What’s Not Compostable? 33 Things You Can’t Compost At Home
We’re crazy about composting, and good on you for taking up the challenge with us. Composting is just about one of the most impactful ways to reduce global waste.
And, you don’t even need a backyard to do it!
A quick recap: composting is nature’s way of breaking down organic waste, or waste of biological/organic origin. Think plants, not plastic.
The process yields a substance known as humus, a nutrient dense chemical-free fertilizer and pesticide which can be returned to the earth. Essentially, composting creates a never ending loop which allows us to give back, rather than just take from the planet.
For more info on how it all works and to see a detailed list of all the things you can compost, read our article on What is Compostable.
Not everything is compostable.
As magical as composting is, it’s not perfect.
Sometimes we need to help it be its best by keeping a few things far away. It’s like purging your fridge of ice cream when you’re on a diet.
Putting the wrong item in your compost bin may not only lead to inefficient biodegradation, but also contamination of the whole heap. A waste of all that waste!
Don’t get us wrong: we absolutely want you to compost as much as possible. The alternative is having organic waste go to landfills and decompose anaerobically into methane gas (a huge contributor to climate change).
So as you read through this list of things you can’t compost, think about how you can avoid wasting those items. Either refuse them altogether or find other ways to reuse and recycle, as we give some suggestions for how to do it.
WHAT NOT TO COMPOST FROM THE KITCHEN
1. Meat, fish, and bones: This is probably the biggest “composting don’t” as far as food goes. A few specialized high tech composters can handle these items but your run of the mill compost pile or Bokashi bin can’t. Worms can’t eat these items either.
Essentially, meat products raise your compost’s temperature which causes it to stink. And anything that stinks, of course, will attract unwanted pests, like raccoons, rodents and maggots.
2. Dairy and eggs: As dairy products break down and ferment, they’ll also start to smell. Like REALLY smell. Like rotten eggs and sour milk smell! Which pests and scavengers love.
3. Butter, cooking oil, animal fat, and grease: Oil and water just don’t mix. Since moisture is a key component to the composting process, these items will not break down. Instead they’ll shift the moisture balance of your pile and attract pests.
4. Fat based condiments and foods: Things like oily salad dressing and peanut butter will not break down any better than straight-up fats for the same reason as #3.
5. Citrus fruit peels: Aside from taking a long time to break down, the acidity in citrus fruits can easily throw off the pH of your compost bin and slow the overall decomposition. If you have a vermicomposter, these are especially forbidden because they can kill your hardworking worms.
You can put these to use by soaking them to make your own DIY cleaning products.
6. Onions and garlic scraps: As with citrus peels, these can kill worms and other microorganisms essential for breaking down organic matter.
Instead, plant your onion scraps to grow them into new bulbs.
7. Baked goods and cooked grains: No rice or fresh baked bread products, especially confections with glazes or high sugar content. Both breed bad bacteria and attract rodents. Cooked rice is especially notorious for growing bad bacteria in a compost pile.
Plain bread that’s stale and hard (which is the only type of bread you should compost), and uncooked rice and pasta CAN be composted in moderation. Also, be sure to bury it as deeply as you can.
8. Coffee pods and tea bags: While coffee pods are a pretty obvious no-no, tea bags may seem harmless. But they’re not. Many are made of food grade PET (aka plastic) or preservative nylon fibers that at best will not break down, and at worse contaminate the whole pile.
Coffee grounds and tea leaves alone are great sources of nutrients for compost, so definitely remove them from their bags and pods.
Or better yet, switch to loose leaf tea and moka pot / french press coffee altogether, both are zero waste and won’t put you at risk of drinking melted plastic (which studies have shown to cause reproductive issues).
And while we’re on the subject of bags be sure to read up on compostable and biodegradable trash bags before you toss them in the worm bin or compost heap. They’re often not as green as they say they are.
9. Stickers on fruits and vegetables: These bits of plastic are easy to miss, but make sure you peel them off before tossing that banana peel in your pile. They can’t even break down in industrial composting facilities, let alone your home one.
In fact, they’re e actually a huge source of composting contamination all over the world. We’ve mostly managed to eliminate our consumption of these annoying stickers by buying directly from the farmers
10. Coated cardboard packaging: Any food packaging with either a plastic or foil layer is not suitable for your compost pile. This means waxy lined paper cups, milk cartons, and juice boxes, and foil-lined paper snack cracker and cookie bags. Takeaway coffee cups are generally not compostable (or recyclable!)
11. Bioplastic packaging and cellophane: Beware of any “biodegradable packaging” unless you know for a fact that it’s certified to be home compostable. Many of these are only compostable in industrial composting facilities (which get far hotter than your home compost pile).
WHAT NOT TO COMPOST FROM THE YARD
12. Large branches or pieces of wood: These take forever to break down. Chip first.
13. Coal ash: No charcoal from the grill. While wood ashes are safe to mix into your compost pile, coal ashes are not. They contain levels of sulfur and iron which are high enough to damage plants.
14. Naturally toxic plants: Avoid Oleander leaves and anything from the black walnut tree (including walnuts themselves), which contains juglone, a naturally toxic compound for plants.
