What can you feed the worms in your worm composter?

Composting worms aren't picky eaters: they'll eat a wide variety of biodegradable scraps. But some foods help them do their job, while others can throw the bin off balance, slow down decomposition, or cause bad smells. Here's how to feed them well.

The basic rule

Before you put anything in your worm composter, ask yourself two questions. Is it biodegradable — would it break down naturally if left outdoors? — And is it plant-based? If the answer to both is yes, your worms can most likely recycle it. The notable exceptions are citrus fruit and onions, which you should still limit. As a general rule, the more varied the menu, the healthier the ecosystem in your worm composter and the better the vermicompost you'll get.

One essential point to understand: composting worms only eat matter that has already started to decompose, never fresh, living plants. Unlike a slug, which goes straight for the leaves or fruit still growing in your vegetable garden, a composting worm needs microorganisms to start the work before it can feed. That's also why we recommend letting your scraps wilt for a few days before adding them: your worms will digest them all the better.

What worms love: nitrogen-rich scraps

No restrictions

• The vast majority of fruits and vegetables, peels included — worms love sugar; in summer, bury them under the other scraps so you don't attract too many fruit flies.
• Bruised or overripe fruits and vegetables, even rotten or moldy ones — these are even better: decomposition has already begun, which is exactly what your worms are looking for (we explain the role of molds and other helpful organisms in our guide Life inside a worm composter).
• Grains, flour (wheat, corn, rice, oats...) — sprinkle them in a thin layer rather than a thick pile to avoid any risk of fermentation and heating up; avoid nut flours (almond, hazelnut...), however, which are fattier.
• Coffee grounds, with the paper filter or pod — worms eat both the grounds and the pod; avoid aluminum pods, though, since they can't digest those ;).
• Tea bags — worms digest the bag, the string, and the tag; just remove the metal staple if there is one.
• Flower petals, wilted flowers — avoid rose canes and stems, however, which take too long to break down.

In moderation, in small amounts

These aren't the worms' favorites, but you can give them some in reasonable amounts.

• Bread, crusts, pizza crusts — in small amounts, because of the yeast: as long as it has moisture and warmth, it keeps fermenting, which can cause a small local rise in temperature and attract more fruit flies. Leftover dry bread crusts after a meal are a good way to give it to them.
• Plain rice, plain pasta (no oil or seasoning, leftovers after cooking).
• Pet hair and human hair — take a little longer to break down.

Willy's tip

Cut your scraps into small pieces: the more surface in contact with bacteria, the faster they decompose and turn into compost.

An often-forgotten point: worms have no teeth. That's why it's important to cut scraps into small pieces, about 1.6–2 in (4–5 cm), especially tougher items like melon rinds. On the other hand, some scraps, like banana peels, break down so quickly that there's no need to cut them up first. Worms partly make up for their lack of teeth thanks to crushed eggshells: once swallowed, the small fragments act like teeth in the worm's gizzard, letting it shear and grind its food from the inside.

The acidity regulator

Regulating the acidity of your worm composter once a week is one of the most important things you can do for your worms' health. Your bedding naturally tends to become acidic: some scraps, like tomatoes, ferment and acidify the bin as they decompose. Yet worms like to live at a neutral pH, between 7 and 8 — without regular regulation, it can drop as low as 4 or 5, a level worms tolerate poorly.

• Crushed eggshells — if simply crushed by hand, use the equivalent of three eggs per week in the active tray. Ground into a powder (grinder, blender, coffee grinder, or mortar and pestle), just one tablespoon a week is enough: the more finely they're ground, the faster they act on acidity, because the worms don't eat them — it's the shells that dissolve in contact with the bedding, not the other way around.
• RegulaWorm — our 100% natural lime-based blend, which works in 5 minutes. A good alternative if you're vegan or don't eat eggs: use one tablespoon per week.

Did you know?

Finding undissolved bits of eggshell in your vermicompost isn't a flaw: it's actually a good sign that the bin isn't acidic.

