What Not to Put in Compost: 15 Items to Avoid (2026)

If you are wondering what not to put in compost, the short answer is meat and fish, dairy, cooking fats, pet waste, diseased or invasive plants, ash from coal and charcoal, chemically treated wood, and anything made of plastic, glass or metal. Each of these either spoils the pile, draws pests, or leaves toxins behind in the finished compost.

Most of these materials are biodegradable somewhere in the world. They are simply wrong for a cool backyard bin that a person has to live next to. A few are never safe anywhere, and a few are fine in a municipal facility that runs at 55 degrees Celsius or hotter. Knowing which category an item falls into saves you from throwing away food waste you did not need to toss.

I keep a backyard bin and a worm bin, and the biggest lesson from both is that almost every problem I have had came from one of the fifteen items below. The list follows how extension services and municipal waste agencies frame the rules, plus the practical workarounds that keep food waste out of the trash.

Table of Contents

1. What Not to Put in Compost at a Glance
2. 1. Meat, Fish, and Dairy
3. Meat, Fish, and Dairy: What Not to Put in Compost
4. 2. Pet Waste
5. 3. Cooked Oils and Cooking Fats
6. 4. Bones
7. 5. Egg Shells with Their Membranes
8. 6. Large Wood Chips and Pieces
9. 7. Sawdust from Treated or Painted Wood
10. 8. Yard Trimmings That Are Severely Diseased or Infested
11. 9. Blackberry, Poison Ivy, and Other Invasive Plants
12. 10. Rocks, Gravel, and Construction Debris
13. 11. Plastic, Glass, and Metal
14. 12. Styrofoam and Other Hard-to-Degrade Packaging
15. 13. Human Waste and Diapers
16. 14. Compostable Plastic Bags and Utensils
17. 15. Ash from Coals, Fireplaces, and Trash
18. Frequently Asked Questions
19. Can I put egg shells in my compost bin?
20. Are coffee grounds and paper coffee filters safe to compost?
21. What can I do with food scraps my compost pile cannot accept?
22. How do I know whether a material is compostable in a backyard bin?
23. Can diseased plants or invasive plants go in compost?
24. What are the signs that something has gone wrong with my compost pile?
25. What To Do First This Week

What Not to Put in Compost at a Glance

Here is the quick reference. Each item lists the practical problem it causes and the route that material belongs in instead.

Item	Why it is a problem	Where it should go
Meat, fish, seafood	Draws rodents and raccoons, smells	Curbside green cart if accepted, else trash
Dairy and cheese	Slow to break down, sours the pile	Trash, or a certified hot pile
Pet waste	Parasites and pathogens	Bagged trash or a local pet-waste program
Cooked oils and fats	Coats material and seals out oxygen	Drain with a paper towel, or trash
Bones	Very slow decay, attracts animals	Trash or a municipal drop-off
Whole eggshells with membrane	Holds residue, attracts flies	Crush clean shells and compost those
Large wood and branch pieces	Creates air pockets that dry the pile	Chip or shred before adding
Treated or painted sawdust	Preservatives and paint toxins	Construction waste route
Severely diseased or infested plants	Spores and pests survive a cool pile	Bagged trash or burn where legal
Invasive plants and berries	Roots and seeds regrow in the pile	Bag and take to an approved site
Rocks, gravel, rubble	No organic matter, damages equipment	Separate construction or masonry stream
Plastic, glass, metal	Never biodegrade, leave microplastics	Curbside recycling, correctly sorted
Styrofoam and foam packaging	Persists for decades, looks like food	Specialty drop-off where accepted
Human waste and diapers	Pathogens, engineered systems only	Trash, or a certified composting toilet
Compostable plastic bags and utensils	Needs industrial heat and collection	Only where your program collects them
Coal and charcoal ash	Heavy metals, alkaline ash	Trash, never the pile

1. Meat, Fish, and Dairy

Meat, fish, shellfish and dairy are the items people ask about most, and they are the ones most often left out of a cool home pile. Animal protein and fat break down slowly for the microbes working at backyard temperatures, so the material sits in the pile while everything around it finishes.

The result is usually a smell first and a pest problem second. Iowa State Extension puts it plainly: meat scraps, bones, grease, whole eggs and dairy decompose slowly, cause odors, and attract rodents. Raccoons and rats learn a compost bin quickly, and once they do, digging through it becomes a nightly event.

Meat, Fish, and Dairy: What Not to Put in Compost

Different systems have genuinely different rules here, and that is where most of the confusion comes from. A cool backyard bin, a tumbler, a worm bin and a municipal facility are four different systems with four different answers.

