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What Composting Worms Won’t Eat: A Comprehensive List


Food items that red wiggler worms shouldn't eat.

Okay, so I keep running across these lists of all of the food items that red wigglers will eat. But what I’ve really been needing to know is what are the items I need to avoid. Sure, I know the obvious ones like meat and dairy, but is that it? I decided to go on a quest and compile the most comprehensive list that I could of food items they will not (or should not) eat. After all, composting worms are well-known for eating a wide variety of different foods, even some that people wouldn’t traditionally consider edible. But that doesn’t mean that they should eat just anything.

So, what will red wigglers not (or should not) eat? Composting worms shouldn’t eat the following:

  • Citrus
  • Meats
  • Oily or processed foods
  • Dairy products
  • Allium plants like onions or garlic
  • Spicy foods
  • Rotten food
  • Animal feces*
  • Foods that are acidic

Giving composting worms access to a balanced diet they can safely eat is one of the major factors in having a thriving worm bin. I’ve made my share of mistakes and there is no reason for you to repeat them. Keep reading to learn more about worm composting and how to avoid giving your worms foods they won’t eat.

Composting Worms Won’t Eat Citrus

Composting worms won't eat citrus and it can effect the pH of the bedding.

Citrus fruits and citrus fruit peels and rinds are not a good choice for feeding composting worms. The reason is that the fruit of citrus trees is highly acidic, and this acid is irritating to worms as it breaks down in the soil.

Citrus rinds have strong aromatic oils that worms don’t like (they breathe through the surface of their skin), and even when they are broken up into very small pieces, they still take forever to decompose. I hear people say that you can feed them in very small quantities but it’s not worth the hassle. Just avoid them.

Examples of citrus fruits and citrus peels that should be avoided include the following:

  • Oranges
  • Tangerines
  • Lemons
  • Limes
  • Grapefruit
  • Kumquats
  • Yuzu
  • Buddha’s Hand
  • Citron

Since they do not decompose easily and worms won’t readily eat them, these peels are better suited for other practical purposes around the home and garden.

Another reason to avoid citrus is that rather than soften and liquify, citrus peel tends to mold instead. This introduces a quick-spreading mold to the soil of the composting bin and can potentially damage the delicate balance within the bin. More on moldy foods later.

Learn all about vermicomposting. Read Worms at Work: Harnessing the Awesome Power of Worms with Vermiculture and Vermicomposting (link to Amazon)

Composting Worms Shouldn’t Eat Meat

A major food group that should be avoided in the compost bin, whether you have composting worms or not, is meat. This is not just because worms don’t like it and won’t eat it, but also because rotting meat in the compost bin smells repulsive and tends to attract unwanted pests like flies and rats.

Since nobody wants to open their worm bin and find it full of maggots instead of red wrigglers, the best option is to not put any kind of meat or animal products in a worm bin. Just don’t.

A problem with meat as it pertains to the diet of a composting worm is that meat is very high in protein, and high levels of protein are poisonous to composting worms. So not only do you end up with a compost bin that stinks to high heaven, but you’ll also end up with a bunch of sick and dying worms. Learn more about worms dying due to protein poisoning and other common causes from the following article:

Avoid Oily Foods

Composting worms can’t properly break down and process oils or other kinds of fat. And when introduced to the environment of a worm bin, oils and fats go rancid. This can again lead to very off-putting smells that inevitably attract pests. Because worms won’t eat oily foods, they’ll just sit in the bin and rot.

Like meat and other high-fat foods, anything that has oil in it should be kept far away from the worm bin or any other compost.

They Shouldn’t Eat Processed Foods

Processed food can be harmful to red wigglers.

Processed foods should generally be kept far away from your worm bin. A practical reason is that many processed foods are chock full of preservatives, which significantly increase the amount of time it takes for the food to naturally decompose. Think of it as an embalming fluid, but for your snacks.

Not only are these preservative chemicals potentially dangerous to composting worms, but your red wigglers will generally avoid them. You can expect any processed food to be left in the bin to rot rather than being eaten up by your worms.

Here are some of the processed foods you should keep out of your worm bin:

  • Cake
  • Baked goods
  • Cooked foods that have had butter or other fats added for flavoring

Most people invest in a worm bin as part of a gardening adventure or in an effort to eat and consume more thoughtfully, so if you’re bummed out about the prospect of not being able to compost your processed foods, think of it as an excuse to buy whole organic foods instead. It’s for the worms!

In the end, there’s a serious component of common sense at play here. Remember that we need to feed them organic matter. Food items that are heavy with preservatives are not the way to create healthy, happy worms.

Red Wigglers Won’t Eat Dairy Products

Dairy products such as cheese are a trifecta of dealbreakers for your worm bin—they’re high in fat, they’re high in protein, and worms don’t care to eat them. That means that putting any kind of dairy product in your worm bin is only going to leave you with a worm bin that smells like rotting milk (and possibly some sick worms).

