Organic Gardener's Composting by Steve Solomon

_Moisture. _A dry pile is a cold pile. Microorganisms live in thin films of water that adhere to organic matter whereas fungi only grow in humid conditions; if the pile becomes dry, both bacteria and fungi die off. The upwelling of heated air exiting the pile tends to rapidly dehydrate the compost heap. It usually is necessary to periodically add water to a hot working heap. Unfortunately, remoistening a pile is not always simple. The nature of the materials tends to cause water to be shed and run off much like a thatched roof protects a cottage.

Since piles tend to compact and dry out at the same time, when they are turned they can simultaneously be rehydrated. When I fork over a heap I take brief breaks and spray water over the new pile, layer by layer. Two or three such turnings and waterings will result in finished compost.

The other extreme can also be an obstacle to efficient composting. Making a pile too wet can encourage soft materials to lose all mechanical strength, the pile immediately slumps into a chilled, airless mass. Having large quantities of water pass through a pile can also leach out vital nutrients that feed organisms of decomposition and later on, feed the garden itself. I cover my heaps with old plastic sheeting from November through March to protect them from Oregon's rainy winter climate.

Understanding how much moisture to put into a pile soon becomes an intuitive certainty. Beginners can gauge moisture content by squeezing a handful of material very hard. It should feel very damp but only a few drops of moisture should be extractable. Industrial composters, who can afford scientific guidance to optimize their activities, try to establish and maintain a laboratory-measured moisture content of 50 to 60 percent by weight. When building a pile, keep in mind that certain materials like fresh grass clippings and vegetable trimmings already contain close to 90 percent moisture while dry components such as sawdust and straw may contain only 10 percent and resist absorbing water at that. But, by thoroughly mixing wet and dry materials the overall moisture content will quickly equalize.