Avoid common composting mistakes by knowing exactly what to add—and what to skip.
Think you can toss anything in your compost bin? Think again! The secret to great compost isn’t just piling up scraps—it’s knowing exactly what to include and what to avoid. Composting is nature’s recycling system, turning waste into nutrient-rich soil—but only if you get the mix right. This guide will help you dodge common mistakes and explain what you can compost to make your compost bin a success.
What is Composting?
Composting encourages Nature to speed up its natural recycling process in a more controlled way. By piling up compostable materials (see below), microbial decomposers break them down into plant-usable nutrients and humus—the fluffy, dark substance that enriches soil.
A healthy compost pile usually needs to be at least 3 feet wide and tall to heat up and speed decomposition. When managed well, composting reduces waste, saves money compared to buying compost, and completes the nutrient cycle in your garden. Read our complete guide on how to compost and how to make a DIY compost bin.
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What Can You Compost?
In general, we only compost things that were once alive but are now not. In soil science terms, we refer to that as organic material. It’s not the same as the food label meaning of organic. Inorganic materials are things like a rock, old carpet, or the transmission from your car. Your ‘83 Ford pickup out behind the shed turning into a pile of iron oxide doesn’t count as composting.
When deciding what is okay to compost, it should not only be an organic material but also typically plant-based. Animal fats, meat, dairy, and leftover pasta salad are not suitable for normal composting, although they can be composted using bokashi methods. If it once had leaves, that’s a good starting point.
Related: How to Make Compost Tea
Here’s a handy list of common compostable items, along with notes and trusted sources:
| Compostable Item | Source | Notes |
|---|---|---|
| Raw Fruits and Vegetables (including peels) | University of Illinois Extension | Avoid moldy produce with oils or salt; citrus in moderation. |
| Coffee Grounds and Filters | Cornell Waste Management Institute | High in nitrogen; filters must be unbleached and free of plastic. |
| Eggshells | Washington State University Extension | Best crushed for faster breakdown and calcium boost. |
| Grass Clippings and Yard Trimmings | University of California ANR | Yes, only if herbicide-free and not too thick (can mat down). |
| Houseplants (dead and trimmed) | University of Illinois Extension | Ensure they’re not diseased or chemically treated. |
| Leftover Grains (e.g., from brewing) | Cornell Waste Management Institute | Great nitrogen source; don’t overload or it may smell. |
| Manure (chicken, cow, sheep, pig) | Washington State University Extension | Yes, from healthy animals only. Aged/composted manure is best to reduce pathogens. |
| Newspapers (non-glossy) | University of Illinois Extension | Most modern papers use soy inks. No glossy inserts or colored fliers. |
| Nutshells | Cornell Waste Management Institute | Harder shells (e.g., walnut) break down slowly. Avoid salted or flavored nuts. |
| Paper Napkins (plain, unbleached) | University of Illinois Extension | Only if plain, unbleached, and free of chemicals or food grease. |
| Raked Leaves | University of California ANR | Shred or mix with greens to balance carbon. |
| Rice and Other Grains | Cornell Waste Management Institute | Yes, but in small amounts. Can attract pests or smell if too much is added at once. |
| Shredded (non-glossy) Paper and Cardboard | University of Illinois Extension | Great for carbon. Avoid tape, staples, and plastic coatings. |
| Spent Potting Soil (roots included) | Washington State University Extension | Enriches your pile with leftover organics. |
| Tea Bags (plastic-free) | Cornell Waste Management Institute | Yes, but many brands use plastic-based bags. Only compost if confirmed plastic-free or remove bag and compost the leaves. |
| Weeds (non-seeding, no rhizomes) | Washington State University Extension | Avoid invasive weeds or those that have seeded. |
| Wood Chips and Bark (in moderation) | University of California ANR | Yes, in moderation. High in carbon and slow to break down; better in bottom layers or as mulch. |
Tip: Chop or shred materials to speed decomposition. Large sticks or branches can take years. If it’s larger than your finger, you may wish to pile it separately or chip it first. A sequoia will eventually become compost on the forest floor, but it will take a couple of centuries.
What Can’t You Compost?
If it once walked around, swam, or slithered, it shouldn’t be put in the compost. The reason we don’t compost meats, dairy, and cooked food is partly because these items can smell quite bad as they break down and partly because the odor they give off attracts pests.
Just like the fragrant goodies in your trash can, food scraps will also inspire skunks, rats, and raccoons to get into mischief in your compost pile. Most of us don’t want more raccoons visiting us at night. Bears have a keen sense for locating human food, which they adore, and can be a large, furry, scary problem, even if you live in town. Once these pests have rooted through your compost pile, they may turn their attention to other matters, such as your grill, the screens on your windows, the bird feeder, or simply hang out on your back deck waiting to say hello. Surprise!
I like to consider nature as a guide when selecting what to compost. If, in nature, the food turns back into soil by simply decomposing after it dies, like dead leaves and grasses, flowers, and herbaceous plants, then it is perfect for composting. If, in nature, it attracts vultures and crows, like a roadkill deer, and usually gets eaten and digested by a scavenger before it would turn to soil, then it’s not for my compost pile.
