Using earthworms to process organic waste is a highly effective method known as vermicomposting. This technique harnesses the natural digestive power of specific worm species to convert kitchen scraps and other organic materials into a nutrient-rich soil amendment called vermicompost, or worm castings. The resulting product is prized by gardeners for its high concentration of beneficial microbes and plant nutrients. Successful vermicomposting relies on selecting the right worm species and maintaining a carefully controlled environment, which allows the worms to thrive and continuously turn waste into a valuable resource.
The Right Worms for the Job
Not all earthworms are suited for the confined, high-density environment of a composting bin. Common garden earthworms, classified as anecic or endogeic species, tend to burrow deep into the soil and do not efficiently process surface-level organic waste. These deep-dwelling worms are accustomed to lower population densities and would quickly migrate away from the concentrated food source in a typical composting system.
The worms required for vermicomposting belong to the epigeic category, meaning they are surface dwellers that naturally live in decaying organic matter like leaf litter or manure. The two most popular species are the Red Wiggler (Eisenia fetida) and, to a lesser extent, the European Nightcrawler (Eisenia hortensis). Red Wigglers are considered the composting champions because they reproduce rapidly and tolerate the dense populations found in a worm bin.
Red Wigglers thrive in the top few inches of their environment. While European Nightcrawlers are larger and can tolerate a broader temperature range, Red Wigglers are more prolific breeders and generally more efficient at quickly breaking down kitchen scraps. The efficiency of these epigeic species makes vermicomposting a practical way to manage household food waste.
Setting Up the Composting System
A simple opaque container, such as a plastic storage bin or a purpose-built system, works well, provided it includes adequate drainage and ventilation. Proper air holes should be drilled on the sides and bottom to ensure the worms have access to oxygen and to prevent harmful anaerobic conditions.
The initial layer, known as bedding, must be a moist, carbon-rich material that provides shelter and retains moisture, such as shredded newspaper, cardboard, or coconut coir. This bedding should be soaked and wrung out until it has the consistency of a damp sponge (60 to 80 percent moisture). This damp environment is necessary because worms breathe through their skin and require consistent moisture to survive.
Controlling the temperature is important, as composting worms are sensitive to extremes. Red Wigglers prefer a temperature range of 55°F to 77°F (13°C to 25°C); activity decreases significantly outside this window. Temperatures above 85°F (30°C) can cause stress or death, while freezing temperatures cause the worms to become inactive. Placing the bin indoors or in a sheltered area helps regulate these conditions, protecting the colony from direct sunlight and frost.
Managing the Worm Diet and Feedstocks
Worms feed on the microorganisms that break down the organic matter. Suitable feedstocks should include soft fruit and vegetable scraps, crushed eggshells for grit, coffee grounds, and tea bags. Chopping food into small pieces, ideally less than one inch, increases the surface area for microbes and accelerates the decomposition process.
Certain materials must be avoided because they can harm the worms or disrupt the bin’s delicate balance. Meat, dairy products, and oily foods should not be added, as they take a long time to break down, can attract pests like rodents, and may create foul odors. Highly acidic items, particularly citrus peels, can lower the bin’s pH to a level toxic to the worms, which thrive best in a near-neutral pH range of 6 to 7.
The proper feeding technique involves burying the food scraps beneath the bedding, which helps to minimize odors and prevent pest attraction. It is important to feed the worms only what they can consume in about a week, rather than overloading the bin. Overfeeding can lead to the accumulation of decaying material, which can cause the bin to become overly wet and anaerobic, potentially suffocating the worms.
Harvesting the Finished Product
After several months of operation, the original bedding and food scraps will have been converted into a dark, crumbly material known as worm castings. These castings are the finished product and should have an earthy, pleasant smell. A high concentration of castings can eventually become an unhealthy environment for the worm colony, making harvesting necessary.
A popular method to separate the worms from the castings utilizes the worms’ natural aversion to light, a trait known as photophobia. The contents of the bin are gently piled into cone-shaped mounds under a bright light source, which causes the worms to burrow down to the bottom of the piles for shelter. The worm-free top layers of the castings can then be scraped away every few minutes until only a dense cluster of worms remains at the base of the cone.
Another common technique involves a migration system, where new food and bedding are added only to one side of the bin. The hungry worms will gradually move to the fresh food source, leaving the finished castings on the opposite side to be easily scooped out. The harvested castings can be used as a potent soil amendment or brewed into a liquid fertilizer known as compost tea.