Look on the shelves of almost any store or in any catalog selling plants and gardening equipment and you'll find "compost activators" offered. These mixtures contain beneficial microorganisms, nutrients, and/or more esoteric substances meant to speed composting or improve the quality of the finished compost.
Despite the beneficial organisms and nutrients they contain, however, compost activators are generally neither needed nor cost-effective. If you could take a microscope to the pea vines, old delphinium stalks and lettuce plants tossed onto a compost pile, you'd see they are already seething with microorganisms, just what's needed to get decomposition underway. As raw materials are piled together, these microorganisms get to work and rapidly multiply, as long as they also have sufficient moisture and air.
What does a compost pile need?
Composting microorganisms are most hungry for the elements carbon and nitrogen, the ideal being a ratio of about 15 parts carbon to 1 part of nitrogen. (This need is analogous to our own caloric needs mostly for carbohydrates, which are high in carbon, and protein, which is high in nitrogen.)
Carbon as a compost food comes from bulky, old plant material, such as straw, hay, autumn leaves, wood chips, and old weeds and garden plants. It would be impossible to stuff suitable quantities of any of these materials in a box of "compost activator."
Nitrogen could be squeezed into a box but could also be added by sprinkling nitrogen fertilizer or layers of manure on the pile as it grows. Young, succulent weeds and garden plants (such as thinnings of excess carrot seedlings) and kitchen scraps are also high in nitrogen. Sprinkling the contents of a box of compost activator on a compost pile is an expensive way to supply nitrogen, and brings no special benefits beyond what the above-mentioned materials would bring.
No need to get too exacting about ratios of nitrogen and carbon because they are influenced by such things as the form of the nutrients and the particle sizes of the materials that carry them.
Keep tabs on progress
Monitor the progress and health of your compost pile with your eyes and your nose - your eyes preferably on a thermometer. As long as the materials are moist, a pile that doesn't heat up indicates insufficient nitrogen or excess carbon. A pile that smells bad signals the opposite. Either condition can be corrected by adding the needed nitrogen or carbon materials.
Or by giving it time. A pile deficient in nitrogen, or built slowly over a long period, may never get hot but, in time, will turn to rich, brown compost. Be patient.
The only compost piles that might be candidates for compost activators would be those oddball piles built almost exclusively of offbeat materials, such as sawdust, or with a lot of plant debris that had been heavily sprayed with pesticides. Such piles could lack the necessary organisms, temporarily at least (sawdust alone is severely deficient in nitrogen). Even then, some soil and fertilizer would likely serve just as well.
So pay attention to the ratio of the various things you add to your compost pile, and then watch and smell what happens. Whatever you do, don't fret too much over details. Any pile of organic materials, kept moist, will eventually turn to compost. - Lee Reich, Associated Press (AP)