Making compost from leaves may need some additional nitrogen

by Curtis Smith, PhD, NMSU Extension Specialist

Q. Please give me a formula for making compost with leaves.

Jack C.
Roswell

A. Composting is as much art as science, but knowledge of the science helps the compost artist. Scientific research tells us that the ratio of carbon (carbohydrates) in the leaves relative to the nitrogen (protein) (C/N ratio) should be about 30 parts carbon to 1 part nitrogen for optimal composting. Freshly fallen tree leaves that froze on the tree before falling are very close to that optimum ratio and will compost well if they are shredded and kept moist (even in the winter). Older leaves and those that are brown can have a C/N ratio of 80:1. They will need additional nitrogen to speed decomposition. Leaves will decompose naturally without added nitrogen, but compost will form more slowly. The nitrogen can be added in the form of manure or commercial nitrogen fertilizer (nitrate fertilizer is more effective in cold weather than ammonium fertilizer). Carbon and nitrogen are needed by the fungi and bacteria that decompose the leaves to form compost. When the C/N ratio is optimal the microorganisms multiply most rapidly and consume the leaves quickly.

The C/N ratios of various compostable materials are available in NMSU Extension Publication H-110: Backyard Composting (available online at Backyard Composting).
(continued at SW Yard and Garden Column December 12, 2009)