The pungent smell that dairy products give off is bound to attract pests, and once those fats start rotting in the bin, you’re not even going to want to open it.

Like meat and oils, dairy products should be kept completely away from your composting worms.

Here is a list of dairy products you should avoid adding to your composting worms as a food source:

  • Cheese
  • Milk
  • Butter
  • Food items that are cooked with or contain any of the above

Composting Worms Shouldn’t Eat Alliums like Garlic and Onion

Actually, it’s not like they can’t eat alliums, it’s more like they shouldn’t—as they break down, alliums release noxious chemicals into the soil that the plants use as a natural defense. This is the same chemical that makes garlic smell pungent, and why onions cause you to cry.

A worm bin may process alliums once they’re decomposed enough, but the substances they release into the soil can be irritating to composting worms since they breathe through their skin. Imagine having to breathe a vapor of the same substance that causes you to tear up whenever you chop an onion, and that’s a pretty good idea of how alliums are irritating to composting worms.

An additional drawback to alliums in the composting bin is that they tend to stink a lot more as they break down compared to other fruits and vegetables.

Your Worms Can Eat Bread, But Probably Shouldn’t Unless You Prepare It

Like citrus rinds, bread tends to mold quickly when introduced to a compost bin, and this can lead to the introduction of mold that may or may not damage the ecosystem of the compost bin and the worms living inside it.

If bread is fed to your composting worms, your best bet is to break the bread up very finely, bury it beneath the top layer of soil in the compost bin, and add moisture. This will help the bread become mushy and break down into the soil before it has a chance to grow airborne mold.

And don’t give them too much of it at one time. Small feedings will help to prevent it from molding.

They Won’t Eat Large Pieces of Food

Ever seen a worm’s mouth? My point exactly. Composting worms can only eat and absorb food that is in a very small, very soft state, which means that you can’t just throw large dry leaves of old cabbage or some other starchy food into the compost bin and expect the worms to be able to process it quickly or efficiently.

If you place food in the compost bin in pieces that are too big, it will often begin to rot before the worms have a chance to eat it.

This means that regardless of what kind of organic fruits and vegetables and grains you put in your worm bin, they need to be broken down into small pieces. Otherwise, it’s going to take forever and a day for your compost bin to process correctly.

Now, in all fairness, if you drop a large vegetable into your bin, it will slowly decompose and as it does, the worms will feed on the parts that are breaking down. Just to illustrate this, here is a short timelapse video of a pumpkin being consumed by red wigglers. But what you need to realize is that they aren’t actively eating up the whole pumpkin. They are nibbling away at the bottom as it decays. Still, it’s fascinating to watch and is less than two minutes long.

Pumpkin vs Red Wigglers 62-day time-lapse - FAST PLAYBACK - worm vermicomposting

Composting Worms Shouldn’t Eat Spicy Foods

I know what you’re probably thinking—it’s the end of the summer, you’ve finished harvesting the garden, and you’re left with three plastic zippered bags full of neglected, leftover cayenne peppers from the garden that are too old to freeze or dry and too mushy to eat. What do you do with them? Throw them in the worm bin?

The answer to that is a resounding “no”. And the reason is one word: capsaicin. This irritating chemical compound is what makes spicy foods “hot” on our tongues, and the reason that these are a poor choice for a worm bin is that this chemical leeches into the soil surrounding a pepper as it decomposes.

As they wriggle through the soil, composting worms inevitably come into contact with this contaminated soil, and the capsaicin can make them sick or even kill them. You have to think of the compost bedding as the composting worms’ home and rotting peppers as throwing a few cans of pepper spray into somebody’s home.

Don’t pepper spray the worms!

Spicy foods like peppers are also typically high in acid, and since the pH of a worm bin’s soil should be as close to neutral as possible, you don’t want to introduce any elements that can potentially cause a pH problem in your compost. 

Will Red Wigglers Eat Rotting Food?

We’ve all done it at one point or another. You leave a Tupperware full of salad in the back of the fridge by accident until it’s growing a new life form, or one of the potatoes in your brand-new sack is mushy and leaking something that smells vile. This food is definitely rotten—can you put it in your worm bin?

If the food has already begun to rot in the open air without soil exposure, it’s probably not a great idea to throw it in the worm bin even if it’s organic. This is because rotting food will not only make your worm bin smell bad to you and attractive to pests and rodents, it can potentially introduce disease into the bin as well.

Another problem with putting rotting food in the compost is that a lot of the time, the rotting food in our fridges is cooked food that has had some kind of dairy, meat, or oil product added to it. As soon as you add high levels of fat or protein to a food, it is not suitable for a  worm or compost bin. (Not unless you’re trying to start a maggot farm instead.) To get a better understanding of where to draw the line, read my article Can Red Wigglers Eat Mold and Rotten Food?

