Worms

Worms here means the composting worm itself, not the box it lives in. Fed a steady supply of kitchen and farm scraps, it eats its way through them and leaves castings - its droppings, a fine dark material used as a soil amendment. Castings hold more plant nutrient than the soil around them, may carry about 4 percent more nitrogen than ordinary compost, open up the pore spaces in soil and help it resist erosion, and can suppress some plant disease.

The animal sets the conditions, and they are narrow. Bedding is shredded paper, fallen leaves, chopped straw or coconut fibre, about 15 cm (6 in) deep, kept damp but never wet, and neither strongly acid nor strongly alkaline. Temperature matters most. The working band sits between about 15 and 25 degrees Celsius (59 to 77 F) - sources disagree on the middle but agree on the edges - and above roughly 35 degrees (95 F) the worms go dormant, while in the cold they slow and then die, since a small bed holds no warmth of its own. A household bin fed mixed scraps gets through between half the worms' own weight and their whole weight in a week; a managed open bed on a chosen feedstock eats its own weight in a day. The spread is a difference of system, not of fact: size the feeding on the slower figure and treat the faster as a ceiling.

A compost heap kills disease organisms by heating itself; a worm bed never gets that hot, so it is not the right treatment for manure or human waste. The daily mistake is feeding faster than the population keeps up: uneaten scraps sour, the bed goes airless and smelly, and flies arrive. Worms crawling out is the general alarm: something in the bed is wrong. The first castings can be taken after about four months, by pushing the worms to one side with fresh bedding and lifting the finished material from the other.