Convective Air Flow

Bernalillo County Extension Master Composters

Drawing showing convective air flow in a compost pile
Drawing by our very own Jenn Myers.
Please click to see a larger, higher-resolution version.

The high desert composter who manages evaporative loss from a composting setup will be successful. Moisture should be maintained at 50-60% throughout the decomposition process. (This is comparable to freshly-brewed coffee grounds, saturated but not dripping.) Low porosity bins, that is, bins with only a few air intake holes, are quite useful. See Homemade Compost Bins For the Desert for photos of such bins and instructions for making them yourself.

Air flow in a low porosity bin is accomplished with coarse bulking materials which decrease compaction of the wet organic materials and allows for convective air flow throughout the pile. The following may be used as bulking material: finger size sticks, twigs, pine cones, chopped corn and sunflower stalks and corn cobs. In the drawing, the blue arrows indicate the upward movement of air (chimney effect) in a bulked pile. Initially, 6 to 12 inches of coarse material is added to the bottom of the bin. Then layers of moist greens and browns are added. After every 5 inches of greens and browns, then sprinkle 2 to 4 inches of bulking on top of that layer. Do not compact or push down on any layer as this will obliterate the air spaces. Continue this method as you build the pile. So, bulk as you build. When you are finished working, drape the top of pile with a non-porous cover. A piece of plastic will do. This deceases upward evaporative losses.

It may be useful for you to read our Composting in the Desert brochure.

Contact us at compost-questions@nmcomposters.org if you have questions.