There is no doubt that composting is the heart of modern organic gardening. Though I value the books and other tools I inherited from my grandfather, the most important thing I got from him when he retired was his compost pile. For, while you can buy books or tools, compost must be made. The new gardeners among you may not yet fully appreciate this truth; the old hands certainly will. Compost is like sourdough bread or vinegar starter…it has a history and complexity that takes time to build.
Background on Compost
If you think about it, composting is a form of recycling, as the harvest from many plants is only a small bit of their bulk. For example, we eat practically 100% of a lettuce plant, but the corn or pea seeds that we relish represent at most 10 percent of the plant. By composting the rest of the plant we return that remaining 90 percent to the garden. Seen in this way it is not so surprising that composting would build and maintain long-term fertility in any soil, since its nutrient “savings account” is being constantly added to.
Compost can also rightly be called a culture, because what it contains is not merely a store of nutrients and a mass of the raw materials from which a friable soil can be made and maintained, but also a whole community of organisms (as with sourdough or vinegar) whose activities and interactions are what is primarily responsible for the fertility and productivity of a long-established garden. A handful of compost is like a handful of seed, or a time capsule, in that it stores a microcosm of the garden from whose plants and soil it was made.
The effects of maintaining this “culture” can be quite significant. Scientists working to reestablish forests on eroded, clear-cut slopes of Oregon’s southern Klamath Mountains found that adding less than half a cup of soil from the root zone of a healthy conifer plantation to each planting hole doubled growth and increased survival of transplanted conifer seedlings by 50 percent over the first year. By the third year only those seedlings receiving the “soil culture” were still living. The researchers concluded that it was the wide range of micro-organisms in the healthy soil, specially and specifically adapted to living with the roots of conifers, that made the difference.
Just as we see in the cases of beta-carotene and dried seaweed, natural products and materials are superior to manufactured ones — especially when creating a new garden on depleted or degraded soils — because they contain of complexes of closely related substances, and it is this complexity that confers benefits which the purer, more “efficient” manufactured products simply can’t match.
Comparison of Compost to Synthetic Fertilizers
All this is aside from the cash and resource savings that a compost pile represents. Almost 2 percent of the natural gas consumed in this country is used to manufacture nitrogen fertilizers; there is the equivalent of one-third to one-half gallon of gasoline in every pound of nitrogen fertilizer in terms of the energy consumed. That energy is nonrenewable; once burned, it is gone, and not only unavailable for our further use, but a pollutant that fouls the atmosphere and contributes significantly to climate instability — a great threat to all our garden plans!
What is most wasteful about manufactured fertilizers, though, is that one-third to one-half of the nitrogen and one-fifth of the potassium and phosphorus in them is washed away into our streams, ponds, and groundwater aquifers before plants can use it. There, these nutrients are no longer an asset, but another pollutant that someday must be removed. In fact, nitrate pollution of water supplies is already becoming a serious problem nationwide. Before blaming this entirely on the farmers, consider the aggregate impact of 50,000 suburban homeowners—each dosing his or her parcel of lawn with a combination fertilizer and herbicide—on the underground water supply of even a small city. When you think what happens to a gentle spring rain percolating down through the soils of that average community, it is no surprise that bottled water sells so well!
The energy of a compost pile—the bacterial energy of decomposition, which takes refuse that would otherwise end up clogging the community landfill, and turns it into free fertilizer—is not just renewable, but constantly going on all around us in a never-ending cycle of decay and rebirth. The essence of the organic method is to tap into those natural cycles and let them do the work for us. Because of this, as well as for its obvious material benefits, composting is central to organic gardening.
Nutrient Diversity in a Compost Pile
The more diverse the ingredients that go into a compost pile, the more nutritionally balanced the finished product will be. One of the great advantages of compost over purchased fertilizers is that it’s loaded with concentrated micronutrients. When you shred and then compost the leaves of a shade tree, you are bringing to your garden nutrients collected by that tree from a much greater depth than the vegetables you grow could ever reach. When you compost the household food waste produced in your kitchen you are collecting nutrients that are, literally, from all over the world. And once you’ve brought those nutrients into your garden, composting keeps them there. Keep in mind that this means you should never put anything on your compost pile that has been treated with pesticides. Store bought produce may not represent much of a threat to the community of microorganisms that devour it, but grass clippings from a golf course or park recently treated with pesticides can wreak havoc with your composting operation, so it is best to avoid such materials entirely.
