What NOT to Compost: The Complete List and What to Do With Each Item Instead
By Ku · Updated March 2026 · 9 min read
Most composting guides spend all their time telling you what to add. Coffee grounds, eggshells, banana peels — the list of what works is long and well-covered. The list of what doesn't work gets less attention, which is a problem, because the mistakes people make adding the wrong things cause real damage: pest infestations, disease spreading into garden beds, piles that smell bad for weeks, and finished compost that's actually harmful to plants.
I've made a few of these mistakes myself. The meat scraps one was educational. The diseased tomato plant one was expensive.
This post covers the things that genuinely don't belong in a home compost pile — not because of some vague concern, but because of specific, documented problems. For each one, I'll explain exactly what goes wrong and what to do with the material instead.
One clarification upfront: "What not to compost at home" is different from "what can't be composted at all." Industrial composting facilities reach higher temperatures, maintain tighter controls, and can process many materials that home piles can't handle safely — including meat, dairy, compostable plastics, and some diseased plant material. This guide covers home composting only.
Category 1: Meat, Fish, Bones, and Dairy
This is the most commonly cited rule, and for good reason. Iowa State University Extension is direct: do not add meat scraps, bones, grease, whole eggs, or dairy products to the compost pile because they decompose slowly, cause odors, and can attract rodents.
The problem isn't that these materials won't break down. They will, eventually. The problems are:
- Odor: Decomposing meat and dairy produce ammonia and hydrogen sulfide — the gases responsible for the worst composting smells. These can persist for weeks and make the pile genuinely unpleasant to manage.
- Pests: The smell of decomposing meat attracts rats, mice, raccoons, foxes, and depending on where you live, larger animals. A single addition of meat scraps can turn a well-managed pile into a pest problem that takes months to resolve.
- Pathogens: Raw meat carries bacteria like Salmonella and E. coli that can survive in a home pile that doesn't consistently reach 130°F+ throughout. If that finished compost ends up on edible crops, the risk is real.
What to do instead
If you want to compost meat, dairy, and cooked food, bokashi is the right method. A sealed bokashi bucket ferments these materials anaerobically at room temperature, with no odor and no pest attraction. The fermented material then gets buried in soil or added to a hot compost pile to finish breaking down. It handles everything a regular pile can't.
Category 2: Diseased Plants
This one causes more long-term damage than almost anything else on this list, and it's easy to get wrong because diseased plants look like perfectly reasonable compost material.
Iowa State University Extension is clear: do not add diseased plant material to the compost pile. Disease organisms will not be destroyed if the pile temperature does not reach 150–160°F. Most home compost piles — especially cold or passively managed ones — never get near that temperature. Which means composting a tomato plant with late blight, or squash with powdery mildew, or roses with black spot can reintroduce those pathogens directly into your garden beds through the finished compost.
The specific risk varies by disease. Some pathogens are killed relatively easily by moderate heat. Others — like Phytophthora infestans, the pathogen responsible for late blight — can survive in soil for years and devastate tomatoes, peppers, and potatoes across multiple seasons.
What to do instead
Bag diseased plant material and dispose of it in the trash or municipal green waste (where it will be processed at industrial temperatures). Do not bury it in the garden. The one exception: a reliably hot compost pile that you can confirm reaches and holds 130°F+ for several days can kill most common plant pathogens. If you don't actively measure your pile temperature, assume it doesn't get hot enough.
Category 3: Weeds That Have Gone to Seed
Most weeds are fine to compost — they're organic matter like anything else, and in a hot pile they break down without issue. The problem is weeds that have already flowered and set seed.
Weed seeds are remarkably resilient. Many common weed seeds survive temperatures that would kill most pathogens. If your pile doesn't consistently reach 145°F+, those seeds will survive the composting process and germinate wherever you spread the finished compost — introducing weeds directly into your most productive garden beds.
Iowa State University Extension specifically lists weeds that have gone to seed as a "don't" for home composting. The ADEQ compost guide echoes this: weeds are acceptable for hot piles only. Cold piles and passively managed piles should not receive seeded weeds.
What to do instead
Pull weeds before they flower and they're safe to compost. If they've already set seed, let them dry completely in the sun for several days (this kills many seeds), then add to the pile — still risky, but better than fresh. For certainty, bag seeded weeds and dispose of them in trash or green waste collection.
Category 4: Pet Waste and Human Waste
Horse, cow, chicken, and rabbit manure are excellent compost additions — they're nitrogen-rich and break down well. The rule changes sharply for carnivore waste.
