May 26, 2012

1 - Lack of water and improper balance of carbon and nitrogen containing materials are a common cause of slow composting in New Mexico.

Yard and Garden May 26, 2012


I have been putting garden trimmings and kitchen waste into my compost pile since January. It does not seem to be decomposing and making compost very quickly. When I turn my compost, I still see some of the vegetables I put into the compost several months ago. Is it too hot for the compost now?

-Billie J. Socorro


It is not too hot. When the decomposer organisms in compost are functioning properly, they can raise the internal temperate of the compost to over 160 degrees.

For compost to decompose at an optimal rate, there must be a proper balance of carbon containing materials and nitrogen containing materials. The optimal ration is about 1 part nitrogen to 30 parts carbon. Kitchen wastes are high in nitrogen as is manure, green grass and weed trimmings. Dry leaves, straw, and wood chips are very high in carbon. If the balance of carbon to nitrogen is not optimal, composting will occur more slowly, but it will happen.

A common problem with composting in New Mexico is that the compost dries quickly. Adequate moisture is needed to maintain the action of decomposing organisms. If the material in the compost is too coarse, the pile can dry quickly, so water or wet compostable materials should be added frequently. The center of the compost pile may be waterlogged while the edges are too dry. This is one of the reasons that frequently turning and mixing the compost pile is important. In both the dry areas and the waterlogged areas composting slows significantly. Turning to mix the materials on a regular basis helps avoid this problem.

If drying winds are a problem, you can use old boards, plastic, or any other material around the sides of the compost to reduce water loss due to wind. Be sure to choose a material that will not interfere with adding new material or turning the compost. Another way to help maintain moisture in the compost and enhance the rate of composting is to grind kitchen wastes in a blender full of water. This ground-up material and water can be added to the compost pile. The finely chopped kitchen wastes will coat other material in the compost pile and, because of their small particle size, will allow very rapid composting. Adding finely ground material increases the water holding capacity of the composts and makes turning the compost even more important.

You can find more information about composting and the carbon to nitrogen ratios of compostable materials in the NMSU Extension Publication - Guide H-110: Backyard Composting.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

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