Gardening & Homesteading

10 Things You Should Not Put In Your Compost Pile

While technically you can compost anything that was living, for better compost and less hassle, here are 10 things you should not put in your compost pile.

Composting is one of the most powerful things you can do for a sustainable planet—even if you don’t have a garden. We simply cannot continue to take nutrients from the soil to grow food, year after year, and not put them back in equal or greater measure, and expect the soil to continue to provide for us.

There are at least 100 things in your home that you can compost, which will greatly reduce the amount of trash you put out every week to go to the landfill. But even though technically you can compost anything that was once living, some things are better left out of the compost pile for the sake of better compost and less hassle.

Here are 10 of them…

1. Dog and Cat Poop

Horse, cow, chicken and rabbit droppings are great additions to your compost pile. They will add nutrients and organic matter that will benefit your soil. However, it is not advisable to add the poop from dogs and cats (and other carnivores) to your compost. Their waste often contains microorganisms and parasites that you do not want to introduce to the crops you will be eating.

If you do want to compost your dog and cat poop, you must process them separately from your regular compost pile (there are special composters just for pet waste), and only use the resulting compost on non-food crops.

Find composters made for pet waste.

2. Tea and Coffee Bags

Coffee grounds and tea leaves definitely belong in a compost pile. They provide generous amounts of nitrogen, phosphorous and potassium, which are elements that are essential to plants. However, coffee grounds and tea leaves should only be added to compost if they are bag-less, or have been removed from their bags.

The bags that some coffee and tea products come in contain synthetic fibers that do not break down in a compost pile, and can contain chemicals you don’t want in your soil.

Don’t compost tea or coffee bags unless you are certain they are made from natural materials, like cotton or hemp.

3. Citrus Peels and Onions

While fruit and vegetables scraps from the kitchen are fundamental ingredients in a home compost pile, there are two iffy exceptions: citrus peel and onions.

“What?!” you say? Unfortunately, the natural chemicals and acidity in citrus peels and onions can kill worms and other microorganisms, which can slow down the decomposition in your pile. Plus, unless you chop them into tiny bits, citrus peels take forever to break down, which will delay how soon you can use your compost.

If you only occasionally throw citrus peels and onion scraps into your compost bin, it’s no big deal, but if you vermicompost or have worm bins (which is an amazingly convenient and odor-free way to compost if you are in an apartment), then citrus peels, onions and garlic scraps are a no-no, because they will harm your worms.

(Personally, I usually put my onion scraps into the freezer to use when I make stock, and use citrus peels to make non-toxic DIY house cleaning sprays instead.)

4. Fish and Meat Scraps

While technically they will decompose just fine, you really don’t want to add fish and meat scraps to the compost pile. Fish and meat are organic and will add nutrients to your garden, but unfortunately their smell will act like a magnet for any rats, mice, foxes, raccoons, or cats in the neighborhood (or even coyotes and bears, depending on where you live), who will ransack the compost to eat them.

The stink of rotting meat and fish could also really annoy you and your neighbors, too!

5. Glossy or Coated Paper

Many paper products are potential compost fodder, especially soy-ink newspapers, old paper towels and tissues and even shredded cardboard. They are from trees, after all!

However, paper that has been treated with plastic-like coatings to make it bright, colorful and glossy, like magazines, won’t decompose properly, contains toxins, and is not appropriate for your compost pile.

6. Sticky Labels on Fruits and Vegetables

Those obnoxious little sticky labels and price tags on fruit and vegetables are made of “food-grade” plastic or vinyl, and do not biodegrade. (See Glossy Paper, above.) They are also easy to miss, which means they often end up trashing up your compost piles.

Municipal composters can’t handle them, either. In fact, at least one waste management company says PLU produce stickers are their biggest source of compost contamination.

Try to remove these stickers from fruit and veggie scraps before you put them in the compost pile.

7. Coal Fire Ash

The ash from coal fires or charcoal-briquet fires should not be added to your compost pile, as it contains so much sulfur as to make the soil excessively acidic, which will harm your plants. Also, many charcoal briquets are treated with chemicals you really don’t want in your compost, your garden or your food.

Wood fire ash from the fireplace can be added in moderation, but please put the coal and charcoal-briquet ash in the trash bin.

