Compost Myths: To Turn Or Not To Turn, That Is The Question
From The Humanure Handbook by Joseph Jenkins
What is one of the first things to come to mind when one thinks of compost? Turning the pile. Turn, turn, turn, has become the mantra of composters worldwide. Early researchers who wrote seminal works in the composting field, such as Gotaas, Rodale, and many others, emphasize turning compost piles, almost obsessively so.
Much of compost's current popularity in the West can be attributed to the work of Sir Albert Howard, who wrote An Agricultural Testament (1943) and several other works on aspects of what has now become known as organic agriculture. Sir Howard's discussions of composting techniques focus on the Indore process of composting, a process developed in Indore, India, between the years of 1924 and 1931. The Indore process was first described in detail in Sir Howard's work (co-authored with Y. D. Wad), The Waste Products of Agriculture, in 1931. The two main principles underlying the Indore composting process include: 1) mixing animal and vegetable refuse with a neutralizing base, such as agricultural lime; and 2) managing the compost pile by physically turning it. The Indore process subsequently became adopted and espoused by composting enthusiasts in the West, and today one still commonly sees people turning and liming compost piles. For example, Robert Rodale wrote in the February, 1972 issue of Organic Gardening concerning composting humanure, "We recommend turning the pile at least three times in the first few months, and then once every three months thereafter for a year."
A large industry has emerged from this philosophy, one which manufactures expensive compost turning equipment, and a lot of money, energy, and expense goes into making sure compost is turned regularly. To some compost professionals, the suggestion that compost doesn’t need to be turned at all is utter blasphemy. Of course you have to turn it — it’s a compost pile, for heaven’s sake.
Or do you? Well, in fact, NO, you don’t, especially if you’re a backyard composter, and not even if you’re a large scale composter. The perceived need to turn compost is one of the myths of composting.
Turning compost potentially serves four basic purposes. First, turning is supposed to add oxygen to the compost pile, which is supposed to be good for the aerobic microorganisms. We are warned that if we do not turn our compost, it will become anaerobic and smell bad, attract rats and flies, and make us into social pariahs in our neighborhoods. Second, turning the compost ensures that all parts of the pile are subjected to the high internal heat, thereby ensuring total pathogen death, and yielding a hygienically safe, finished compost. Third, the more we turn the compost, the more it becomes chopped and mixed, and the better it looks when finished, rendering it more marketable. Fourth, frequent turning can speed up the composting process. Since backyard composters don’t actually market their compost, usually don’t care if it’s finely granulated or somewhat coarse, and usually have no good reason to be in a hurry, we can eliminate the last two reasons for turning compost right off the bat. Let’s look at the first two.
Aeration is necessary for aerobic compost, which is what we want. There are numerous ways to aerate a compost pile. One is to force air into or through the pile using fans, which is common at large-scale composting operations, where air is sucked from under the compost piles and out through a biofilter. The suction causes air to seep into the organic mass through the top, thereby keeping it aerated. However, this air flow is more often than not a method for trying to reduce the temperature of the compost, because the exhaust air draws quite a bit of heat away from the compost pile. Mechanical aeration is never a need of the backyard composter, and is limited to large scale composting operations where the piles are so big they can smother themselves if not subjected to forced aeration.
Aeration can also be achieved by poking holes in the compost, driving pipes into it, and generally impaling it. This seems to be popular among some backyard composters. A third way is to physically turn the pile. A fourth, largely ignored way, however, is to build the pile so that tiny interstitial air spaces are trapped in the compost. This is done by using coarse materials in the compost, such as hay, straw, weeds, and the like. When a compost pile is properly constructed, no additional aeration will be needed. Even the organic gardening pros admit that, “good compost can be made without turning by hand if the materials are carefully layered in the heap which is well-ventilated and has the right moisture content.” 45
This is especially true for “continuous compost,” which is different from “batch compost.” Batch compost is made from a batch of material that is composted all at once. This is what commercial composters do — they get a dumptruck load of garbage or sewage sludge from the municipality and compost it in one big pile. Backyard composters, especially humanure composters, produce organic residues daily, a little at a time, and rarely, if ever, in big batches. Therefore, continuous composters add material continuously to a compost pile, usually by putting the fresh material on the top. This causes the thermophilic activity to be in the upper part of the pile, while the thermophilically “spent” part of the compost sinks lower and lower to be worked on by fungi, actinomycetes, earthworms, and lots of other things. Turning continuous compost dilutes the thermophilic layer with the spent layers and can quite abruptly stop all thermophilic activity.
Researchers have measured oxygen levels in large-scale windrow composting operations (a windrow is a long, narrow pile of compost). One reported, “Oxygen concentration measurements taken within the windrows during the most active stage of the composting process, showed that within fifteen minutes after turning the windrow — supposedly aerating it — the oxygen content was already depleted.” 46 Other researchers compared the oxygen levels of large, turned and unturned batch compost piles, and have come to the conclusion that compost piles are largely self-aerated. “The effect of pile turning was to refresh oxygen content, on average for [only] 1.5 hours (above the 10% level), afterwhich it dropped to less than 5% and in most cases to 2% during the active phase of composting . . . Even with no turning, all piles eventually resolve their oxygen tension as maturity approaches, indicating that self-aeration alone can adequately furnish the composting process . . . In other words, turning the piles has a temporal but little sustained influence on oxygen levels.” These trials compared compost that was not turned, bucket turned, turned once every two weeks, and turned twice a week. 47
* Compost Myths: To Turn Or Not To Turn, That Is The Question is from Chapter 3 of The Humanure Handbook by Joseph Jenkins. ©1999 Joseph C. Jenkins. All rights reserved. Used with permission. Joseph C. Jenkins (1999). The Humanure Handbook: A Guide To Composting Human Manure, 2nd Ed. Jenkins Publishing, PO Box 607, Grove City, PA 16127. To order, phone: 1-800-639-4099 | www.jenkinspublishing.com