Iowa State University Extension: do not add pet feces or spent cat litter to the compost pile. The reason is pathogen load. Carnivore waste (dogs, cats) can carry Toxocara roundworms, Toxoplasma gondii, Campylobacter, and other organisms that pose genuine health risks to humans. These pathogens require sustained high temperatures to kill — temperatures most home piles don't reliably reach.
Cat litter adds a second problem: most conventional cat litters are clay-based and don't decompose. Even "natural" or "biodegradable" cat litters often contain binders and additives that don't belong in a compost pile.
What to do instead
There are dedicated pet waste composters (like the Doggie Dooley in-ground system) designed specifically to process pet feces safely. The resulting material should only be used on non-edible ornamental plants, never on vegetable gardens. For cat litter, disposal in household trash is the standard recommendation.
Category 5: Treated Wood Products and Coal Ash
Wood ash from a fireplace or wood stove is fine in small quantities — it adds potassium and raises pH. Coal ash and charcoal ash are a different matter entirely.
Coal ash contains arsenic, mercury, lead, and other heavy metals that concentrate during burning. Adding coal ash to compost introduces these contaminants into your finished product and eventually into your garden soil. There's no safe quantity for edible gardens.
Pressure-treated lumber sawdust and scraps carry a similar concern. Older pressure-treated wood used CCA (chromated copper arsenate) treatment — the sawdust and decomposed material from this wood contains arsenic that persists in soil. Modern pressure-treated lumber uses different chemistry, but most composting guides recommend excluding all treated wood products from home piles as a conservative standard.
What to do instead
Wood ash from clean hardwood: fine to add in small amounts (a cup or two per turn, not a shovelful). Mix it into the pile rather than leaving it in layers — concentrated ash raises pH too sharply. Coal ash: trash only. Treated lumber scraps: check with your municipal waste program for proper disposal.
Category 6: Plants Treated With Persistent Herbicides
This one catches people off guard because the plant material itself looks perfectly normal — it's just grass clippings or garden trimmings. The problem is invisible.
Certain broadleaf herbicides — particularly those containing aminopyralid, clopyralid, or picloram — are absorbed by plants and can persist through the composting process. The resulting compost, when applied to susceptible plants (tomatoes, beans, peppers, carrots), causes distinctive cupping and curling of leaves, severely stunted growth, and often plant death. This phenomenon, sometimes called "killer compost," has damaged gardens across the U.S. when herbicide-treated grass clippings were composted and the finished material was used on vegetable beds.
The ADEQ compost guide recommends waiting at least three mowing cycles after any herbicide application before collecting clippings for compost.
What to do instead
If you're collecting grass clippings from your own lawn and you know it hasn't been treated, they're safe. If you're collecting from neighbors, golf courses, farms, or unknown sources, ask about herbicide history. When in doubt, leave them out — or add them only to a hot pile and test the finished compost on a few expendable plants before using broadly.
Category 7: Black Walnut and Eucalyptus
Most plant material composts safely. These two are exceptions worth knowing about specifically.
Black walnut (leaves, hulls, bark, wood) contains juglone, a naturally occurring compound that is toxic to many plants — particularly tomatoes, peppers, apples, blueberries, and rhododendrons. Juglone persists through composting and can damage susceptible plants when the finished compost is applied. If you have black walnut trees, keep their debris out of compost destined for vegetable or ornamental beds.
Eucalyptus leaves contain oils that inhibit decomposition and are toxic to earthworms. In small amounts they're not catastrophic, but a significant quantity of eucalyptus leaves can slow or stall a pile and reduce worm activity. If you compost eucalyptus, keep it to a small fraction of the total volume and expect slower breakdown.
The Gray Areas: Things That Are Technically Compostable But Cause Problems
These materials won't ruin your pile, but they're worth understanding before you add them.
Bread, pasta, rice, and cooked grains
Technically compostable, but they attract pests (especially rats) and can create anaerobic pockets as they break down in wet conditions. If you add them, bury them deep in the center of the pile — never on the surface — and keep the pile dry enough that they don't sit in moisture.
Large amounts of citrus peel
The citrus myth — that citrus kills beneficial microbes and worms — is largely overstated for regular compost piles, as covered in the fruit peel post. But large quantities added at once can temporarily lower pile pH and slow microbial activity. Add in moderation, chop before adding, and you won't have a problem. For worm bins specifically, citrus is genuinely problematic and should be avoided or kept to very small amounts.