8. Sawdust From Treated Wood

While sawdust from untreated, natural woods can be a great addition to compost, if the wood has been treated with any kind of pressure treatment, varnish, stain or paint, you should never add the sawdust to your compost pile.

These toxic compounds won’t break down in the composting process and can get into the soil, negatively affecting microorganism activity and plant health. The sawdust from pressure treated wood alone contains arsenic and cadmium—two toxins you definitely don’t want in your garden or your food!

Sawdust from treated wood also takes a very long time to break down because it is protected from decay by the chemicals put on it, which will delay how soon you can use your compost on the garden.

9. Large Branches

Large branches take forever to break down and will greatly delay your ability to use your compost in the garden. It may be a little extra work to cut down or chip your branches for the compost pile, but the smaller the pieces you add to your compost, the faster they will break down.

Alternatively, you can start a branch pile at the back of your lot, where you simply pile branches and let them rot over the course of a couple of years. Branch piles also make great habitat for small creatures and snakes too, so be aware of your local fauna before you start one.

10. Synthetic Fertilizer

Synthetic fertilizers (like the blue Miracle stuff) introduce high levels of inorganic elements into the garden ecosystem. Like taking a generic multivitamin instead of eating real, whole food, the form in which these synthetic fertilizers provide nutrients to the soil can actually kill the microorganisms in your compost and your soil, which will ultimately affect the health of your plants.

Compounds in synthetic fertilizers, such as heavy metals, will also leach through the soil into the water table, as well as upset the natural balance of nutrients in the soil and increase salinity.

Stick to natural ingredients for your compost pile.

Image: franz pfluegl/iStock/Getty Images

This article was excerpted from my book Sustainability Starts at Home – How to Save Money While Saving the Planet.
As an Amazon Associate I earn from qualifying purchases.

About the author

Dawn Gifford

Dawn is the creator of Small Footprint Family, and the author of the critically acclaimed Sustainability Starts at Home - How to Save Money While Saving the Planet. After a 20-year career in green building and environmental sustainability, chronic illness forced her to shift her expertise and passion from the public sphere to home and hearth. Get the whole story behind SFF here.

78 Comments

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  • Are the blues used in cardboard and correlated card toxic in wormeties and home compost bins. I don’t want to make my own compost then find out I’ve been putting nasty stuff into my garden and crops.

  • I have a question: how do you shred things like toilet paper rolls, paperboard packaging such as cereal boxes, etc.? Thanks in advance!

      • I’m thinking cereal boxes should not be composted. cereal boxes, along with boxed food items tend to have a semi-glossy finish. I especially am thinking milk cartons would fall under the “do not compost” rule.

        • I think it depends on the cereal, so err on the side of caution. There are many brands of cereal these days using uncoated boxes, and most inks used these days are soy-based anyway. Milk cartons are usually just waxed with food-grade wax, so they will compost, but it will take much longer. Best to thoroughly shred those.

  • Hi, is it better to put fermented meat (from Bokashi bin) into compost? Will this help the problem with smell and insects? or is this still not recommended?

    • Any animal product will draw insects and rodents, and begin to smell terrible as it breaks down. If you can control for the critters, and don’t mind the smell, you can compost any biological product, including meat.

  • This spring I had a tree fall due to a tornado. I partially filled the hole with dog poop. My dogs take a heartworm/intestinal worm preventative. I have a volunteer cherry tomato thriving on that spot. Are the tomatoes safe to eat?

  • Hello. I am new to composting, and I put a few burned charcoal pieces in my pile early on. Having just found out that it was a bad idea, should I start new?

  • I’m using my kitchen waste to decompost. When I first started I added a piece of cooked chicken that created a certain type of worms (not the soil worm) is like a whitish chubby worm. Are those worms bad for my decompost?

  • I’ve been discussing with a friend why they should not put weeds into the compost bin. They disagree. What is your take on it?

    • If the weeds are seedy, or reproduce by stolons (like bermuda grass), I would leave them out of the compost unless you are certain your compost pile gets hot enough to kill these seeds/plants. Otherwise, you are likely to just make more weeds in your garden. If the weeds are not seedy, or do not reproduce along the roots, then definitely compost them!

  • This is really great, straightforward information. Thank you, Dawn 😀 I’m really excited to learn how to compost this year and move towards a Zero-Waste life.