Depending on your preferences, you may wish to omit eggshells, nut husks, and cardboard from the compost pile, as they can take a long time to break down. If you don’t care about a few recognizable eggshells in your finished compost, by all means, toss them in.
| Non-Compostable Item | Source | Why/More Info |
|---|---|---|
| Chicken, beef, pork, fish (incl. shellfish) | Clemson Cooperative Extension | Rot, smell, and attract pests like rats and raccoons. Includes bones, skin, and fat. |
| Cooked meal scraps | University of Georgia Extension | Contain oils and spices that attract pests and slow composting. |
| Dairy (milk, cheese, butter, yogurt) | University of Wisconsin Extension | Causes odor and pests; even small amounts can sour the pile. |
| Fats, oils, grease | University of Missouri Extension | Slow to break down and can coat materials. Includes dressings, sauces, and fried foods. |
| Pet waste (cats and dogs) | UC Agriculture & Natural Resources | Contains harmful pathogens and parasites. Home compost can’t reach high enough temps. |
| Diseased plant material | NC State Extension | Home piles often don’t get hot enough to kill pathogens. Avoid blight, mildew, rust. |
| Bread, donuts, cookies, cakes | University of Maryland Extension | Mold easily and attract pests. Includes cookies, crackers, pizza crusts. |
| Weeds with developed seeds | Colorado State University Extension | Seeds may survive and spread in your garden. |
| Invasive plant species | University of Minnesota Extension | Can regrow from roots or rhizomes. Avoid bindweed, quackgrass, and others. |
| Pressure-treated lumber scraps | University of Florida Extension | Treated wood contains toxic chemicals like arsenic and copper. |
| Used toilet paper | University of Nevada Extension | Often bleached or perfumed; not recommended due to hygiene concerns. |
| Cat litter | Cornell Waste Management Institute | Contains pathogens and should not be used. Even biodegradable types are unsafe for home piles. |
| Plastics (even compostable types) | Washington State University Extension | Require high heat to break down; home systems don’t get hot enough. |
| Glossy or coated paper | University of Vermont Extension | Contains plastics or toxic inks. Safe alternatives: newspaper, plain cardboard, napkins. |
| Produce stickers | University of Maine Extension | Made of plastic; contaminates compost. Always remove from fruit and veg first. |
Some composting guides may claim a few of the above are okay to compost within certain guidelines and practices, but for the average backyard compost bin, they are better left out of the pile.
FAQs
What about citrus?
I didn’t include citrus on either list because opinions vary. Citrus peels are acidic, and some folks worry that they’ll throw off the pH balance or harm composting worms. That’s a valid concern if you’re using vermicomposting (a worm bin), where acidity can be an issue.
But if you’re composting in a regular outdoor pile or bin, citrus peels are usually fine in moderation. I add mine without problems. They do take longer to break down than some materials—but unless you’re tossing in heaps of oranges and grapefruits, they won’t hurt the pile.
Bottom line: Compost citrus peels sparingly, avoid overloading the pile, and skip them if you’re using worms.
Why can’t you compost pet waste?
It’s a fair question—after all, we compost manure from cows, sheep, chickens, and even pigs. Aged manure from these animals is garden gold! And yes, droppings from small herbivorous pets like rabbits, guinea pigs, and hamsters are fine to compost, along with their paper or wood shavings.
But waste from dogs and cats is a different story. It can contain harmful pathogens like E. coli, Salmonella, and parasites such as Toxoplasma gondii. Most backyard compost piles don’t reach high enough temperatures to reliably kill these organisms, which can pose risks to human health—especially if the compost is used around vegetables or other edibles.
As a general rule, manure from herbivores is compostable; feces from carnivores (and humans) is not.
Can I compost hay and straw?
Yes, you can—but I don’t. Straw is generally seed-free and makes a decent brown (carbon-rich) material. Just keep in mind it may carry herbicide residues, especially if it came from treated grain crops.
Hay is trickier. It’s often baled with weed seeds. Unless your compost pile gets hot enough (130–160°F), those seeds can survive and sprout wherever you spread your compost. I once got a compost load full of weed seeds—thanks to some cow manure—and let’s just say the garden regret was real.
How to keep rats and animals away?
Avoid meat, dairy, and cooked scraps that attract pests. Bury food scraps beneath dry materials and keep the pile warm and aerated to reduce odors and pest visits.
What about flies?
A few fruit flies are normal, but swarms mean too much fresh food or poor airflow. Cover scraps with dry leaves or shredded paper and maintain a balanced mix of greens and browns.
Will it smell bad? How do you reduce odors?
Proper compost smells earthy. Sour or ammonia odors indicate too much moisture or nitrogen-rich materials. Add dry carbon sources and turn the pile regularly for fresh air.
Andy Wilcox
how long does it take to form dirt?
“How long does compost take?” is a great question. The answer: It ranges from a few weeks to 2 years. Why? It depends on how actively you manage it or how quickly you need it. If you turn your pile frequently (every week or so) and manage it to maintain the correct green-to-brown ratios, it will take a month or two. If you just leave it and don’t turn it, letting nature do its thing, then it will take 6 months to 2 years to fully compost. It’s really up to you.
