Leaf Composting

chap2_2Microorganisms need nutrients, primarily carbon and nitrogen, for both energy and growth. The ideal carbon:nitrogen (C:N) ratio is not found in any one organic source. However, it is possible to create compost out of primarily one raw material, such as leaves.

Due to their high carbon content leaves may take 5 months to 2 years to compost by themselves. However, leaves will compost and turn out a good finished product if moisture is adequate and if the pile is turned frequently, ensuring a good supply of oxygen.

Mixing other organic wastes with leaves to utilize these other sources in recycling is important. The high nitrogen source, such as grass clippings or other plant wastes, animal manures, food scraps or other high nitrogen materials can speed up the decomposition process and increase the nitrogen content of the end product making it more suitable for use as a soil amendment. The high nitrogen component must be carefully controlled because the addition of too much nitrogen can result in the formation of ammonia, creating an odor problem. The rapid decomposition also uses up oxygen, causing further problems as the aerobic microorganisms are replaced by anaerobic ones.

Grass clippings are high in nitrogen and can be added to the leaf pile. However, high moisture and high nitrogen content in the grass clippings require that they be mixed into the pile with other materials in order to reduce the anaerobic conditions that can occur from grass being”clumped together” in the pile. Research conducted at Rutgers University by Dr. Peter Strom indicates a mix of 2-3:1 (leaves:grass clippings) as being the optimum for decomposition in the compost pile.

However, as the material decomposes, the problem of maintaining an optimum leaves:grass ratio increases. After leaves are collected in the fall and wind-rowed, they undergo a substantial reduction in volume due to the burst of microbial activity that occurs within the first month of composting. By the time grass clippings are being collected the following spring and summer, the leaves have been reduced in volume as much as 50%.

If leaf/grass clipping mixes are to be composted, leaves collected in the fall should be stockpiled without turning until grass collection begins. At that time, form a pile with the appropriate mix of stockpiled leaves and grass clippings. The leaf piles will likely be anaerobic and some short term odors may be generated when the piles are disturbed.

chap2_11Leaves act as a bulking agent, allowing more oxygen into the windrow to maintain aerobicconditions. Grass clippings, because they are high in nitrogen and moisture provide needed nitrogen and speed the decomposition, and restore vigorous composting activity to pile. Again, experimenting with mixes is a good way to find the mix that works for you.

It should be noted that grass clippings do not need to be removed from the lawn when mowing. If lawns are mowed frequently, and the clippings allowed to fall back into the lawn, their collection is not necessary. Grass clippings, being high in nitrogen, will decompose rapidly and actually return nitrogen to the soil, reducing the need to apply nitrogen in the form of fertilizers.

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