Composting Cooked Veggies: The All-Important Do’s and Don’ts


Our garden in July 2019 with compost and fruit trees in the background. Foreground includes portable chicken run

Having our own compost bin has been a great way to put food and other waste to better use – by turning it into rich, garden-improving mulch. But when we first started, it was easy to get lost wondering what could (or couldn’t) be put on the compost pile. Can you compost cooked vegetables?

Cooked vegetables can be composted if they weren’t cooked with pest-attractants like oils, sugars, sauces, or animal products. Cooked veggies rot quickly, are nitrogen-rich, and need a carbon-based additive (to aid in the breakdown and prevent the compost from reeking and attracting pests).

Keep reading to up your composting game – without adding any rotten stink (or extra vermin) to your garden.

Can You Compost Cooked Veggies?

Cooked vegetables can most definitely be composted. No matter where you put them, they’re going to break down and decompose. However, the real question is this: do you want that particular, cooked vegetable to compost in your backyard compost bin? Or would it be safer (and less smelly) being disposed of in another manner?

If the vegetables were cooked in a sauce, oil, sugary base, or animal product (like meat or fat), they would be stinkier and more likely to attract disease-ridden pests (like rodents or flies). So if you don’t want something digging up your compost bin, don’t put anything with oils, sugars, fats, or animal products into your compost. That includes cooked veggies!

Plus, those particular items (oils, fats, sauces, and animal products) don’t compost as well (or safely) without extra steps (that can get pretty involved). As such, it’s usually safer to avoid them. We avoid putting those into our compost bin – we don’t want pests or the diseases they carry! These pests also carry parasites – and we don’t want those parasites getting a foot hold in our backyard homestead.

However, if you’re a fan of steaming or cooking your veggies without oily additives, they can most definitely be added to your compost. Adding plant-based seasonings (or even a pinch of salt and pepper) isn’t a big deal, either. Those can be composted fine, provided it isn’t drowning in salt. Too much salt will kill your compost – and your garden.

In any case, once you’re ready to compost your cooked, oil-free veggies, then your main concern is going to be maintaining your carbon-to-nitrogen ratio. Thankfully, there’s a pretty easy way to maintain your carbon/nitrogen ratio for better composting and breakdown into a rich, earthy-smelling soil or mulch. It’s this: do both a smell test and a heat test.

  • The smell test is easy. Compost shouldn’t reek. If it does, it has too much nitrogen. Add some brown (carbon-rich) material to your compost to fix the smell. Common browns include leaves, paper shavings, wood shavings, or pine shavings.
  • The heat test is also easy. Compost needs to get hot enough to break down into mulch and soil. It doesn’t need to be burning hot or about to catch fire. It just needs to be hot enough to be a stink-free steamy. Otherwise, there isn’t enough nitrogen (or microbial activity) to break down the material. Add some more greens (grass clippings, fruit and veggie waste, or chicken manure) and water to re-start the decomposition process.

Want to know of other ways to properly dispose of those veggie dishes that do have a bit of oil, animal product, or some types of sauces on them? Make sure you read to the end of this article – I’ll give you some specific ideas on how to handle those veggie dishes without throwing them into the trash.

Can I Compost Cooked Food Waste?

Most food waste can be composted, as long as it’s plant-based and free from oils, fats, sugars, and animal products. However, if it’s going to attract pests (insect, mammal, parasitic, fungal, or otherwise) that you’d rather avoid, then it may be best to skip adding that particular type of food waste to your compost pile.

Even if you’ve got an enclosed bin, you’re going to want to avoid most of those same foods still. An enclosed bin may keep larger pests from getting to the chunks inside, but they leak. And you’d better believe that the oils, sauces, and even some of the animal products will leak out and attract pests.

Even if your food isn’t compost-friendly, that doesn’t mean you automatically need to throw it in the trash. There are other, homestead-friendly options. We’ll get there, I promise.

Can I Compost Cooked Potatoes?

Cooked, plain potatoes can definitely be composted. This holds true if they’re baked, cooked, steamed, roasted, or boiled. You can compost the peel, the insides, or all of the above. If you’ve added a little bit of plant-based seasonings (like herbs), they’re still safe for your compost bin.

However, if you’re frying those taters in oil, then they aren’t ever suitable for composting. They’re too oily and will need to be disposed of in other ways.

