Worm Bin Sizer

The worm you want is Eisenia fetida, sold as red wigglers or red worms. They are surface feeders that evolved to live in decomposing organic matter, which is exactly what a worm bin is. The earthworms you dig up in the garden, Lumbricus terrestris, are soil dwellers that tunnel deep into mineral earth. They do not thrive in a bin and will not process food scraps efficiently.

Most garden centers do not stock red wigglers. Order from a reputable supplier online. One pound of worms is a reasonable starting quantity for most households. The population will double every 60 to 90 days in good conditions, so the bin will catch up to your scraps volume even if you start a little short.

Red wigglers work best between 55 and 77 degrees Fahrenheit. Below 50, activity drops off sharply. Above 85, the worms will try to leave the bin. Sustained heat above 90 can kill them outright. This matters more than most new worm keepers expect.

A basement, laundry room, or climate-controlled garage is ideal. A bin left in a hot shed or outbuilding in midsummer is a risk. In winter, an unheated garage in a cold climate will go dormant at best. The bin does not smell if it is managed correctly, which makes indoor keeping more feasible than people assume. A well-run bin smells like soil, not garbage.

Start with shredded newspaper, cardboard, or coconut coir. Avoid glossy paper. The bedding should be moist before the worms go in. Same wrung-out sponge rule as a compost pile. Worms live in and on the bedding and use it as a carbon source. Add more as the pile compacts and gets wet.

A layer of damp cardboard or burlap over the surface keeps moisture in and light out. Worms avoid light and will stay near the surface as long as it is dark and damp. If you open the bin and they immediately retreat downward, the surface is probably too dry or too bright.

Crushed eggshells are worth adding at every feeding. Worms use the grit for digestion and the calcium helps keep the bin pH from going acidic. Rinse the shells, dry them, and crush them before adding.

Fruit and vegetable scraps are the foundation. Coffee grounds and unbleached filters compost quickly and the worms move toward them. Tea bags work if you remove any staples. Shredded cardboard and paper round out the carbon side.

Go easy on citrus. A peel here and there is not a problem, but a heavy load of orange rinds pushes the bin acidic faster than the worms can buffer it. Same with onions and garlic. Worms will eventually process them, but a bin loaded with alliums is not a happy bin.

Skip meat, fish, dairy, and anything oily or greasy. In a closed bin these create odor problems quickly and attract pests. Salty foods (chips, pickles, anything heavily salted) are toxic to worms at the concentrations that form when salt concentrates in the bin. Bread and grains are tolerable in small amounts but tend to attract fruit flies, so bury them well.

Fruit flies are the most common complaint and almost always come from food scraps left exposed on the surface. The fix is to bury food under the bedding rather than laying it on top. A layer of damp cardboard over the surface helps further. Apple cider vinegar in a jar with a paper funnel works as a trap for the adults. The population will come down within a week or two once you stop surface-feeding.

If the bin smells like rot or ammonia, it is either too wet, too acidic, or overloaded with nitrogen-rich material. Add dry bedding, reduce feeding for a week, and turn the material gently to introduce air. A healthy bin smells like soil. Any other smell is information about what to adjust.

If worms are escaping, something in the bin is driving them out. Check temperature first. A warm bin in a warm room will send them looking for cooler ground. Also check moisture and pH. A bin that goes acidic from citrus or protein overload will cause mass migration. Adding crushed eggshells and dry bedding usually resolves it within a few days.

Every three to six months, depending on how actively you feed. The easiest method: push all the material to one side of the bin and add fresh bedding and food only to the other side. Over two to three weeks, most of the worms will migrate toward the food. Scoop out the worm-free side. Finished castings look like dark crumbly soil and smell like earth. If you can still identify what went in, leave it longer.

Castings will not burn plants even at high application rates, which makes them more forgiving than most amendments. A tablespoon per transplant hole, a thin top-dress on established beds, or brewed into compost tea. A six-month yield from a well-managed 4-square-foot bin is roughly a five-gallon bucket of castings, worth significantly more by weight than the scraps that went in.