• Backyard bin and tumbler: leave out meat, fish, bones, dairy, cheese and grease. The pile does not get hot enough to handle them cleanly.
• Worm bin: the same items are out, plus more. Vermicomposting runs cool by design, and oily or sour food throws the bin off balance fast.
• Hot pile you manage carefully: a pile kept between 55 and 65 degrees Celsius can take meat and dairy, because thermophilic bacteria break them down fast enough to avoid the odor window.
• Municipal curbside organics: many programs accept meat and dairy because the material goes through a controlled, enclosed process. Check your own hauler’s list, because the rules are local.

So the rule is not that meat is uncompostable. It is that meat in a small cool pile that sits beside your house is a bad trade.

2. Pet Waste

Dog and cat waste should stay out of an ordinary home compost pile. Both can carry roundworm and whipworm eggs, along with bacteria such as E. coli and Salmonella, and a backyard pile does not reach the temperatures needed to kill them.

Manure from herbivores is the exception. Rabbits, guinea pigs, horses and goats produce manure that many gardeners compost routinely, though rabbit and guinea pig droppings are hot enough in nitrogen to want a good layer of leaves or straw over them.

For dogs and cats, bag the waste and put it in the trash, or look for a local pet-waste station or drop-off program. If you use a commercial pet-waste composter, follow its instructions exactly, including the activator powder it requires.

3. Cooked Oils and Cooking Fats

Cooking oils, butter, lard and grease coat everything they touch. A thin film over leaf material blocks the oxygen that aerobic microbes need, and the covered material eventually shifts to anaerobic breakdown, which is what produces the sour, rotten smell people blame on the bin itself.

Grease also repels the larger decomposers rather than feeding them. For small amounts, wipe the pan with a paper towel and throw the towel in the trash, or run warm water and a squirt of soap down the drain, which is safer for drains than a fat clog.

Do not pour oil down the sink in quantity. It solidifies in the sewer line. Small amounts in the green cart are usually fine, and many programs accept them for exactly this reason.

4. Bones

Bones take years to break down in a backyard pile, longer than anything else most people add. They also carry scraps of meat and fat that smell as they go, and the pile becomes a reliable food source for rodents and dogs.

They contribute very little to a typical home system. Calcium does not drive plant growth the way nitrogen, phosphorus and potassium do, so the trade is a multi-year wait for a nutrient your soil probably has enough of. Take small quantities to the trash and keep the pile focused on material that breaks down in a season.

5. Egg Shells with Their Membranes

Clean, crushed eggshells are fine in a compost pile. They add calcium, they break down reasonably well, and most extension services list them as an accepted item. Multiple discussions on r/composting make the same point: the shell is not the problem, the residue is.

Whole shells with the membrane still attached are the ones to skip. The membrane holds egg white and yolk against it, and that protein is a food source for flies and rats. Rinse the shells, pull or scrape off the membrane, crush them, and add them.

Cooked egg, yolk and whole eggs are a different category entirely, and they belong with meat and dairy for pest and odor reasons.

6. Large Wood Chips and Pieces

Branches, bark chunks and thick wood pieces break down over years, not months. While they sit there they create large air pockets, and a pile with too much of them dries out from the inside even when the surface feels damp.

That matters more than people expect. A dry interior is an aerobic problem waiting to happen: microbes slow down, the pile cools, and the balance tips toward odor. Run branches through a chipper first, or use a shredder on small material, and keep the pile turning so the big pieces get mixed down into the mass.

7. Sawdust from Treated or Painted Wood

Sawdust from pressure-treated lumber, painted or stained trim, or any wood whose coating you cannot identify does not belong in a compost pile. Preservatives such as copper-based compounds and paint pigments stay in the finished compost, and that soil is often the one you use on edible beds.

Clean, untreated hardwood sawdust is a different material. It is a useful brown, but it is very nitrogen-hungry, so mixing in a large quantity all at once can stall a pile. Add it in thin layers alongside greens, and use it sparingly.

8. Yard Trimmings That Are Severely Diseased or Infested

A plant hit hard by blight, rust, mildew or a fungal disease can carry spores that survive a cool pile and come back next season in the soil. Insect infestations bring egg masses and larvae that may also overwinter, and ants in particular will move a whole infested branch into your pile within a day.

This is a real problem reported repeatedly on home composting forums: diseased material goes in, the disease returns to the same bed the following year, and the compost gets blamed for it. Bag heavily diseased material and put it in the trash. Your local extension office can tell you whether a particular disease in your region has a specific disposal rule, and municipal green-waste programs sometimes restrict diseased material for the same reason.

