Gardeners often expect composting to be simple and automatic. A new compost heap can actually fail--pile yard debris and add kitchen scraps and nearly nothing happens. A properly active compost heap should be warm--emitting a column of steam in the winter--and giving off the smell of ammonia when turned. If it's cold and smells of garbage, something's missing.
Compost is more than a pile of debris. Compost acts like a living thing--in reality compost is a mix of living things including insects, earthworms, fungi and many kinds of bacteria. A pile of leaves or sawdust will slowly decay on its own but produces little more than fiber for the garden. Leaves or sawdust mixed into an active and balanced compost heap will disappear quickly and become fertilizer. Compost is a community of life that needs all its parts to work efficiently.
A new compost heap of layered debris needs a boost of microscopic life to get started. Inoculants provide that menagerie of living things in the form of fungal spores and dormant bacteria. These organisms have been specially chosen for their ability to digest organic materials. Only a small amount is needed--the organisms quickly multiply in favorable conditions. Once started, all the gardener must do is feed the pile and reap the rewards--clean organic fertilizer.
Like any other livestock, the compost heap needs tending. The heap needs enough water to stay moist but not too much or the pile becomes anaerobic. The most active organisms need a proper balance of air and water. Turning the pile places fresh material in the warm interior where most beneficial organisms flourish. Whenever the heap cools down, turning in fresh debris--a mix of manures and coarse vegetable matter is best--rejuvenates the process. Proper turning exposes dangerous bacteria to the hot parts of the pile, sterilizing many potential problems.
The important parts of finished compost wash away easily. Potassium, nitrogen and other fertilizing elements are water soluble. Finished compost should be covered and stored away from the heap until needed in the garden. Compost has a very mild fertilizing effect even when fresh--application in the growing season has the most effect. The longer a finished heap of compost remains on the ground, the less there is. Earthworms working from the bottom layer eventually turn it all into soil.
For some critical composting applications such as indoor composting toilets, compost inoculants may be wise investments. Compost toilets which don't work properly fill quickly with waste and are not odor free. Start with an inoculant designed for that purpose. For garden compost heaps the best solution is also the cheapest. All the organisms the heap needs are commonly found in healthy active soil. Mix a couple of shovels of good dirt in the heap and save money.