Factors Affecting Composting
- Composting saves money, recycles waste, and produces an effective enrichment for soil. Amending garden soil with compost creates a favorable growing environment for plants of all types. Though composting is not a complicated undertaking, several factors that affect the process must be monitored if the end result is to be a horticultural bonanza and not just a big pile of rotting leaves.
- Aerobic microorganisms are the most important agents of decomposition, and they need air. Though open to the air, a compost pile should be turned regularly to aerate material on the bottom and in the center. Compost bins should have vents to ensure air circulation, but again, periodic tossing of the material with a garden fork is recommended. When oxygenation is inadequate, aerobic bacteria die off and anaerobic bacteria take over. Decomposition slows significantly, and the anaerobic bacteria produce odoriferous organic acids which can be harmful to plants.
- Temperature is an important factor in composting. Temperatures between 90 and 140 degrees Fahrenheit are considered optimum for the desired fast decomposition. Lower temperatures slow the decaying process; higher temperatures reduce the activity of all organisms, including helpful earthworms, beetles and ants. In cold climates, wrapping the bin in thermal blankets may help keep the temperature up, and piles can be covered with tarps; however, microbial activity will resume on its own when temperatures rise. Compost thermometers are available for monitoring purposes, but sticking an iron pipe into the center of the pile or bin and feeling it when it is removed will work just as well. As long as the inside of the mass is warm, everything is working.
- Another factor necessary for composting is moisture, and like oxygen and heat, it must be present in the proper amount. Insufficient moisture will cause aerobic bacteria to slow down or become dormant; too much moisture will kill them by depriving them of oxygen. When this happens, the ever-present anaerobic bacteria move in, as they do when oxygen is insufficient, and with the same result: stinky compost. The ideal moisture level is between 40 and 60 percent--the compost should feel damp. If it feels dry, water should be added and mixed in from bottom to top so that moisture is distributed evenly.
- A carbon to nitrogen ratio of 25:1 to 30:1 is considered ideal for rapid decomposition. Dry, brown material, such as leaves and twigs, is rich in carbon; green things, such as grass clippings and kitchen waste, are rich in nitrogen. Insufficient nitrogen will result in material that does not decay. Too much nitrogen will result in the creation of foul-smelling gas and conditions which can kill beneficial microorganisms. A simple rule of thumb is two to three parts brown material to one part green. Mix thoroughly, and if ever the smell of ammonia is noted, cut back on the nitrogen-rich greens.