Worms have their likes and dislikes, but luckily for any would-be worm farmer, they are not as picky as kids (or some adults). Worms are vegetarian and the bins need a carbon-and-nitrogen mix, just like a normal compost system.
Worms like neutral or basic pH foods that are moist, soft, and bite sized. They like a mix of “green” nitrogen-rich foods and “brown” carbon-rich ones at about a one-to-one ratio. The browns help absorb the odors and help keep the bin environment healthy, while the greens are largely food for worms. One rule of thumb is that if it stinks after sitting for a few days, it’s likely a green, if not, it’s a brown.
- Melon and squash rinds
- Fruit and vegetable peelings and skins (see “Don’t Feeds” below for exceptions)
- Leafy greens
- Breads and pastas
- Coffee grounds and tea leaves (and bags)
- Shredded, wetted paper and cardboard (newsprint, nonbleached office paper, NOT glossy or magazine — when in doubt, just recycle it)
- Eggshells (crushed and ground is best)
- Egg cartons
- Dry leaves
Worms do not like acidic foods, nor those that are too hard, dry, large, or toxic. This category has two divisions. Some foods shouldn’t be fed because they’ll create an unwanted situation (e.g., smell, growth, or pest attraction). Others should be avoided because they’re toxic. A few of these modify the “Do-Feeds,” such as citrus peels, which are fruit peelings but are too acidic.
- Citrus and pineapple peels (too acidic, but will eventually break down and be eaten)
- Garlic and onion peels (too smelly, but will be eaten eventually)
- Tomato, potato, or other sprouting foods (which will be eaten, but you have to kill the sprouts; also be careful of putting too much tomato waste, which is moderately acidic)
- Processed foods with lots of preservatives and chemicals (these are made to inhibit the breakdown we rely on in composting)
- Salt and oil, such as salad dressing
- Meat and dairy foods (they become rancid, smell, and attract insect and mammal pests)
- Large amounts of vegetable matter (like grass clippings) that would raise the temperature of the bin
- Avacado and other large fruit pits
- Yard or garden waste treated with pesticides, chemicals, or nonorganic fertilizers.
- Animal feces
- Paper whitened with bleach or made colorful and glossy.
- Sawdust from treated lumber
When in doubt, don’t feed it to the worms unless you would eat it or it a “brown” described above (which most people don’t eat, but I won’t judge if you do).
Just like us, worms like food prepared to be more easily ingested. The best thing to do is to blend up the food scraps before adding it to the bin. Allowing nitrogen-rich foods to break down for a few days in a tightly lidded compost pail is thought to jump start the compost process, too.
If flies or other pests are becoming an issue, the compost can be frozen and then thawed before putting in the bin. Others microwave the compost (the term “hot garbage” comes to mind) to kill of organisms.
Adding Foods to the Bin
Simply dumping fresh scraps on top of the surface will work, but this is not the best practice as it will attract flies and let off more smell than you would like. One popular method is to spread out the scraps and then put a few layers of wet newspaper on top to keep off the flies and make a dark and inviting environment for the worms to come up into. My preference is to carefully dig a trench and deposit the fresh scraps, which are then covered with worm castings. The next feeding is deposited in a parallel trench, and so on across the substrate.
Worms can eat half their body weight each day, so a pound of worms (ca. 1000) can take about 3.5 lb each week. It is better to underfeed worms than overfeed them, and small additions over the week are better than saving everything up for a fortnightly addition.
This is one article in a series of posts about vermicompost, or using worms in compost systems. Follow this link to see all posts in this series.
Check out these other resources:
Gardening Know How
University of California–Santa Barbara
Uncle Jim’s Worm Farm