth. The tiny plastic particles in cigarette filters make it so they won’t break down.

You switched to biodegradable and compostable plastics to be green and do your part to help support the planet by reducing carbon emissions. Compostable plastic is biodegradable, but not every biodegradable plastic is compostable. Also, a small at-home compost pile typically can’t break down compostable plastic.

These items must be sent to a commercial composting facility with higher temperatures and different breakdown conditions. Some community-wide residential compost collection programs accept compostable plastic, but be sure to ask before recycling your plastics with your local program.

Because grass clippings have a high nitrogen and moisture content, they can cause your small compost pile at home to heat up well above the ideal temperature range. Compost that’s too hot can lead to unwanted odors. Furthermore, lawns treated with fertilizers and pesticides can harm your pile and the vegetation you apply it to.

Any personal hygiene item containing human feces, blood or other fluids, such as tampons or diapers, shouldn’t be included in your compost bin. Items contaminated with solids or fluids produced by the human body pose a significant health risk.

Orange peelings, lemon peels, lime peels, and other citrus fruits can fluctuate the pH of your compost bin, slowing down the decomposition process. Also, if you’re using worms as part of the composting process, citrus can kill these beneficial organisms.

Cooked grains and freshly baked bread, especially those with glazes or a lot of sugar, can breed harmful bacteria. Cooked rice is especially noted for bad bacteria growth in a compost pile. Confections can also attract pests, including flies and rodents.

You can compost uncooked rice and pasta and plain bread that’s so stale that it’s hard. However, you should keep these in moderation and always bury them as deeply as possible in your compost pile.

Similar to coatings on glossy pages, coated packaging can also introduce undesirable components to your composting pile. Food packaging made of plastic, foil or other non-sustainable material shouldn’t be placed in your compost. Examples include waxy-lined coffee cups, juice boxes, milk cartons and foil-lined cookie or cracker bags.

• Cardboard egg cartons
• Chopped or chipped branches and twigs
• Coffee grounds
• Crushed eggshells
• Disease/pest-free houseplants
• Dry hay, leaves and straw
• Grains and hops
• Healthy herbivore manure
• Natural cork
• Non-invasive weeds without mature seeds
• Non-woody pruning
• Nutshells (minus walnuts)
• Paper coffee filters
• Paper towels and toilet paper rolls
• Pet bedding from healthy rabbits, hamsters, gerbils and guinea pigs
• Sawdust from untreated wood
• Shredded brown paper bags
• Shredded newspaper
• Shredded, uncoated and sticker/tape-free paper and cardboard
• Shrub pruning
• Spent flowers
• Sticker-free fruits and vegetables
• Tea grounds and leaves
• Untreated wood ash (in moderation)

Further information about composting, how to compost and its benefits:

• United States Department of Agriculture
• Environmental Protection Agency
• Institute for Local Self-Reliance
• Cornell Waste Management Institute
• USDA National List of Allowed and Prohibited Substances for Organic Gardening