Vermicomposting, or worm farming, is a natural process where specialized earthworms, like the Red Wiggler (Eisenia fetida), convert organic waste into a nutrient-rich soil amendment called vermicast, or worm castings. Understanding what to feed them is the foundation of a successful system. The worms primarily feed on the microorganisms and fungi that first break down the organic matter, making food preparation as important as the food itself.
Acceptable Food Sources
Composting worms thrive on a diet derived mostly from plant matter, often referred to as “greens.” Raw fruit and vegetable scraps, such as peels and cores, form the bulk of their intake. These materials are consumed after microbes have begun the initial decomposition process, making the nutrients accessible.
The worm bin also requires “browns,” or carbon-rich materials, which serve as bedding and a supplementary food source. Shredded, plain cardboard, brown paper bags, and newspaper are ideal, but avoid paper with glossy finishes or heavy color inks. These carbon sources help balance the high moisture content introduced by food scraps, maintaining an aerobic environment.
Specific additions include spent coffee grounds and used tea bags, which provide nitrogen and beneficial texture. Rinse coffee grounds slightly to prevent excessive acidity. Plain starches like cereal, bread, and pasta can be included in small quantities, provided they are completely plain. Ground-up eggshells should also be added occasionally, as the fine particles act as grit in the worm’s gizzard, aiding in physical breakdown.
Foods to Avoid
Certain common kitchen scraps should be excluded entirely as they destabilize the worm bin ecosystem. Meat, poultry, fish, and all dairy products are unsuitable because they break down slowly and attract pests like rodents and flies. As these animal products decompose, they become rancid and create foul odors that signal the presence of harmful anaerobic bacteria.
Any food item containing excessive oil, grease, or fat must be avoided, as these substances can coat the worms’ skin, interfering with their ability to breathe. Highly acidic foods, such as citrus peels and pineapple, should not be fed in large amounts. A large influx of these materials can lower the bin’s pH, creating an unhealthy environment for the worms, which prefer a neutral pH balance.
Salty or heavily processed foods are also detrimental, as high salt concentrations can cause worms to dehydrate and disrupt their digestive systems. Additionally, dog and cat feces should never be added to a home vermicomposting system because they may contain pathogens and parasites that the bin’s low temperature cannot eliminate.
Managing the Feeding Process
Food Preparation
Preparing the food before adding it to the bin significantly speeds up the decomposition process. Chopping or blending scraps into smaller pieces, ideally less than one inch, increases the surface area for microbes to colonize. Some keepers freeze and thaw food waste, which helps rupture the cell walls of the scraps and makes them easier for the worms to digest.
Feeding Rate and Frequency
Frequency and amount are determined by the worm population’s consumption rate, not a fixed schedule. A general guideline is to feed the worms only what they can consume in two to three days. Beginners should start by feeding a small amount, perhaps one-quarter to one-half pound of food per pound of worms, and then observe how quickly it disappears. The best approach is to practice the “wait and see” method: only add more food once the previous meal has been mostly processed.
Placement and Troubleshooting
Food should always be buried just beneath the bedding in a different spot each time. This technique helps prevent fruit flies and ensures all worms have access to the meal. If an uneaten meal is still present after a week, it indicates overfeeding. This must be corrected by stopping feeding immediately until the worms catch up.