Tea bags and coffee pods
Many tea bags contain polypropylene — a plastic used to heat-seal the bag — that does not break down in compost. The tea itself is compostable; the bag may not be. If you can't confirm your tea bags are fully natural fiber (look for "plastic-free" labeling), open them and compost the leaves only. Coffee pods (K-cups and similar) are not compostable — the plastic, foil, and filter are all separate materials that need to be separated before any component can be composted.
Glossy or heavily inked paper
Plain newspaper, brown cardboard, paper bags, and unbleached paper products compost well. Glossy paper (magazine pages, coated flyers, photo paper) contains clay coatings and sometimes chemical inks that don't belong in a compost pile. Shred plain paper and cardboard freely; skip anything glossy.
Dryer lint
Only safe if you exclusively dry natural fiber clothing (cotton, wool, linen). Most households dry synthetic fabrics (polyester, nylon, acrylic), and dryer lint from these loads contains microplastics that don't break down. If your dryer lint contains any synthetic fibers, it goes in the trash.
Quick Reference: What to Do Instead
| Keep Out Of Pile | Why | Do This Instead |
|---|---|---|
| Meat, fish, dairy, bones | Pests, odor, pathogens | Bokashi bucket |
| Diseased plants | Spreads pathogens to garden | Bag and trash |
| Seeded weeds | Seeds survive cold piles | Hot pile only or trash |
| Dog/cat feces | Human pathogens | Pet waste composter |
| Coal ash / charcoal | Heavy metals | Trash |
| Herbicide-treated clippings | Herbicide persists, damages plants | Wait 3 mowing cycles |
| Black walnut leaves/hulls | Juglone toxic to many plants | Trash or separate pile |
| Plastic tea bags / K-cups | Microplastics | Open and compost contents only |
Frequently Asked Questions
I accidentally added meat to my pile. Is it ruined?
Not ruined, but you need to act quickly. Dig the meat out if you can find it, then bury the remaining pile material under 6–8 inches of fresh browns (leaves, cardboard) to suppress the odor. If you can't retrieve the meat, turn the pile immediately, mix in a large amount of dry carbon material, and keep the surface covered. Pest pressure typically arrives within 24–48 hours of adding meat, so speed matters. A single small addition won't destroy the pile — it just requires quick management.
Can I compost moldy food?
Yes — with an important distinction. Moldy fruit and vegetables are fine. Mold is just early decomposition, and those organisms are part of the composting process. Moldy bread, pasta, and dairy are a different matter: the mold itself isn't the problem, but those materials attract pests when added to an open pile. Moldy grain-based foods should go into a bokashi bucket rather than an open compost pile.
What about compostable packaging labeled "100% compostable"?
Most "compostable" packaging is certified for industrial composting only — it requires temperatures and conditions that home piles don't reach. Adding it to a home pile usually results in material that doesn't break down, or breaks down into fragments that contaminate your finished compost. Unless the packaging is specifically labeled "home compostable" (a separate, stricter certification), treat it as trash or check if your municipal green waste program accepts it.
Can I compost paper with ink on it?
Plain newsprint and most cardboard: yes. Modern newspaper inks are largely soy-based and safe to compost. Heavily inked cardboard (bright colors, metallic inks) and glossy paper: avoid. The clay coatings on glossy paper don't compost and can leave a residue in finished compost. Shredded plain cardboard and newspaper are some of the best carbon sources available for a home pile — there's no reason to avoid them.
Is it safe to compost cooking oil in small amounts?
Very small amounts — like the residue on a paper towel used to wipe a pan — are fine. A greasy pizza box with most of the grease absorbed into the cardboard is generally acceptable, as the ADEQ compost guide notes. Large amounts of cooking oil are a different matter: they coat other materials and block microbial access, create anaerobic zones, and attract pests. Pour used cooking oil into a sealed container and dispose of it through your local household hazardous waste program or a used oil recycling service.
The Bottom Line
The "don't" list is shorter than most people expect. Meat, dairy, diseased plants, seeded weeds, pet waste, coal ash, and herbicide-treated clippings — that covers the things that cause real, documented problems. Everything else is either safe to compost or falls into a gray area where common sense and moderation apply.
When in doubt, ask one question: will this attract pests, spread disease, or introduce something that doesn't break down? If the answer is yes to any of those, leave it out. If the answer is no, it probably belongs in the pile.
Have you run into any composting mistakes that weren't on this list? Drop a comment — I'm especially curious about the herbicide-treated clipping problem, which seems to be happening more frequently as lawn care services become more common. It's one of the harder ones to catch before the damage is done.
— Ku
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