9. Blackberry, Poison Ivy, and Other Invasive Plants

Invasive plants are excluded for a specific reason: they can regenerate from what you throw in. Blackberry canes root from a buried tip, so a five-inch piece of cane in the middle of a pile can produce a new thicket. Poison ivy roots from cuttings, and its urushiol oil is a serious problem for whoever handles the bag later.

Seeds are the other half of the problem. A cool pile rarely gets hot enough to kill weed seed, so a pile full of mature seed heads hands you the same weeds next season, now spread evenly across your bed. Bag invasive material, take it to an approved disposal site, and burn it only where local rules allow.

10. Rocks, Gravel, and Construction Debris

Rock, gravel, brick and concrete add nothing organic to the pile. They make it heavy, they reduce the volume of actual composting material in the bin, and they cause real damage to a tumbler’s blades and to mesh sifting screens.

Cement and lime products also raise the pH of the pile, which pushes it alkaline and slows decomposition. Handle construction and masonry material through your local construction, concrete or disposal stream, not through the green cart.

11. Plastic, Glass, and Metal

Plastic, glass and metal do not biodegrade. They are not slow. They are inert, and they stay in your finished compost as fragments that end up in garden beds year after year.

Glass grinds down into sharp particles that stay in the soil, and plastic breaks into the small fragments that turn up in garden soil and compost samples. Aluminum and steel corrode slowly and can carry coatings. None of this makes a pile unusable, but none of it makes the material worth adding. Sort it into curbside recycling instead, and check local rules on what actually goes in the bin, since the accepted list changes.

12. Styrofoam and Other Hard-to-Degrade Packaging

Expanded polystyrene foam and rigid foam packaging sit in a backyard pile essentially unchanged. In a landfill it persists for decades, and researchers keep finding foam fragments in soil and water long after the material was discarded.

It also causes an immediate problem in the garden. Foam is light, white and irregular, and animals read it as food. Raccoons and gulls will pull a whole pile apart to get at it, which spills the contents of your bin across the yard. Keep foam out and use a specialty drop-off program where one exists in your area.

13. Human Waste and Diapers

Human waste, diapers and used hygiene products do not go in a home compost bin. The sanitation requirements are real, and a backyard pile does not meet them, which is a different thing from saying the material cannot be composted at all.

Certified composting toilet systems and managed biosolids programs are designed for this material and handle it under controlled conditions. Diapers and sanitary products go in the trash, and if a local program collects diapers or human waste, that is the route to use. A worm bin is not an option here either.

14. Compostable Plastic Bags and Utensils

Items labeled compostable are the most genuinely debated category on this list, and the honest answer is that most of them belong in the trash for a home composter. PLA, the material in most compostable bags, cups and utensils, needs controlled industrial temperatures and a specific collection stream. It does not break down in a backyard bin in any useful timeframe.

The practical rule is simple: if your curbside program does not specifically collect certified compostable packaging, it goes in the trash. If it does, follow those instructions. Some areas have drop-off collection points for certified compostable bags, and those are the only reliable way to recycle them.

There is a test that helps more than the label. Break the item and look at the cross-section. If it is paper, it composts. If it is plastic that was simply thinner, it does not, no matter what the printing says.

15. Ash from Coals, Fireplaces, and Trash

Coal ash, charcoal briquette ash and ash from burned trash should never touch a compost pile. Coal ash carries heavy metals, and briquettes contain a petrochemical accelerant that burns off incompletely. Ash from a mixed trash fire can carry anything that was in the fire, including plastics and treated wood.

They are also strongly alkaline, which pushes the pile’s pH up and slows microbial work. A small amount of clean, cold wood ash from a fireplace is the one exception, and even then most composters skip it because the limestone and metal content is more than a typical garden bed needs. Put the rest in the trash and let it cool completely first.

Frequently Asked Questions

What To Do First This Week

Start with the green cart. Most curbside organics programs in the US take food scraps, and a few take meat and dairy, so the pile you thought you had to protect may have a municipal alternative you have not used. Check your hauler’s accepted list, then move your food scraps there and keep the home bin for the things a backyard pile handles well.

Once that is settled, fix the ratio. Aim for roughly 30 parts carbon to 1 part nitrogen by volume, bury food scraps in the center of the pile, and cap them with a few inches of shredded leaves or plain cardboard. Those three habits solve most of the odor, fly and rodent complaints people post about, and they cost nothing.

Knowing what not to put in compost is the easy half. The other half is having a route for the material you are excluding, so nothing ends up in the trash by default.