Carbon-rich materials: the essential moisture regulator

Along with food scraps, it's important to add carbon-rich materials regularly: they provide the carbon bacteria need to thrive, regulate moisture by absorbing some of the water released by organic scraps, and supply fiber that's useful to the worms. Aim for 50% carbon-rich material in the total amount you add, in small pieces of 1.2–1.6 in (3–4 cm).

• White paper, paper bags, kraft paper bags — if printed, choose black ink; avoid flyers, magazines, and other prints with heavy inks or plastic coatings, as well as full-page photos printed at home.
• Brown or white cardboard — egg cartons (even colored ones, which use food-grade ink), toilet paper and paper towel tubes, or lightly printed shipping boxes like the ones from Amazon: cardboard glue is plant-based and harmless to worms.
• Paper towels and tissues — as long as they aren't soiled with fats or synthetic products; even if used during a cold, they're not a problem, since passing through the worm's gut greatly reduces (by more than 90%) any bacteria they may contain.
• Straw and hay.
• Untreated wood shavings and sawdust — avoid fresh or sappy softwoods (fir, pine, cedar): their aromatic oils can irritate worms; choose a well-dried hardwood instead.
• Plant-based litter for small pets or cats — just check that it doesn't contain chemical odor absorbers.
• Dry, dead leaves.
• Coir, hemp mats — this works on the same principle as the moisture mat we describe in our guide How to start your worm composter: once it has broken down, it can be crumbled and counted as a carbon-rich addition.
• Ready-to-use carbon substrate — our premixed blend, handy if you're short on time or don't have carbon-rich material on hand.

What to avoid

Fruits and vegetables

• Fruit pits — don't break down. Seeds and small pips don't have this problem: in such rich vermicompost they sprout easily, and the worms then eat the young sprouts at the next weekly mix.
• Potato peels — their toxicity comes from solanine, a glycoalkaloid concentrated in the skin, whose level varies with the variety, exposure to light, and how far the tuber has sprouted. Test with one or two peels: if they're still intact after about ten days, your worms don't want them; if they've disappeared, you can keep giving them peels with no problem.
• Thick avocado skin and pit — break down very slowly unless finely ground.
• Onion, garlic, shallot, rhubarb leaves and stalks, squash and zucchini seeds — have deworming properties that disturb worms.
• Citrus fruit (lemon, orange, clementine, grapefruit...) — acidifies the bin.
• Pineapple — acidifies the bin as it ferments.
• Nuts (walnuts, hazelnuts, almonds, peanuts, cashews, pistachios, pecans...) as well as their shells and skins — break down very slowly unless you blend them.
• Mushrooms, leeks — best avoided, especially in the first few months, while the worm colony settles in and the good bacteria develop; they can then be reintroduced in small amounts.

Animal products

• Meat, fish, and shellfish — toxic to worms; animal proteins also produce ammonia as they decompose, which causes bad smells.
• Bones and fish bones — toxic to worms, and they don't break down.
• Dairy products — toxic to worms: their fat blocks oxygen and slows decomposition, like oils (see below), while lactose fermentation quickly acidifies the bin and can weaken the whole colony.
• Whole eggs, whites and yolks — give off bad smells as they decompose (not to be confused with crushed eggshells, which are recommended — see above).
• Animal droppings — give off bad smells and may contain dewormer residues. Some of our customers use them successfully with their composting toilets: manure worms such as Eisenia (the very species of our composting worms) digest them very well. However, we advise against it if your worm composter is kept indoors, because of the smell.

Fats

• Oil, butter, margarine, mayonnaise, fried foods, prepared foods with more than 5% fat — toxic to worms; by sticking to their skin, these products also keep air from passing through it and can suffocate them.

Other kitchen products

• Fresh spices and herbs — toxic to worms when fresh (once used in cooking or for an herbal tea, see below).
• Salty and vinegary leftovers — through osmosis, salt draws water out through the worms' permeable skin and dehydrates them (the same mechanism that kills slugs out in the open); vinegar, being very acidic, drops the pH well below the neutral level your worms need (see our acidity regulator above).

