The compost tumbler is a clever method that accelerates decomposition by improving aeration and facilitating frequent turning. A rotating drum holding from eight to eighteen bushels (the larger sizes look like a squat, fat, oversized oil drum) is suspended above the ground, top-loaded with organic matter, and then tumbled every few days for a few weeks until the materials have decomposed. Then the door is opened and finished compost falls out the bottom.
Tumblers have real advantages. Frequent turning greatly increases air supply and accelerates the process. Most tumblers retard moisture loss too because they are made of solid material, either heavy plastic or steel with small air vents. Being suspended above ground makes them immune to vermin and frequent turning makes it impossible for flies to breed.
Tumblers have disadvantages that may not become apparent until a person has used one for awhile. First, although greatly accelerated, composting in them is not instantaneous. Passive bins are continuous processors while (with the exception of one unique design) tumblers are "batch" processors, meaning that they are first loaded and then the entire load is decomposed to finished compost. What does a person do with newly acquired kitchen garbage and other waste during the two to six weeks that they are tumbling a batch? One handy solution is to buy two tumblers and be filling one while the other is working, but tumblers aren't cheap! The more substantial ones cost $250 to $400 plus freight.
There are other less obvious tumbler disadvantages that may negate any work avoided, time saved, or sweaty turning with a manure fork eliminated. Being top-loaded means lifting compost materials and dropping them into a small opening that may be shoulder height or more. These materials may include a sloppy bucket of kitchen garbage. Then, a tumbler must be tumbled for a few minutes every two or three days. Cranking the lever or grunting with the barrel may seem like fun at first but it can get old fast. Decomposition in an untumbled tumbler slows down to a crawl.
Both the passive compost bin and the highly active compost tumbler work much better when loaded with small-sized particles. The purchase of either one tends to impel the gardener to also buy something to cut and/or grind compost materials.
The U.C. Method--Grinder/Shredders
During the 1950s, mainstream interest in municipal composting developed in America for the first time. Various industrial processes already existed in Europe; most of these were patented variations on large and expensive composting tumblers. Researchers at the University of California set out to see if simpler methods could be developed to handle urban organic wastes without investing in so much heavy machinery. Their best system, named the U. C. Fast Compost Method, rapidly made compost in about two weeks.
No claim was ever made that U. C. method produces the highest quality compost. The idea was to process and decompose organic matter as inoffensively and rapidly as possible. No attempt is made to maximize the product's C/N as is done in slower methods developed by Howard at Indore. Most municipal composting done in this country today follows the basic process worked out by the University of California.
Speed of decomposition comes about from very high internal heat and extreme aerobic conditions. To achieve the highest possible temperature, all of the organic material to be composted is first passed through a grinder and then stacked in a long, high windrow. Generally the height is about five to six feet, any higher causes too much compaction. Because the material is stacked with sides as vertical as possible, the width takes care of itself.