Will Compost Worms Eat Manure and Feces?

Composting worms thrive in well-aged manure, but you should never put fresh manure from horses, cows, or other livestock directly into a worm composting bin. This is because fresh manure is very high in nitrogen, which can actually have a detrimental effect on your composting worms.

This short YouTube video outlines the cautions to take when feeding your worms cow manure.

Can I Feed My Compost Worms Cow Manure?

While we’re on the subject of animal droppings, dog and cat feces from your household pets are also not a good option for a worm bin. Cat waste is usually collected in cat litter, which is not edible to worms and can actually cause them to develop digestive blockages that rupture and kill them.

Dog feces can technically be used for composting as long as it isn’t added in large quantities all at once, but because of the risk of introducing pathogens to the soil, it is usually a better option to keep all forms of poop out of your composting bin.

Human feces should likewise not be fed to composting worms. Not only is there the same pathogen risk that there is with adding dog feces to a worm bin, but there is also the introduced factor of potential biohazards involved. Homemade composting systems that involve human waste are usually against sanitary code as well, so it’s just better avoided.

Will Red Wigglers Eat Paper?

Great news for homesteads and gardeners going paperless—composting worms will happily eat paper, provided it is shredded into small enough pieces that it can be absorbed into the soil easily. (If you want more info, I have a whole article on this titled Do Red Wigglers Eat Cardboard, Cartons and Other Papers?)

In fact, paper makes a great foundational element for worm bin bedding, as it can be used to retain moisture in the bin and slow decomposition. Paper acts as good bedding for the worms until it finally breaks down, at which point it becomes viable food.

One kind of paper that shouldn’t be added to worm bins is paper that is glossy such as magazine pages. That is because this type of paper has been chemically treated with plastic in order to make it appear shiny, which makes it very difficult to break down in a worm bin. Even if it does manage to break down a little, the plastic coating on this type of paper renders it inedible for the worms.

Will Composting Worms Eat Sawdust?

Sawdust is a great component to add to the bedding of your worm bin as a potential food source with one major caveat—sawdust from pressure-treated lumber should not be used. The various chemicals used to pressure-treat lumber (such as arsenic) are poisonous to composting worms.

Instead, if you want to feed your worms sawdust, use fallen limbs or other organic pieces of scrap wood from around your property and run them through a wood-chipper until they create coarse sawdust. This sawdust can then be used to sprinkle into your worm bin to help control excess moisture and smells coming from the compost. Sawdust from a workshop would be fine too so long as you are working with raw woods, not treated.

Will Composting Worms Eat Grass and Weeds?

Take caution when feeding your compost worms weeds from your lawn or garden. Those seeds can survive the composting and end up back where they started.

While you might be tempted to throw pulled weeds in your bin (and worms would happily eat them), you might want to think twice about it if you use soil from that same composting bin to spread on your garden. Weed seeds can lie dormant in the soil until they are spread in the field, and this can potentially lead to trouble with weeds.

Lawn clippings can only be used in a worm bin if the grass that they’re cut from has not been treated with fertilizers or pesticides, as these chemicals can be dangerous to composting worms. By the way, worm castings are a great natural lawn fertilizer!

As long as you don’t introduce unwanted weeds or pesticides to the worm bin, lawn clippings can be a good dry addition to help balance out excess moisture, and a cut of fresh mowed grass can also help improve the worm bin’s smell when it starts to get a little ripe. But I would add it in moderation. Remember when we discussed fresh manure and the caution of nitrogen? That applies to fresh grass clippings too. A little is fine – too much is not.

One of the benefits of using fresh-cut lawn clipping is that they are still usually pretty wet when they’re first cut and get powdery when they are given a chance to dry out, so they can be used to either add moisture to the worm bin or detract moisture, depending on which capability you need at the time. 

Conclusion

Two of the biggest problems with adding things to the compost bin that composting worms won’t eat is that it causes rotting problems in the worm bin or introduces some kind of foreign substance that is toxic to the worms themselves.

As long as you keep your composting worms in plenty of fresh organic scraps that they like, they’ll continue to produce plenty of fresh compost for you just as long as you want to keep feeding them.

Looking for the right worm bin for your needs? I’ve outlined the benefits of features of what I believe to be the best worm bins, including best for an apartment, best for kids, and best overall.

Paul Brown

Paul has a two-acre yard on red clay soil in Southeast Texas. He knows exactly what the challenges are to nurturing a thriving yard in difficult soil. He takes a practical approach to yard improvement and enjoys putting best practices and “golden rules of lawn care” to the test. Click here for Paul’s author page

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