2008-09-06 / Columnists

The Process Involved With Maintaining a Compost Pile

Nature Notes
By Patricia Martin

Last week, for those of you who read this column regularly, I wrote about fly control, and mentioned that it's not only horse manure and garbage that attracts flies and provides them with breeding sites, but compost and grass piles, as well. These are particularly good breeding grounds for those biting stable flies, particularly if they're not managed properly. This all got me to thinking about compost, and how individual compost piles work.

The City of Mackinac Island has a composting system, which combines yard waste (grass clippings, leaves, weeds, etc.) with manure, ground-up paper, and other organic materials (carbon compounds) like kitchen waste and slop buckets from the hotels. After being turned on a regular basis, this turns into good compost, which we can use in our gardens. As I always say, "We pay to get it taken away, and we pay to get it back again." But individuals on the Island also maintain their own compost piles.

Composting is merely speeding up the natural process of rotting. In fact, the whole world is really one big compost pile, if you look at it that way. Walt Whitman wrote, "It gives such divine materials to men, and accepts such leavings from them at last." In the natural world, things live, die, are broken down, and absorbed again by other living organisms which live and die, and the cycle goes on and on. The word compost itself comes from two Latin words, which mean "together," and "to bring" (the same roots as the words compote). So, in essence, it means you just bring different things together and let them, or help them, rot.

The end product can be used to improve the nutrients in the soil, particularly nitrogen, phosphorus, and potassium, and other micronutrients, which in compost are released at the rate in which plants need them. The organic material in compost binds with soil particles to form clumps, which holds water on their surface so that the plants can use it. This clumping also makes air spaces available in the soil so that roots can grow. Compost adds microorganisms and other creatures that help build soil, and it can also neutralize soil toxins and heavy metals by binding them up. In other words, it's good stuff, and on Mackinac, where our topsoil is so thin, it sure helps the gardens grow.

Most of decomposition, be it in a compost pile or in the woods, is accomplished by microorganisms. For microorganisms to thrive, they need an energy source (carbon), a protein source (nitrogen), moisture, and oxygen (for aerobic bacteria, anyway, which do most of the breakdown). Bacteria are one group of microorganisms that work in rotting things, some of which work at about 55 degrees Fahrenheit, others at 70 to 90 degrees Fahrenheit, and still others that work at more than 100 degrees Fahrenheit, which can actually raise the temperature of rotting materials to 160 degrees Fahrenheit. In addition, fungi and actinomycets (a kind of cross between a bacteria and a fungi) act in breaking down the tough stuff that the bacteria leave behind, like cellulose, starches, proteins, and lignin. Larger organisms also help in the rotting process, including the ever-popular earthworm, and insects.

In a compost pile, because you want to get the microorganisms the things they need to do their job, usually quickly, you need to make sure you provide them with a mixture of ingredients. If you only have one kind of organic material, say leaves, or hay or grass clippings, you will probably have very slow decomposition, because while you've provided plenty of carbon, there is probably not enough nitrogen. If you just pile up a bunch of grass clippings, it will heat up and form a slimy anaerobic mess (with no oxygen). It's a good thing in a compost pile to mix up bulky organic materials, like hay, dried grass, and leaves (good sources of carbon) with animal manure (good source of nitrogen), and you can add natural fertilizer materials, like bone meal, blood meal, and wood ashes. The easy rule of thumb is that you should use about twice as much vegetable matter as animal matter. Organic kitchen refuse is usually a good thing to add to a compost pile, but don't put in any fats, either vegetable or animal, or meat scraps, as they don't break down easily, and they tend to attract animals and flies. Grass clippings are also good, but they should be dried before putting them in a pile, or mixed with other dry absorbent materials, like dried leaves, or thinly layered through the pile. Hay or straw can be added, but they should be weathered first, otherwise a lot of nitrogen gets used up in breaking them down. Leaves break down slowly, unless they're chopped first (running them over a couple of times with a lawn mower works). Oak or beech leaves will make a compost that is more acidic, which is good for blueberries and azaleas. Weeds can be mixed into a compost pile, as long as the pile is large enough to get hot enough to kill all of the seeds, so put them in the center of the pile. There are some things that should not be added to compost piles, including coal or charcoal, colored paper, diseased plants, non-biodegradable items, pet litter, and toxic chemicals.

In starting a compost pile, it helps to have an activator, something that you might think of as a starter or catalyst that gets the microorganisms going. Things like meals (blood bone, alfalfa, or cottonseed), a bit of finished compost, soil, aged and dried manure, or you can buy artificial activators like fertilizers (which aren't particularly effective), or bacterial activators that have bacteria and fungi already in them.

There are whole books written on the "right" way to set up a compost pile, and tons of studies have been done, but there is no single correct way to build one. Some people like to enclose them in wooden fencing, others with screens around them, and still others totally enclosed in barrels that need to be opened and mixed for aeration. There are lots of choices. On Mackinac, there is a city ordinance that if you're putting things other than yard waste in the pile, it has to be enclosed. Check with Kelly Bean at the City office to be sure about regulations.

However you build it, besides supplying carbon and nitrogen sources, the piles need oxygen and water. Piles should generally not be more than five or six feet wide or tall (they can be any length), or the pile may not get enough oxygen into the center. Air can only penetrate from 18 to 24 inches into a pile. Some people put in venting pipes or screens rolled up into a tube to allow for air movement.

Turning the pile speeds up the decomposition time, by mixing the compost material and microorganisms and improving oxygen flow into the pile. Turning also cuts down on the fly breeding problem. If piles are turned at least once a week, it interrupts the development of the fly larvae, and they don't develop. Turning also helps keep the moisture content even. It's a good idea to water the pile as you build it. If rains falls at regular intervals, there may be no need to add more water to the pile. If it doesn't, the pile might need to be watered, perhaps when it's turned. If it's a particularly wet year, you may want to tarp the pile to keep some of the rain off. Covering the pile may also insulate it, so the temperatures get hotter and it breaks down quicker.

There is a lot more to composting, if you want to get into it, but it really doesn't have to be that complicated. All things that were once living will rot, and become compost eventually. Play around with it, and see what works for you. You may decide that you don't want to compost your own yard and kitchen waste, and decide to put all the leaves and grass clippings into clear plastic bags and send it on pick-up day to Paul Wandrie and the men at the Department of Public Works, and let them have the fun of building compost.

Trish Martin is a yeararound resident of Mackinac Island, has earned a master's degree in botany from Central Michigan University, and owns Bogan Lane Inn.

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