Managing Your Bins
Step 6. Turning the Piles
On-going monitoring of pile conditions will give you the best indication of when your piles need turning. In general turning piles less produces a higher quality compost with larger and more diverse populations of beneficial organisms, but turning compost piles is necessary for a number of reasons:
- To ensure pathogen and weed seed destruction throughout the entire pile.
- To renew the supply of oxygen throughout the pile, ensuring the pile does not become anaerobic.
- To incorporate fresh materials from the outside of the pile into the center, where they will provide fresh food to organisms and will initiate another rise in temperature.
- To homogenize the blend of materials throughout the pile.
The temperatures in the pile will rise most intensively in the first 2 months of the pile’s life and throughout this hot stage, it is recommended that you turn the pile 3 times. In this first stage of the compost process, there is a high ratio of simple sugars (carbohydrates) present that bacteria feed upon, rapidly metabolizing, reproducing, and producing heat. As temperatures rise, the populations of organisms in the pile change from species which are adapted to ambient temperatures (mesophylic), to species which are adapted to high temperatures (thermophylic).
A large part of compost management is taking advantage of high temperatures while they are present to sterilize the materials in the pile of unwanted organisms. While heat loving organisms become present and active during this stage, they survive only because they are adapted to these specific conditions, where as problem species like plant diseases and E. coli cannot. Once the temperature has reached its peak (at least 131 degrees Fahrenheit for over 3 days) and dropped, turn the outside of the pile to the inside and the inside of the pile to the outside. Repeat this process again, turning the pile after it has reached its peak temperature and you are confident all of the material has been sterilized. The graph on the next page shows the relationship between temperature, pile turning, and simple sugars. After a few turnings most of the simples sugars have been metabolized and the temperature will no longer reach the peaks it did early in the process. The first two turns will probably be done in your first bin and then in the third turn you can simultaneously transfer the pile to a second bin.
Bin Systems – Ideally, your bin system contains at least three bins for composting, as well as space for the storage of dry carbon materials. The bins are designed to be used in succession; each new batch will always start in your first bin, or Bin 1. When Bin 1 is full, its contents are transferred to Bin 2 and a new batch is started in Bin 1. Continue this progression until all of the bins are full, at which point the contents of the last bin will likely be finishing composting ready for curing. Before a new batch is created, the last bin can be emptied and either used immediately or stored elsewhere under cover.
Turning of piles can be done by students, or a parent/staff volunteer. A pitch fork works best if the mix is made of large particle materials, but a shovel can also be used. To involve a large group of students, form a line and let the students take turns shoveling one forkful at a time. If your goal is simply to turn the pile and not transfer it from one bin to another, you can fill a wheelbarrow from the center of the pile, turn the outside of the pile inside and then cover it back up with the contents of the wheel barrow. If you have access to a small tractor or skidsteer, the bin system can be designed so that piles can be turned easily by machine as well. You may find your own creative method for turning and so long as all of the contents of the pile reach the center of the pile and heat you should achieve the conditions to produce good finished compost.