Yard and Garden: Composting Leaves



AMES, Iowa – Composting is a relatively easy, inexpensive procedure yielding valuable humus that can be returned to garden soil, or used as mulch around landscape plantings. Horticulturists with Iowa State University Extension and Outreach give tips on composting yard wastes. To have additional yard and garden questions answered, contact the ISU Hortline at 515-294-3108 or email hortline@iastate.edu.

How can I accelerate the decomposition of leaves in my compost pile?

Leaves contain high levels of carbon and small amounts of nitrogen. The microbes that decompose leaves and other types of organic matter require nitrogen for their own metabolism and growth. A compost pile composed mainly of leaves decomposes slowly because the leaves don’t contain adequate levels of nitrogen for the microbes.

To promote decomposition, mix leaves with grass clippings or other materials high in nitrogen. If possible, shred the leaves prior to composting. The smaller the size of the material, the faster it will decompose.

Construct the compost pile in layers. Each 6- to 8-inch-layer of plant material should be topped with 1 inch of soil or compost. A small amount of an all-purpose garden fertilizer, such as 10-10-10, can also be added to supply nitrogen to the microbes. Continue to build the compost pile in layers until it is 3 to 5 feet high.

Finally, water the pile regularly and turn it about once every two weeks.

Can I put disease-infested plant material in my compost pile?  

Temperatures of 150 to 180 degrees Fahrenheit are required to kill most plant disease pathogens. Unfortunately, the internal temperatures of most home compost piles don’t reach this level and the disease organisms are not destroyed. For many home gardeners, it’s best to bury or haul away diseased plant material.

Do I need to add an activator to my compost pile?

It is not necessary to add an inoculant or activator to a compost pile. A compost pile should be composed of layers of plant material and soil or finished compost. The soil and finished compost contain the microbes that will decompose the plant material. When constructing a compost pile, also add some fertilizer or manure. Nitrogen accelerates the decomposition process if the plant materials are high in carbon. 

How long does it take a compost pile to break down?

The rate of decomposition depends upon the composition of the compost pile, level of management and other factors. A well-managed compost pile (one that is watered and turned regularly) containing a mixture of shredded plant material should be ready in two to four months. A good compost pile contains a mixture of green materials, such as grass clippings, and dry materials like leaves and straw. Compost piles composed of unshredded materials and left unattended may take a year or longer to decompose. The timing of compost pile construction is another important factor. Compost piles prepared in fall will not be ready until early summer of the following year. Compost piles constructed in spring should be ready in mid to late summer.

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