15. Treated lumber: Any lumber intended to be used as building materials are usually treated with water repellant which contains toxic chemicals. Plus, these chemicals will make them more resistant to moisture and thus biodegradation. They’ll take a very long time to break down.
This includes sawdust from treated wood. Sawdust from chopping firewood: okay to compost. Sawdust from your home construction project: not okay to compost.
16. Tomato fruits: Tomato plants and trimmings are fine, and technically, the fruits are fine, too. But they will lead to baby tomato sprouts anywhere you use the compost. Instead, use your overripe tomatoes to make some yummy salsa!
17. Synthetic fertilizer: Don’t dump remnants of fertilizer or even soil recently treated with large doses of it in your pile. Synthetic fertilizers may do a few things to compost: kill microorganisms (slowing down the pile’s decomposition rate), alter the pH and nutrient levels and eventually leach into the ground.
18. Lawn trimmings recently treated with pesticides or herbicides: Lots of grass has some degree of chemical treatment. The composting process is pretty well suited at breaking those materials down harmlessly, but only in small amounts. And since lawns are typically treated in high concentrations, a freshly treated lawn shouldn’t go near your compost until the concentration has had time to weaken and dilute. Give it a few weeks.
19. Diseased or insect infested plants: Plants that have died because of disease/fungal infection or insect infestation aren’t good compost material. Unless your composter gets really hot (meaning it’s operating at maximum efficiency, which is unlikely), there’s no guarantee these things will be killed. If they’re not, you could spread the blight with your compost.
20. Weeds gone to seed and invasive plants: Dandelions and ivy, for example, are persistent buggers that will simply sprout in your compost pile and spread to wherever you use the compost.
21. Cigarette butts: Some are made of plastic, but that aside, cigarettes are filled with chemicals. Straight tobacco is compostable but unfortunately, that’s not all that’s in cigarettes.
WHAT NOT TO COMPOST FROM THE BATHROOM
22. Synthetic soaps: Soaps shouldn’t go in your compost, unless they’re certified as biodegradable (and thus safe for the environment). Even if you have a tiny sliver of standard bar soap left over, you’re better off to collect it and once you have a few, melt them together to make a new bar.
23. Used feminine hygiene products: No pads, tampons, or even cardboard applicators. Anything with blood can contain hard-to-kill pathogens which can be transferred to your compost. You can compost reusable cotton liners but only if they’ve been thoroughly washed.
24. Humans feces and diapers: Like blood, human feces poses a major health risk, and can contain diseases and parasites. Keep your poo in the loo and not on the lawn.
As with reusable liner pads, reusable eco friendly diapers and nappies can be composted (provided they’re made with 100% natural fabrics) and as they’ve been washed.
WHAT NOT TO COMPOST FROM THE CLOSET
25. Vacuum cleaner contents: The tiny plastic or synthetic fibers that carpets constantly shed could contaminate your compost (as well as the odd price tag connector or LEGO piece that gets sucked up).
26. Dryer lint: For the same reason as #25, dryer lint contains an amalgamation of various fabrics (and even from past loads). So even if you only dry 100% cotton clothing in a separate load, the lint could still contain synthetic fibers from other garments that have been in the dryer.
27. Synthetic fabric of any kind: These contain all sorts of harmful chemicals and dyes. Even if your t-shirt is 99% Cotton and just 1% polyester, it can’t be composted. The smallest amount of these fibers can ruin a compost batch.
28. Leather goods: This means worn out belts, wallets, purses gloves etc. Though just make sure it’s not vegan leather (i.e it’s organic), it can takes years to properly decompose, especially since most leather accessories are treated with life-extending materials.
Try to find other clever ways to reuse these instead – maybe they can still be donated to a non-profit or thrift shop. If not, you might be able to use the leather scraps yourself to make an eco friendly gift.
WHAT NOT TO COMPOST FROM THE OFFICE
29. Paper with lots of color printing or Sharpie drawn inks: Colored printer ink and markers such as Sharpies can contain heavy metals and other toxins. Anything saturated with these can contaminate your compost.
30. Glossy Paper: Any paper that has a glossy, plastic finish is toxic to your compost pile. This unfortunately means some magazines, product catalogues, wrapping paper and photographs.
WHAT NOT TO COMPOST FROM PETS & ANIMALS
31. Dog and cat feces and litter: Carnivorous / omnivorous animals’ intestines can be host to a wide range of resilient parasites and pathogens. This type of feces must be composted separately in special, high temperature pet composters (more about this in our zero waste dog article).
Manure from other pets or livestock, however, is very beneficial.
32. Manure from sick animals: Herbivorous or not, any sick animal can pass on bad bacteria and viruses through their excrement.
33. Dead animals
FINAL THOUGHTS ON WHAT IS NOT COMPOSTABLE
We hope this list, together with our list on what you can compost is helpful for you in keeping your compost alien free. But when in doubt, leave it out.
Nothing says “compost buzzkill” like a little contamination that ruins all your good, well-intentioned work!
If you found this article useful, consider sharing it to spread the word about how amazing composting (done properly) can be for the planet.
And don’t let your lifestyle fool you; composting is for everyone.
As this article sums up nicely, “you would be amazed at what you can do with just a small space.”
Feel free to reach out to us with questions about what you can and can’t compost, how to start a backyard compost pile or how to get into apartment composting.
It’s easier than you think!