Compost, with its broad range of nutrients. but low apparent “analysis”—that is, the official N-P-K listing, which indicates the immediately available nutrients—is a stable, slow-release fertilizer whose nutrients will not easily wash out. In laboratory experiments, a highly composted soil sample can be drenched with up to seven times its weight in water spread over a dozen washings that mimic ample summer rains, without losing a significant amount of its mineral nutrients. The nutrients in a fertile, friable soil are so tightly bound to the complex soil particle structure that they are released primarily through the chemical transfers initiated by plant roots, not simply dissolved in water and washed away. The standard analysis does not pick them up because they aren’t there in the form that the tests are looking for; they don’t become “available” until the acids and enzymes secreted by plant roots and by the multitude of soil microorganisms make them available, on an as-needed basis.
So while the advocates of quick-acting soluble fertilizers may be technically correct (in the narrowest sense) when they say that plants can’t tell where a given amount of nutrient came from, they miss the point. The efficiency of slow-release, recycled nutrients is simply better, more varied and balanced, and less prone to causing problems than the packaged product. The nutrients are available over a longer period, to be taken up at the plants’ will, without the danger or possibility of overdose, or creation of pollution problems elsewhere. Over time this balanced storehouse of both macro- and micronutrients increases. Of course, organic materials can create problems if used improperly: the runoff from fresh manure, unwisely spread on fields that will not be promptly plowed, can wash into ponds and rivers, polluting them just as quickly and surely as a synthetic fertilizer. Proper materials are only part of the organic method; proper handling of those materials demands equal attention.
Compost, Soil Structure and Carbon Sequestration
Not even the most devoted adherent of bagged fertilizer will claim that it improves soil structure, but compost helps make cold, soggy soils warmer and drier, and yet will help make sandy and gravelly soils more drought-resistant as well, bringing each soil extreme toward that middle ground that most plants favor: a loose, loamy soil with a neutral pH.
It does this by improving what is called the “crumb structure” of the soil. A fertile, friable soil somewhat resembles moist gingerbread. The addition of compost builds this kind of soil not only through its own physical properties, but by the soil life it includes. Tiny, colorless fungi, responsible for the initial stages of decomposition in a compost pile, not only bind soils with their far-reaching, threadlike bodies, but produce elements that bacteria then turn into a kind of glue that causes loose soil particles to clump together into “aggregates.” Many species of soil fungi in this community also directly help plant roots gather food, in exchange for plant foods they are unable to produce for themselves. In addition to that they help “sequester” carbon dioxide (CO2) and thus help prevent CO2 accumulation in the atmosphere, which drives climate change.
Compost and Earthworms
Earthworms are one of the most indispensable inhabitants of both the compost pile and the garden. The mucus coating that makes them feel slimy is what allows them easy passage even through tough soils. This lubricant remains on the walls of their tunnels, binding the soil particles there in the same process of aggregation that is so crucial to good soil structure. Charles Darwin himself studied earthworms closely. As the earthworm eats its way through the material in the compost pile, it mixes the raw materials with its own pH-balancing digestive secretions and the diverse bacterial population of its gut. As a result, earthworm castings are one of the best manures available, and an active earthworm may well produce its own weight in castings daily.
Compost and the Microbial Community of the Soil
Not only are manufactured fertilizers unable to equal this improvement program, this soil-building function despite their higher long-term cost, but they are caustic chemicals and actually degrade the soil, because they kill or drive off the fungi, the bacteria, and the earthworms—all of the beneficial inhabitants that form the soil community of a fertile soil. These valuable residents will return in time; but by using manufactured fertilizer, the bag gardener not only pays out hard-earned cash, but creates a potential pollution problem and sets back the development of a truly fertile garden soil—all for a quick shot of growth. This is even more of a folly during dry periods, because organically fortified soils hold water better in droughty weather and are thus able to continue providing nutrients, while soils with poorer structure, even if fortified with soluble nutrients, cannot pass them on to the plants if there is not sufficient water to dissolve them. After a rain there will be a quick flush of growth as the nutrients are picked up by the water, made temporarily available to the plants, and then just as quickly washed away.