Though we might like to make our compost piles so large that maintaining sufficient airflow becomes the major problem we face, the home composter rarely has enough materials on hand to build a huge heap all at once. A single lawn mowing doesn't supply that many clippings; my own kitchen compost bucket is larger and fills faster than anyone else's I know of but still only amounts to a few gallons a week except during August when we're making jam, canning vegetables, and juicing. Garden weeds are collected a wheelbarrow at a time. Leaves are seasonal. In the East the annual vegetable garden clean-up happens after the fall frost. So almost inevitably, you will be building a heap gradually.
That's probably why most garden books illustrate compost heaps as though they were layer cakes: a base layer of brush, twigs, and coarse stuff to allow air to enter, then alternating thin layers of grass clippings, leaves, weeds, garbage, grass, weeds, garbage, and a sprinkling of soil, repeated until the heap is five feet tall. It can take months to build a compost pile this way because heating and decomposition begin before the pile is finished and it sags as it is built. I recommend several practices when gradually forming a heap.
Keep a large stack of dry, coarse vegetation next to a building pile. As kitchen garbage, grass clippings, fresh manure or other wet materials come available the can be covered with and mixed into this dry material. The wetter, greener items will rehydrate the dry vegetation and usually contain more nitrogen that balances out the higher carbon of dried grass, tall weeds, and hay.
If building the heap has taken several months, the lower central area will probably be well on its way to becoming compost and much of the pile may have already dried out by the time it is fully formed. So the best time make the first turn and remoisten a long-building pile is right after it has been completed.
Instead of picturing a layer cake, you will be better off comparing composting to making bread. Flour, yeast, water, molasses, sunflower seeds, and oil aren't layered, they're thoroughly blended and then kneaded and worked together so that the yeast can interact with the other materials and bring about a miraculous chemistry that we call dough.
Carbon to nitrogen ratio. C/N is the most important single aspect that controls both the heap's ability to heat up and the quality of the compost that results. Piles composed primarily of materials with a high ratio of carbon to nitrogen do not get very hot or stay hot long enough. Piles made from materials with too low a C/N get too hot, lose a great deal of nitrogen and may "burn out."
The compost process generally works best when the heap's starting C/N is around 25:1. If sawdust, straw, or woody hay form the bulk of the pile, it is hard to bring the C/N down enough with just grass clippings and kitchen garbage. Heaps made essentially of high C/N materials need significant additions of the most potent manures and/or highly concentrated organic nitrogen sources like seed meals or slaughterhouse concentrates. The next chapter discusses the nature and properties of materials used for composting in great detail.
