The Science And Methods Behind Composting

In last week’s column, I discussed the reasons for having your own compost pile or bin (however so humble), what can go into the pile, and how to get it started. This week, let’s take a look at the seemingly magical hocus pocus of science that makes composting work—and how to make it work best for you.Keep in mind, though, that no property and no garden is too small for composting.

In constructing a compost pile, there should be enough organic materials available to make a minimum of six to seven layers. Such bulk is necessary to reduce moisture evaporation and to maintain optimum temperatures for decomposition.

Remember that the very best compost piles are ones that have the right ingredients, to the right depths, that will allow proper “cooking.” It’s this cooking that not only decomposes the organic materials but also kills harmful diseases and most weed seeds. You can buy thermometers with long probes that are designed just to measure the temperature inside your heap; they cost less than 20 bucks.

Be sure not to pack the materials down too tightly, as circulation of air will be reduced and decomposition slowed.

Remember that a once a compost pile has been constructed, it will require some attention to assure rapid decomposition. An active pile will tend to shrink. Additional organic materials should be added during the season in order to sustain the pile’s bulk, or mass.

Be sure that materials added to the pile are well mixed—finer materials like grass clippings or shredded matter should be blended with coarser materials like leaves, weeds or hay. This will allow air to diffuse throughout the pile and reduce compacting problems. Moisture should be added, especially during the hotter part of the summer and into the fall if it remains dry. Dish out the center of the pile so water will seep in rather than run off.

Occasionally, it’s helpful to fluff or loosen the pile with a pitch or tined fork or special turning tool to allow for better air and moisture penetration. If you follow these and the above directions, it should not be necessary to turn the pile, as was once the common practice.

Normally, this “scientific” composting process will take two to three months to produce humus. The older layers at the bottom of the pile will be the first ones to convert to humus. Twenty to 30 layers, each about 8 to 10 inches thick, will produce 1.5 to 2 feet of humus. When late summer arrives, remove the enclosure or compost bin, rake off the dried materials, and the rich humus is ready to use.

It’s important to remember, though, that if the pile is improperly cared for, it can sit for years and years and do absolutely nothing. The pile can also overcook (to over 140 degrees)—and that can be as bad as a pile that doesn’t cook at all.

One of the most common problems in composting is allowing the pile to dry out, particularly during the hotter part of the summer. Without enough moisture, microorganisms become dormant and decomposition ceases. Proper moisture in the pile is necessary for the metabolism and reproduction of these organisms, which are directly responsible for the decomposition process.

Although precise levels vary with the nature of the materials being composted, research shows that moisture content should lie between 40 and 60 percent by weight. A time-tested rule of thumb: Let your working compost pile approximate the dampness of a squeezed-out sponge.

The organisms involved in aerobic composting require relatively large amounts of atmospheric oxygen. Tests have shown that air will penetrate a properly constructed and maintained pile about 24 inches from all directions that are exposed to the atmosphere. Given the 3-foot diameter of many of the ready-made compost bins, and the fact that the pile shrinks as the bacteria “chew up” the material, atmospheric oxygen is increasingly able to penetrate the pile. A wide spectrum of soil microorganisms (bacteria, molds, fungi, actinomycetes, enzymes, etc.) function in the pile as nature’s digestive system.

To create ideal composting conditions, which now seldom occur in nature because of man’s long inhumanity to the soil, there must be present the correct families of microorganisms, in the proper proportions, to trigger the decomposition process. It is here where some of the commercially available compost activators may be helpful to you, as they will take the “pot luck” out of the process by adding all of the necessary microbes. (That having been said, though, I’ve never used them.)

These “activators” contain three basic constituents: bacteria, enzymes and fungi. Bacteria are the most abundant of the micros and can be broken down into two general types: aerobic bacteria, which must have oxygen to function; and anaerobic bacteria, which function without atmospheric oxygen. Both broad families must be present in high numbers if the decomposition is to be rapid and complete. Leaves, particularly, demand aerobic bacteria for decomposition because of the high percentage of lignin, a substance quite resistant to composting, especially in oak leaves.

Enzymes are a critically important element of the soil. Enzymes are natural organic substances produced by the bacteria themselves to break down the complex carbohydrates into simpler forms that the bacteria can use as food. Thus, the bacteria which contribute to composting are not necessarily self-starting—the enzymes must be present first.

There are two basic families of enzymes that work on organic vegetable wastes: cellulase enzymes, which attack cellulose (wood and plant fibers), and hemicellulase enzymes.

Fungi are the microorganisms that are particularly important in the protracted breakdown of cellulose and lignin after the faster-acting bacteria have made their initial inroads on these resistant materials, and they are important in the soil-making nutritive substances more assimilable to plant roots.

If, once starting your pile, you run into problems, consider the following: Is there a lack of moisture? Over-watering can cause unpleasant odors as a result of killing off aerobic bacteria and resulting in fermentation. Over-watering also can lead to compacting, though rain water rarely will cause problems.

An improperly activated pile will sit, and sit, and must be re-piled (layered) and reactivated. Some smaller compost piles can freeze up in the winter and then are slow to start up in the spring. Larger compost piles can be seen letting off steam in the dead of winter.

Microbes become much less active at temperatures below 40 degrees. To get the pile going faster in the spring, add a cup of sugar to the pile.

Finally, remember that at times your compost may become dry enough to become flammable. Never add ashes from a wood stove or fireplace unless you are absolutely, positively sure they are dead cold. As a child, I inadvertently added some ashes to a compost pile after the fire had been out for many hours. That evening, the compost pile erupted into flames and required a response from the local fire department—which was very exciting, but my father was not amused.

So, save those baseball bat-sized zucchinis, the diseased tomato plants, grass clippings, lawn rakings, kitchen scraps, fallen apples, and other terrestrial flotsam and jetsam. Build your compost pile, or buy an easy-to-use compost tumbler, and create your own backyard gold.

For some great additional information on composting, Cornell has a great 12-page fact sheet with helpful diagrams and pictures that you can find at http://bit.ly/2jkv7sU.

Keep growing!