But let’s get back to our not-fried potatoes and composting them. They’re definitely safe as plain potatoes. But once you add certain fixings, then that cooked potato isn’t suitable for the compost bin. Here are some of the most common, “not for the compost bin!” potato fixings.

  • Butter
  • Sour cream
  • Bacon bits – unless they’re the “fake” or TVP (textured vegetable protein) bacon bits. Then that might not be a problem in super-small quantities.
  • Gravy
  • Meat
  • Cheese sauces
  • Cheese

Again, these are all items that fall under “oils, animal products, and/or sauces.” Those items aren’t suitable to put in your compost bin as they attract germ-ridden pests and parasites.

Are Onions Good for Compost?

Onions can most definitely be composted, despite an online reputation for being “too acidic” for backyard compost piles. Research shows that using composted onion products can actually help control several kinds of white rot and other plant diseases. Onions compost best if they are first chopped, diced, pressed, or juiced.

  • The onion tea can then be used to make a vinegar or composted separately from the leftover onion mash (which can go into a regular compost pile).
  • If juicing onions (and making an onion vinegar type or tea) sounds too complex, just cut them up first.
  • Trust me – whole onions will degrade – but it’ll take a ridiculously long time. My test whole onion took just over a year to fall apart – while the raw, cut-up onion pieces decomposed within a few weeks.

And don’t dump a huge pile of onions into your compost all at once. If you have an unusually large stash of onions to compost, consider processing them first by chopping, dehydrating, or juicing them.

What if your compost pile is based on worms (vermicompost)? I’ve seen lots of sites and uncited literature (mostly in the form of blogs and websites) saying that vermicompost can’t handle onion waste. However, I did find a 2020 study in the International Journal of Environmental Science and Technology that showcased a successful way to vermicompost onions.

In that study, the authors detail how they could mix onions with cow dung, and it composted just fine in a vermicompost setting. In fact, it ended up being a fantastic compost mix, per the article.

Now, if you are using vermicompost and you don’t have fresh cow dung to add to the onion mix? Then you may want to chop those onions up well – and mix it in with some other elements. Or you may want to wait for further studies to be done.

What Veggies to NEVER Put In the Compost

All edible, healthy vegetables are safe to compost as long as they aren’t in sugars, oils, sauces, or animal products. So if it’s a veggie that you grow and eat, then you can compost it. Now, if it’s a vegetable that you grew and the plant (and/or the vegetable) is diseased, then you shouldn’t compost that particular specimen.

Never add any diseased plants or products to your compost pile – in order to contain that disease. We definitely don’t want to spread that plant-based disease to other parts of the garden. Or worse, spread it to other plants.

A quick note about diseased vegetables (and plants): not all commonly-called “diseases” are such, nor are they contagious. Blossom end rot, for example, isn’t a disease per se. Sure, it causes ugly-looking tomatoes, but it’s not a disease, nor is it contagious. It’s caused by symptoms of abiotic stress that lead to cell death. I know – technically tomatoes are fruits, but the principle still applies.

So if you’ve got vegetables with symptoms of abiotic stress, those are still safe to compost.

Other Ways to Deal with Leftover Cooked Vegetables

Now that we’ve talked about composting veggies, let’s talk about what to do with the vegetables that shouldn’t be put in the compost. You can do the following with any vegetables, even the ones that could be added to the compost.

  • Plan to use those vegetables in a meal later this week. Why not cook those fatback-seasoned green beans into a stew later this week? Even if they get mashed into oblivion, they could add some great background flavor.
  • Freeze-dry leftover veggies for later. Lots of vegetables are easily repurposed for later meals. So go ahead and freeze-dry them for using again later. Even if they were cooked in a sauce or some animal products, most vegetables will freeze-dry well enough for several months in storage.
  • Feed safe, leftover vegetables to your chickens. Our chickens love leftover food. And they don’t care if the veggies were cooked in some oils or sauce. They absolutely love it. An important note: make sure that you double-check each food as “safe for chickens” before you feed it to them. And please don’t feed your chickens hot vegetables.
  • Process the food to be compost-safe. This may be an option that’s too involved for many people. But if you have food that’s not safe up front for the compost bin, you may process it to a compost-friendly state. Common processing methods could include juicing, dehydrating, freeze-drying, or just removing as much of the compost-friendly components as possible.
  • Call it a “learning experience” and discard the veggie dish. Sometimes, you may cook a new dish that nobody likes. Or you may not like having that much waste. Chalk it up to a learning experience. Discard it once – and then find a better veggie dish to make in the future. Vegetables will compost – even if they’re at the dump.
  • Change how you cook in the future. So this won’t help you dispose of what you already have. But try to change how much food you cook at once to lessen leftovers and overall food waste. And change how you cook it to be safer for eating later, for feeding to your flock, or for adding to your compost bin.

