Climatic conditions, particularly temperature, wind, and rainfall influences the composting operation. The effect of atmospheric temperatures, particularly the lowest temperature at which composting might be satisfactorily done, is not known. A slightly larger compost pile in winter weather will reduce the heat loss per unit volume.

Organic refuse has excellent insulation properties. As has been previous shown, a steep temperature gradient exits at the outer surface of compost stacks. The difference in temperature may be several degrees Fahrenheit per inch of material. It seems reasonable to believe that composting can be satisfactorily conducted at severe freezing temperatures, providing snow conditions do not interfere with turning and the snow becomes mixed with the compost. It is probable that turning would not have to be done quite as often 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.

Strong winds markedly lower temperatures on the windward side of the compost pile. Two factors play an important role in temperature lowering 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 that is not as easily penetrated 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. In an area of strong prevailing winds, a windbreak could be built to protect compost piles. This should seldom be necessary, however, since increasing the size of and wetting the pile will control temperatures, and all material will be exposed to high temperatures by turning. 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 usually does not seriously affect composting if the piles are finished with a rounded top so that the rainwater can run off and if the compost piles or bins are adequately drained so that water does not stand around the piles and penetrate the bottoms. 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 regular schedule owing 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. In rainy areas, pits should be lined with concrete, brick, or masonry, and provided with tile drains. Or roofs could be built over the bins or pits to protect them from rain.

During rainy weather, shredding or grinding, and the segregation of the materials should be done under cover. Facilities for storing the incoming materials for a short time should be provided, so that stacking or piling does not have to be done during rain.

Composting can be done satisfactorily in relatively cold climates or in areas of considerable rainfall with a minimum of roofed buildings. Heavy snowfall will greatly hinder continuous composting operations and removal of snow from the composting piles or bins will usually be required. Material will not become anaerobic or create an odor nuisance during really cold weather. Hence, if an ample composting area is available, the material can be allowed to stand for long periods without turning until the weather is favorable.