Contrary to modern myths, composting isn't complicated. Learn the composting facts and keep it simple.
It is a tribute to composting that humans have taken such a simple, natural process and elevated it through myth and misunderstanding into a form of New Age alchemy. The spread of these myths has been facilitated by word of mouth, misguided publications from solid-waste managers, and worst of all, hardcore marketing. In order to keep composting simple and inexpensive, let's dispel the composting myths with composting facts.
There are scores of weird and wonderful commercial designs available, from black plastic cubes with deluxe sliding doors to rotating drums to freewheeling spheres. The prices range from tens to hundreds of dollars. These appliances are not essential, of course, but they can accelerate the compost process significantly and can save some labor. Heaps or piles work just fine, however. If you want to keep your pile tidy, consider using wire mesh, or reusing scrap lumber, shipping pallets, cinder blocks, or snow fencing. Dry-climate composters might consider using a covered bin to reduce evaporation and moisture loss, while urban composters may decide to contain their compost in sturdy bins with lids, bases, and small apertures to keep out pests. (A perforated metal trash can is an excellent choice for city dwellers.) If you want a prefabricated bin, consider volume before you buy: more money often buys less capacity; the highest capacity models generally sell for less than $40.
These bacteria-laden powders and liquids are the snake oil of composting. While they do contain "cultured" strains of bacteria and other additives, the fact is that special inoculants are unnecessary. Recent studies suggest that there are approximately 10 trillion bacteria in a spoonful of garden soil. Every fallen leaf and blade of grass you add to your pile is already covered with hundreds of thousands of bacteria — more than enough to do the job.
There are a number of recommended additives for boosting compost performance, most of which are unsubstantiated or silly. Some practitioners suggest pouring Coca-Cola into the pile to increase biological activity; it will increase, but mostly in the form of yellow jackets and ants. Adding yeast is also a common practice, but expensive and useless. Adding worms or worm cocoons has grown in popularity due to some confusion with vermicomposting. Worms do a tremendous amount of good, but need not be purchased or transplanted by the average backyard composter. Just build a pile and they will come.
Adding fertilizer to increase the nitrogen content of a pile is wasteful and expensive. More importantly, synthetically derived fertilizers contain high salt levels and other compounds (perhaps even pesticides, which are harmful to worms and microorganisms; they may impair the nitrogen-fixing ability of the bacteria and short-circuit the nitrogen cycle. If you feel that you must add nitrogen, perhaps to a pile made up of only carbon-rich leaves, always try to use organic sources first: spent grounds from a coffee shop, a neighbor's grass clippings, agricultural manures, or dried blood.
Many gardeners with a high proportion of acid-rich materials to compost mistakenly add lime to their pile to produce compost with a balanced pH. Unfortunately, adding ground limestone will turn your compost ecosystem into an ammonia factory, with nitrogen rapidly lost as a noxious gas. Finished compost is almost always nearly neutral.
A properly built and managed compost pile should smell like the humus-sweet duff of a forest floor. Odors result primarily from mistakes: trying to compost grass clippings by themselves, adding too many food scraps (or the wrong types of food) and allowing too much water to get into the pile or too little air, both of which lead to anaerobic conditions.
Compost piles almost never attract pests if they contain only yard trimmings. Properly constructed compost piles fall well behind bird feeders, outdoor pet food bowls, pet feces, and trash containers as rodent attractors. Adding food to your pile will make it somewhat more attractive to pests, but only if you manage scraps improperly — by dumping them on the top of a pile or bin, for example. But because pests are more problematic in urban areas, composters there might want to avoid adding food altogether or to use a worm box or a completely enclosed bin. In fact, some composters in dense urban areas find that an enclosed compost bin is necessary even when they're composting just yard trimmings.
Building a compost pile by layering browns/greens/browns/greens — then leaving your bin in a nice, orderly lasagna style — will lead to layers of anaerobic activity where the greens (nitrogen-rich, wet) are clumped together and little activity at all where the browns (carbon-rich, dry) are clumped together. If you're building a pile all at once, throw in an armful of browns, then an armful of greens, and add a little water as you go if your materials are dry. Then mix, stir, and fluff after every few additions for a hardworking compost stew.
A number of magazine ads have hood-winked well-intentioned gardeners into thinking that they must produce compost in 14 days. Such expectations are unrealistic and unworthy. Decomposition takes time. While producing compost quickly has some merit, no one should feel compelled to purchase chipper-shredders or other elaborate equipment. In fact, even if material looks like compost after several weeks, it still requires an additional one-month maturation period before it should be used in the garden.
For years, books, periodicals, and composting brochures have obsessed on carbon-to-nitrogen ratios. Regrettably, the arcane charts, tables, and formulas provided overwhelm many gardeners. In truth, compost piles thrive when different types of material (moist and dry, green and brown) are mixed together. And while ratios are fine for compost hobbyists, regular gardeners need only remember that all organic materials will compost in time given some prudent attention.
Joe Keyser contributes regularly to the Brooklyn Botanic Garden Web page.