GROUNDS MAINTENANCE/Site selection and process affect compost quality

Many states, and an increasing number of cities and counties, are requiring yard waste to be composted. For residents, that means bagging leaves separately in paper bags rather than disposing of them with the rest of the household trash. For local governments, it means providing a resting place where leaves can be properly composted.

The selection of a composting site can be difficult. Cities and counties must choose sites that do not draw neighborhood complaints and that can handle the possibilities of leachate and odors. The sites should be gently sloping, and surface drainage should go into a settling lagoon prior to joining normal runoff. They also should be large enough to allow equipment to maneuver when building and turning the windrows of composting leaves.

Composting is not a difficult process, but it can be made even easier. Initially, leaves should be piled in double rows so that, when they are turned over the first time, the twin rows are combined into one row. (The process is accommodated by the rapid amount of leaf size reduction that occurs in the first month of composting.)

Shredding the leaves by mowing or running them through a shredder prior to composting can reduce the volume by as much as half. A compactor also can help in volume reduction.

Several options exist at composting sites. For instance, a 14-day compost process is useful for small amounts of yard waste. The process uses a rotating barrel that contains fresh green grasses and leaf clippings and is rotated every two to three days.

Leaves also can be put into a large pile and left without any management. However, an unmanaged pile of leaves requires two to three years to compost and will involve anaerobic decomposition, which creates odor problems once the pile is moved.

The most efficient composting process involves air, turning, water, bacteria, heat and nutrients.

• Air

  Leaves should be loosely stacked in windrows to allow oxygen flow, which permits aerobic composting. The composting process becomes anaerobic if there is no air flow.

• Turning

  The piles should be turned when the composting operation is finished in the center of the windrow, a process that can range from four days to four weeks. If the compost site is located in a residential neighborhood, the piles should be turned on a rainy day so that odor is not a concern.

• Moisture

  A sprinkler may be necessary to supplement rainfall and ensure that the leaves remain wet — but not dripping.

• Bacteria

  Commercial bacterial compost starters are available, but mixing the leaf piles with previous years’ compost will accomplish the same thing. If the same site is used every year, bacteria can be obtained by scraping the top inch or two of soil off the ground when turning the pile over.

• Heat

  Optimum composting temperature is 140 F (60 C). When the temperature at the center of the pile reaches 100 F (38 C), the compost action has finished, and the pile can be turned. As the pile is turned, the leaves at the outside of the pile should be moved into the center of the new pile, and the center leaves should be moved out to the edge. Maintaining the optimum temperature should be no problem in the summer months. However, composting in winter requires a deep outer layer of leaves to provide insulation for the center of the pile.

• Nutrients

  Nitrogen is essential for feeding the composting bacteria, and the best sources of nitrogen are manure, weeds, grass clippings, aquatic weeds and commercial nitrogen fertilizer. All, except fertilizer, also provide the heat required for composting.

• During the composting process, the pH value fluctuates from acidic in the beginning to neutral at completion, regardless of the plant products being composted. The idea that pine needles make compost acidic is a myth.

  When the composting process is completed, the pile should be cured for a month to stabilize it. Any leftover ammonia in the material will be converted to nitrate, and the nutrients will be released to plants. If the composting process has not finished, the ammonia will be consumed by bacteria.

  The finished product can be used as an inch-thick, dark mulch in the spring. Compost also can be used to top-dress lawns and can be mixed in equal amounts with loam and sand to create new loam. Many local governments either sell or give surplus compost to residents.

  Successful leaf composting operations require careful attention to the product, to planning the site, to the collection system, to management of the materials, and to use of the end-product. But the results are worth the effort. A difficult landscape product is rendered useful, and the environment receives a major benefit.

  Len Phillips, editor, City Trees, the journal of the Society of Municipal Arborists; [email protected].