Ash, sand, and wood

• Ash, charcoal — highly alkaline and caustic, ash can literally burn the worms' sensitive skin and push the pH well above the desired neutral level, the opposite of the acidity problem (see our acidity regulator above); barbecue charcoal also often contains binders (starch, paraffin) or fire starter residues.
• Sand — does nothing for the worms and can throw the bin off balance.
• Wood (logs, raw chunks) — breaks down very slowly; not to be confused with shavings and sawdust, which are very useful as carbon-rich material (see above).

Yard and household products

• Fresh grass clippings, freshly cut grass, or green leaves, in large amounts — give off bad smells as they ferment: as mentioned above, your worms only eat matter that has already started to decompose, never fresh, living plants.
• Tobacco, cigarettes.
• Biodegradable materials or so-called compostable plastics — most of these plastics, often made from cornstarch (like PLA), need a sustained temperature of around 136°F (58°C) for several weeks to truly break down. A home worm composter never reaches those temperatures, and in the vast majority of cases neither does a regular backyard composter (it generally tops out at around 68–86°F (20–30°C)): only industrial composting facilities manage it reliably. The safest option is to put them in your food scrap collection bin if it goes to this type of facility, rather than in your worm composter or even your backyard compost.
• Plastic and non-biodegradable or synthetic products.
• Household dust — may contain residues of cleaning or synthetic products, as well as grit, dust mites, or other tiny critters that don't belong in your worm composter.
• Diseased plants — spores, bacteria, and viruses can survive vermicomposting, which doesn't get hot enough to neutralize them (unlike hot compost at over 131°F (55°C)); when you later spread your vermicompost, you could reinfect your garden.
• Used pet litter — mineral-based litters (clay, silica) don't break down; plant-based ones become a problem once soiled, because of the ammonia in urine and, for cat litter in particular, the parasite that causes toxoplasmosis, which the temperatures in a home worm composter can't neutralize. Not to be confused with clean, unused plant-based litter, which on the contrary is a good carbon-rich material (see above).
• Plant waste from outdoors — clippings, leaves, or weeds gathered in the yard: they can carry unwanted guests (slugs, insects, pest eggs), weed seeds that will sprout, or even pesticide residues if the area isn't yours; save them for a regular backyard compost pile, which is better suited to this kind of material.

Should you wait for the previous scraps to disappear?

Not necessarily: bacteria start breaking down the newest scraps while the worms feed on the older ones, and so on. It's a continuous process rather than a series of separate batches — we do, however, explain how to adjust your feeding schedule in our guide How to start your worm composter.

A few good habits when adding scraps

The most important habit: each time you feed, mix your scraps in a ratio of 50% nitrogen-rich scraps (peels, food leftovers...) to 50% carbon-rich material (cardboard, paper...). This balance is what prevents bad smells, regulates moisture, and ensures fast decomposition.

Coffee grounds are an excellent texturizing material for vermicompost: their particles literally act as a millstone in the worms' gizzard and aid digestion, while also boosting reproduction. If you grind your eggshells for your weekly acidity regulator (see above), let them dry for two or three days first: they'll crumble much more easily, and they also provide calcium, which helps with cocoon production.

To limit the acidifying effect of some scraps, let your citrus dry for a few days before adding it. Herbs like thyme, rosemary, or lavender shouldn't go into the worm composter on their own, but can be added after use — in an herbal tea or in cooking — once most of the compounds potentially harmful to worms are gone.

The right carbon/nitrogen balance and pH

Our food scraps are often too rich in nitrogen compared with carbon: that's exactly why carbon-rich additions are so important, to make up for the imbalance. If you have a way to measure acidity (a pH tester, for example), keep in mind that the mix should stay at a neutral pH, between 7 and 8 — which is the whole point of the weekly acidity regulator described above.

Adopting a weekly routine

Once a week, get into the habit of gently mixing the active tray — the top tray, just under the lid, where you add your fresh scraps: this simple step spreads the carbon-rich materials (cardboard) evenly among the nitrogen-rich materials (peels), while adding oxygen to the mix — a key factor for better decomposition. Use the same day to add your acidity regulator — crushed eggshells or RegulaWorm, with the amounts detailed above — which also limits the spread of parasites and gives the worms minerals that support their activity and reproduction.

Willy's tip

Mix the active tray and add an acidity regulator: a two-minute weekly routine that prevents most acidity problems.

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