  • Great list, Thanks!!
    You mentioned Cardboard and wood. But many cardboards and wood products have anti flammable and even petroleum based binders. So I remain skeptical.
    We get some much of this in mail order products these days.
    I often burn these in a back yard oven and would love to compost the ashes ( mixed in and in appropriate levels)

    What are your thoughts on cardboard ashes?

    What are your thoughts on ashes from commercial charcoal?

    thanks!

    • As the post states, I would not use ashes from commercial charcoal, because those briquettes are high in sulphur, and often contain all sorts of toxic stuff, including heavy metals. Cardboard is usually better recycled with other paper, but it is also really great for sheet mulching. If you add it to compost piles, it needs to be uncoated, corregated, and well shredded.

    • No and yes. All organic matter will decompose, in time, however if you have too much “green” or nitrogenous matter in your compost pile, it will become imbalanced, which could lead to a smelly, anaerobic, acidic breakdown, instead of a nice rich, crumbly humus. So make sure whatever you are putting in to the compost pile, that you are balancing your carbon/browns with your nitrogen/greens. More info on that here.

    • If they are made of 100% paper, and totally empty, they can be composted. Just be sure to shred them into bits before putting them in. They would be considered a “brown” or carbonaceous ingredient.

      • Interesting post. However, David The Good DOES compost meat, fish and poultry successfully. I’d be dealt interested to hear you two debate this! He has written several books, has a YouTube channel, and is often featured on The Grow Network.

  • Enjoyed this article!
    From experience I’ve found that lettuce grown in compost that contains coffee grounds tend to be bitter, so I grow my lettuce in a small area of my garden that is “coffee-ground-free.” ~ I used to place the coffee filters on top of the compost pile for a couple of days to let them dry out, shake the coffee off of the paper filters then throw the paper away (until my sister told me that I can compost the paper filters!) Now, instead of throwing out the filters, I still let them dry out, but I place them around the base of some of the vegetables, as a weed-block under the straw that I use to mulch the garden. Works well,,, and when all veggies are picked, I simply turn the filters into the ground (by that time they are pretty much deteriorated anyway). ~ Last comment is,,, last 3 summers I have purchased a small container of night crawlers from a local store that sells bait for fishing,,, set them free in my compost pile and they pay me back for my kindness by working their little tails off in my compost!
    Win/Win!

  • Sunflower seeds should not be composted because , according to the Wild about Birds MN D N R book they are treated with a growth inhibitor The book goes on to say that you should not put them in Flower beds, Gardens or Compost .

    • This only applies to hulled sunflower seeds like those used in bird seed, which are not treated with growth inhibitor but actually contain natural growth inhibitors to protect them from competition, much like walnuts do. If you are eating roasted or hulled sunflower seeds, feel free to compost them in your regular compost pile.

      However, put regular sunflower hulls into your brush pile at the back of the property, where it can get more time to break down. Composting will eventually decompose both the shells and the growth-inhibiting chemicals, but it will take too long for your regular pile.

  • I been composting for years using vermiculture and I do understand your points regarding tea bags, citrus and onions, but I have been composting them without a problem and have a very healthy worm population. I’ll agree that those items may not be good to add but they make such a small percentage of my pile they do not seem to have a significant effect. They probably make up <2% of the pile which is mostly leaves, grass clippings, and organic plant waste.

    • If these things make up a small portion of your compost, as they do for you, that great. But for indoor and small-scale vermicomposters, they might only be composting food, therefore citrus, onions, etc. can make up a significant percentage of the compost, and would be of harm.

    • They decompose, too! It’s more important to return organic matter to the earth than ever before–ALL organic matter. Compost microorganisms can break down pesticides, but if you are concerned, use the humus from your pile to fertilize trees and other non-edibles.

    • If the tea bags are made of nylon (plastic) as many brands are, then no, they can’t go in the compost.

      As explained in the article, orange and onion peels will break down in compost for sure, but they will do so at a much slower rate than your other food scraps, and they will be noxious to the worms in your pile, which will avoid them. This is why I recommend leaving them out, or composting them separately in a “slow pile.”

  • We use a product called Burnout which is 8% clove oil and 24% citric acid (applied as a 25% aqueous mix) to kill weeds. Several days after spraying the weeds, there is still some clove oil odor, but the dead leaves are dry. Can material sprayed with this mix be included in a large community-based compost endeavor? Or, should we avoid adding this material to the bins,so as not to affect the composting process?

