Climatic conditions, particularly temperature, wind, and rainfall, influence the composting operation. The effect of atmospheric temperatures, particularly the lowest temperature at which composting might be satisfactorily done, is not fully known. However, having a larger compost pile in cooler weather will reduce the heat loss.
Temperature
Organic refuse has excellent insulation properties. Research has shown that a steep temperature gradient exits between the outer and inner surface of compost piles. The difference in temperature between the outer and inner parts of the compost pile may be several degrees Fahrenheit difference per inch of material. It seems reasonable to believe that composting can be satisfactorily conducted even during severe freezing temperatures. It is probable that turning is not as advantageous in cold as in warm weather, because there would be a longer temperature recovery period after each turn when the colder exterior of the pile was turned into the interior.
Wind
Strong winds markedly lower the temperatures on the windward side of the compost pile. Two factors play an important role in temperature reduction by winds: (a) the coarseness of the material, which affects the porosity of the pile and the evaporation, and (b) the moisture content. Unshredded or coarsely shredded material has a greater porosity and permits greater penetration of wind into the pile. Consequently, more evaporation takes place, and when the material becomes too dry, bacterial activity is inhibited.
Shredding or grinding to produce a maximum particle size of about 2 inches provides a more homogeneous mass which is not as easilypenetrated by winds. Thoroughly wetting the exterior of the pile, particularly on the windward side, will reduce wind penetration and permit the interior high-temperature zone to extend nearer to the surface of the pile. Wind cooling and drying of compost piles is of little significance when piles or bins are used, since the material is protected on all sides except the top, which wetting will protect.
Rain
Rain usually does not seriously affect composting. If drainage at the bottom of the pile is inadequate, the pile should be finished with a rounded top so that the rainwater can run off. If the compost piles or bins are adequately drained so that water does not stand around the piles and penetrate the bottoms, then a slight depression helps maintain moisture in the pile (and will occur naturally anyway as the material decomposes). Heavy rains accompanied by high winds will penetrate a pile of coarsely shredded material as much as 12 to 15 inches on the windward side, but the resulting effect on large piles can be readily overcome by subsequent turning.
Turning should not be done in the rain, because the material may become waterlogged. If the material cannot be turned on the regular schedule due to rain, it is better to let it become deficient in air for a short time than to have the material soaked. Rainy weather can present more of a problem when composting is done in pits or bins. The top of the pit should be rounded to turn the water, which will, however, seep along the edges to the bottom. The bottom should therefore be adequately drained to remove the water and to allow a minimum of penetration into the compost.
