Indoor composting is an effective way to recycle kitchen scraps and produce a nutrient-rich soil amendment, known as compost, without needing a backyard. This process involves the managed decomposition of organic materials by microorganisms under controlled conditions. Vermicomposting—composting with worms—is the most common and accessible method for DIY indoor setups. This method relies on red wiggler worms (Eisenia fetida), which consume bedding and food scraps, converting them into valuable worm castings. Properly managed, a vermicomposting bin should be odorless and highly efficient at diverting food waste from landfills.
Selecting the Indoor Composting Method and Materials
Choosing the right components ensures the system can support a thriving worm population. Vermicomposting is preferred over methods like Bokashi fermentation because it produces immediate, usable soil conditioner, rather than an acidic pre-compost material. Opaque plastic storage bins, typically between 8 and 18 gallons, work well for a DIY bin, as worms prefer a dark environment. The bin should be 12 to 18 inches deep to allow sufficient space for the worms to move and for the bedding layers to function.
A drill with a small bit (1/8-inch or 1/4-inch) is needed to create holes for airflow and drainage. Initial bedding materials must be carbon-rich and chemical-free, such as shredded black and white newspaper, corrugated cardboard, or coco coir. This bedding provides a habitat and a secondary food source. The composting organisms must be red wiggler worms (Eisenia fetida), as common garden earthworms do not thrive in this high-organic environment. A good starting population is about one pound of worms for every pound of food waste intended to be processed weekly.
Physical Construction of the Vermicomposting Bin
The construction focuses on creating a safe, aerated, and well-drained habitat. Using a plastic storage container, the first step is to create ventilation holes in the lid and along the top perimeter of the bin sides. Drilling multiple small holes (1/8-inch in diameter) every few inches ensures adequate oxygen exchange for the aerobic decomposition process. This oxygen is necessary for the worms and the beneficial microorganisms that break down the waste.
For drainage, a single-bin design requires drilling several holes in the bottom to allow excess liquid, or leachate, to escape. In a two-bin stacked system, the upper working bin needs holes in its bottom and rests inside a second, intact bin that serves as a collection tray. This design prevents the bedding from becoming waterlogged, which can lead to anaerobic conditions harmful to the worms. The lid must fit securely to manage moisture and prevent pests or escaping worms.
Preparing the initial bedding involves shredding the material into narrow strips and thoroughly moistening it. The bedding should be soaked and squeezed until it feels like a wrung-out sponge—damp but not dripping. This moist material is layered into the bin to a depth of 6 to 8 inches, filling the container approximately two-thirds full. Adding a handful of soil or crushed eggshells introduces beneficial microorganisms and provides “grit,” which aids the worms’ digestive process.
Operational Management and Troubleshooting for Success
Once the bin is constructed and the bedding prepared, the worms are introduced gently onto the surface. Give the worms time to acclimate to their new environment, typically a few days, before beginning the first feeding. A healthy worm population can consume roughly one-third to one-half of their body weight in food scraps daily once established.
Worms thrive on a diet of:
- Fruit and vegetable scraps.
- Coffee grounds.
- Tea bags.
- Crushed eggshells.
These items should be cut into small pieces before feeding, as worms lack teeth and rely on microbes to soften the food. Avoid adding meat, dairy products, oils, or salty foods, as these quickly putrefy, create strong odors, and attract pests. Food should always be buried 3 to 4 inches beneath the bedding in different areas of the bin to prevent fruit flies from laying eggs on exposed waste.
Maintaining the correct moisture level is paramount; the bedding should feel like a damp sponge. If the material is too dry, the worms will not thrive, but if it is too wet, oxygen flow is restricted, creating anaerobic pockets that can cause the worms to escape. Aeration is achieved by gently turning the top layer of bedding every few weeks to prevent compaction and introduce oxygen. A foul odor, often described as sour, signals overfeeding or excessive moisture.
If an odor is present, it indicates the food is rotting faster than the worms can process it, leading to an anaerobic environment. The solution involves removing any uneaten, decomposing food and adding new, dry carbon-rich bedding to absorb excess moisture. Fruit flies can be managed by ensuring all food scraps are covered with bedding and by reducing the moisture level, as they prefer wetter conditions to reproduce. A sudden exodus of worms suggests a fundamental problem, such as high moisture or an overly acidic environment, which can be corrected by adding crushed eggshells.