Okay, so these methods will work for any leftover raw vegetables, too. But it’s nice to remember that there is more than one way to discard leftover veggies.

Personally, I still have issues cooking too many vegetables. Even though I know some of my kids have issues with vegetables (texture being the main issue), I still cook them in hopes that, one miraculous day, they’ll enjoy them more.

So I’ve learned to get creative with re-purposing leftover veggies into new meals – or just reheating them and eating them myself. My chickens also love getting the leftovers that are safe for them to eat. Sometimes, during the warm summer months, I’ll even freeze the cooked veggies as a cool treat for our hens.

Final Thoughts

Composting is an amazing way to upcycle so many things (cooked vegetables included) into a usable mulch that will continue to benefit you, your garden, and your family.

Even if you’re feeding those cooked veggies to your chickens, you’re still going to get that back as eggs, chicken manure for the compost pile, and as happy birds.

So feel free to experiment with composting cooked veggies – all while making your backyard homestead a happier, healthier place. Happy (backyard) homesteading, friends.

Related Questions

Are Bananas Good for Compost? Bananas (and their peels, once the sticker has been removed) are great for compost. They break down quickly, though, so make sure they’re taken out to the compost pile as soon as possible.

Can You Store Food in Home Depot Buckets? Orange Home Depot buckets aren’t rated as safe for food, although local Home Depot stores might sell food-grade buckets. Read my article on storing food in food-grade 5-gallon buckets (and how to know if they’re food grade) for more information.

Can You Prune Fruit Trees in the Summer or Fall? Fruit trees that need better control and shaping can be pruned in summer. Fruit trees should never be pruned in the fall, as they won’t have sufficient time to recover before going dormant. Read my article on pruning fruit trees in the summer for more details on why fall is a no-go.

Sources

  • Coventry, E, et al. “Control of Allium White Rot (Sclerotium Cepivorum) with Composted Onion Waste.” Soil Biology and Biochemistry, Pergamon, 10 Apr. 2002, www.sciencedirect.com/science/article/abs/pii/S0038071702000378.
  • Fabani, María Paula, et al. “Minimization of the Adverse Environmental Effects of Discarded Onions by Avoiding Disposal through Dehydration and Food-Use.” Journal of Environmental Management, Academic Press, 21 June 2020, www.sciencedirect.com/science/article/pii/S0301479720308768.
  • MA. Abdoli, G. Omrani, et al. “Onion Waste Recycling by Vermicomposting: Nutrients Recovery and Agronomical Assessment.” International Journal of Environmental Science and Technology, Springer Berlin Heidelberg, 1 Jan. 1970, link.springer.com/article/10.1007/s13762-020-02685-1.
  • Horiuchi, Jun-ichi, et al. Biological Approach for Effective Utilization of Worthless Onions-Vinegar Production and Composting. 4 Apr. 2003, www.sciencedirect.com/science/article/abs/pii/S0921344903000363.
  • Huang, Ju-Sheng, et al. “Empirical Model and Kinetic Behavior of Thermophilic Composting of Vegetable Waste.” Journal of Environmental Engineering, American Society of Civil Engineers, 1 Nov. 2000, ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9372(2000)126:11(1019).
  • “Increasing onion plant health by thermophilic compost.” IFOAM 2000: the world grows organic. Proceedings 13th International IFOAM Scientific Conference, Basel, Switzerland, 28 to 31, 2000, www.cabdirect.org/cabdirect/abstract/20000315028.
  • Saure, Max C. “Why Calcium Deficiency Is Not the Cause of Blossom-End Rot in Tomato and Pepper Fruit – a Reappraisal.” Scientia Horticulturae, Elsevier, 11 June 2014, www.sciencedirect.com/science/article/abs/pii/S0304423814002830.
  • “Yard and Garden.” Composting, extension.usu.edu/yardandgarden/soils/composting.

Kimberly Starr

I'm a ginger who loves being outside, homesteading, and spending time with my family. I believe humor is the best medicine, followed very closely by chocolate and tacos.

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