Turning a compost pile involves moving material from the cooler, outer edges and bottom into the hot, active center. This physical act has a singular purpose: introducing fresh oxygen, a process known as aeration. Without this intervention, a large compost pile will quickly slow the natural breakdown of organic matter. The goal is to ensure even decomposition throughout the entire mass.
Why Aeration is Essential
The process of rapid composting is entirely dependent on aerobic microbes, which require oxygen to survive and thrive. These microscopic workers break down organic materials, releasing energy in the form of heat, carbon dioxide, and water vapor. When oxygen levels drop below a healthy threshold, these beneficial microbes begin to die off, and the decomposition rate slows.
A lack of oxygen allows anaerobic microbes to take over, which break down matter much more slowly and produce byproducts like methane and organic acids. This switch results in a cold, sluggish compost pile that often emits a strong, sour, or putrid odor. Turning the pile fuels the aerobic microbes, allowing the internal temperature to reach the thermophilic range, typically between 135°F and 160°F (57°C and 71°C). Maintaining this high heat destroys most weed seeds and harmful pathogens, yielding a safer and higher-quality final product.
Recognizing When the Pile Needs Turning
Several clear indicators signal the need for aeration. The primary signal is a significant drop in the internal temperature of the pile. During the active phase, when decomposition is at its peak, the temperature should be maintained in the thermophilic range to ensure rapid processing.
Once the temperature begins to fall below 135°F (57°C), it indicates that the readily available oxygen has been consumed, and microbial activity is decreasing. A strong, putrid, or sewage-like odor is another clear sign of trouble, as it means the pile has become anaerobic and is producing foul-smelling compounds like hydrogen sulfide. Immediate turning is required to introduce air and stop the production of these undesirable chemicals.
A noticeable reduction in the pile’s overall size is a visual cue that decomposition has been active and the material has compacted. This compaction naturally closes off air pockets, leading to lower oxygen levels deep inside the pile. Acting on these three specific indicators ensures the pile is only turned when it will be most beneficial.
The Physical Process of Turning
Turning requires moving the material that has been cooling and drying on the exterior into the center, where microbial activity is highest. A long-handled pitchfork, a shovel, or a specialized compost crank are the most common tools used. The technique involves a complete reconstruction of the pile, effectively swapping the contents from the outside and bottom with the contents from the center.
Begin by moving the cool, outer layers of material into a new, adjacent pile or a cleared space. These layers, which have not reached the necessary high temperatures, will form the new core of the reassembled pile. As you work, ensure you break up any large clumps of material to maximize the surface area exposed to the new air supply.
During this process, check and adjust the moisture level, which should feel like a well-wrung sponge. If the material appears dusty or too dry, lightly spray it with water as you rebuild the pile, ensuring the moisture is evenly distributed. Conversely, if the pile is too wet and matted, mix in dry, carbon-rich materials like wood shavings or shredded leaves to absorb excess moisture and restore proper air flow. The process is complete when the entire mass has been thoroughly mixed and the cold edges have been incorporated into the hot core.