    • You’ll need to contact the community compost operation and ask them what they can take. Each municipality will have different standards based on factors such as locally available inputs, staff expertise, size of operation, etc.

  • What about mushrooms/fungus growing around the yard? Most of the mushrooms that pop up after a rain, I leave alone to go back into the lawn but we get some monster fungus around our fence that is kind of smelly and gross so I scooped it out from the fence and chopped it with the shovel blade and mixed into our compost. It’s definitely an “organic” product, but I’m curious if this type of fungus is harmful to the worms in our compost? Any thoughts on the matter?

  • I have had occasion to spend some time in a hospital (husband got knocked into a pole by a hit and run driver)…. In the dining room they ‘compost all paper towels, cooked foods meat, bone left overs etc… I had been led to believe that cooked food, meat and bones are not good for composting. What do they do with this stuff and would you use it?
    Karen

    • Anything organic can be safely composted, but not necessarily by the home composter. Composting animal and seafood products can draw animals, and has to be done in a controlled environment where high temperatures and proper aeration can be maintained. This is not typically one’s backyard compost pile.

      Once properly decomposed, the resulting humus can be used almost anywhere. You’ll have to ask the hospital where they use it!

  • For your citrus and onion peels, meat, and fish, you can burn them in your fire pit with your untreated wood. Save the ashes in a metal trash can. Add a scoop when you are turning your compost to make sure it mixes loosely and liberally. (Do not burn and add bones to your ash stock)

  • You said the problem with coal ash is it can become acidic. So, if I want acidic soil (like to put around blueberries), then would coal ash be beneficial? Is there any other reason to avoid it?

    • No! You do not want to use coal ash to acidify your garden as it contains toxic petrochemicals! It shouldn’t go in compost or in your soil. You can add some firewood ash to your compost, where microorganisms will break it down, but it is generally too strong for the garden straight. Better to get some horticultural sulphur to acidify for blueberries. You can also use peat moss in the soil, and pine needle mulch to help acidify for blueberries.

      • I had put the coal ash into the compost before I read this article, It wasn’t a big amount so what should I do , Do I need to clean out the compost bin and start over again ? Thank you for any respond

        • Add in organic matter till the pile is at least 3x3x3 feet in volume and then let it compost till it’s done. I would only use that compost around trees and other non-edibles. Meanwhile, start a new compost pile for your veggie garden.

  • Can I put moldy bread in my compost? Everyone I’ve consulted have had a different opinion about it. I just really need some clarity,

  • Do you add worms to your compost bin? I have the same one. Do you use compost starter? I just started using mine two weeks ago.

  • I’ve never had trouble with domestic quantities of onion, garlic and citrus. Is this only a worm farm issue? My compost is full of worms

    • “If you only occasionally throw citrus peels and onion scraps into your compost bin, it’s no big deal, but if you vermicompost or have worm bins, then citrus peels, onions and garlic scraps are a no-no, because they will harm your worms.”

  • I really like to fish and after we eat some, we put the remains in the compost. I use a shovel to dig down deep in the pile, put in the fish remains, and refill the hole. We have racoons, cats, and lots of foxes in our area, but haven’t had a problem with anything digging up the compost to get to the fish remains. We’ve done this for three years, I think.

    I’m not suggesting anyone do this, but it has worked for us. We have a fairly large compost pile and maybe it’s enough to cover the fish scent. I’m not sure.

    • I don’t compost the scraps from my stock because they are usually covered in meat juice, collagen and fat. But if I were making vegetable stock, I would compost the scraps, including the onions—unless I had worm bins. Onions are always harmful to worms.

          • I am just starting my compost in a garden container/tower that has the compost shoot in the center and you grow plants all around it in layers. Is there something I should be adding to the shoot/compost before I add my worms? I have basic good house hold garbage; lettuce, celery. some plant cuttings, potatoes, carrot peels, tomatoes, etc. I did add a little onion, but not much and won’t do that again after reading this! And was going to add citrus but will not do that 🙂 I have also added some leaves. This shoot is not very large, about 6″ in diameter and about 4′ or so tall.

            Can I put house plant trimmings, such as Creeping Charlie?

            Thanks for your help

          • I’m not sure what Creeping Charlie is, but you can certainly put houseplant trimmings into the pile. The exception would be for vining and tropical species that would be more likely to take root and grow in your pile than decompose.

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