Ever since plant pathologist Robert D. Raabe introduced the Berkeley Composting Method, gardeners have been turning their piles frequently to facilitate rapid rotting. Compost tumblers reduce the labor of turning a pile, forkful by forkful, but they cost in the hundreds of dollars, which is a bit pricey for a process that's ordinarily free. However, a backyard tinkerer with modest skills can make his own with inexpensive, often reused materials, in a weekend.
By far the simplest design for a compost tumbler is a single container than rolls freely on the ground to mix its contents. To make one, find a food-grade barrel of at least 55 gallons capacity and a tight-fitting lid. The size of the drum determines how much material you can compost at once; larger sizes also facilitate rapid and sustained heat in the barrel. Make air holes to allow airflow and excess moisture to drain. Don't skip the air hole-making step, as anaerobic composting produces methane, which would be a fire and explosion hazard if trapped in a tightly sealed container. A few 6-inch (10cm) holes covered with wire mesh to hold in contents will achieve sufficient airflow, as will 1/2-inch (0.8cm) holes drilled every 6 inches all over the barrel. With these easy steps, this compost tumbler is complete. To use, fill with a mixture of green and brown vegetative waste, wet it well and seal. Every day or so, roll the tumbler to redistribute the contents. In a few weeks, assuming the mixture doesn't get too dry, the compost will be ready to use. The Shopping Matchmaker website shares a straightforward plan for a rolling compost tumbler (see Resources).
Slightly more complex than the rolling tumbler, but also more convenient to use, is the turning tumbler. The basic design of the drum, complete with air holes, is the same, but this time, the barrel is mounted on one axis to a frame that allows it to turn in place. The September 2008 issue of "Boy's Life Magazine" includes clear instructions for constructing a turning compost tumbler (see Resources).
Auger Compost Mixer
Technically, auger compost mixers are not tumblers, since they remain stationary while an auger mixes the contents by turning through the center of the composting material. The auger may prove difficult to turn if the compost is heavy, but it will do some of the job of shredding the materials. The Earth Tub is a commercial composter by Green Mountain Technologies that works on this principle (see Resources). Not many home gardeners build auger tumblers, though some do push post hole digger augers into their piles to mix them.