Features and Occasionals

Backyard Composting

By Staff

During the growing season, 30% or more of landfill waste is organic yard refuse. Home composting of yard and garden trimmings eases landfill problems and “recycles” these organics into a valuable soil amendment. The benefits of using compost as a soil amendment include increasing soil tilth, fertility, water holding capacity, aeration and drainage.

Composting is the aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms under controlled conditions. Bac­ter­ia start the process and are responsible for much of the decomposition work. Their metabolism creates the heat of the compost pile. Fungi, protozoans, earthworms, centipedes, beetles and millipedes assist the bacteria in breaking down plant tissues. During composting, microorganisms consume oxygen while feeding on organic matter. Active composting generates considerable heat, and large quantities of carbon dioxide (CO2) and water vapor are released into the air. The CO2 and water losses can amount to half the weight of the initial materials.

What happens during composting

Composting begins as soon as the raw materials are mixed together. During the initial stages, oxygen and the easily degradable components are rapidly consumed by the microorganisms.

The temperature of the pile is directly related to microorganism activity and is a good indicator of what’s happening inside the pile. The temperature generally follows a pattern of rapid increase to 120-140 degrees F., where it’s maintained for several weeks depending on conditions. As active composting slows, temperatures will gradually drop until the compost reaches ambient air temperatures.

Steps for a successful compost

The composting process is affected by the site, container type and size, raw materials, and the amount of water and oxygen in the materials.

Step 1 – Select Composting Site

A compost pile should be exposed to at least six hours of sunlight each day. The location should not detract from the landscape. Water should be readily available. Good drainage is important: Standing water can impede the decomposition process.

Step 2 – select compost container

Consider the amount of time and space you have, and the quantity of materials you will be composting. Most compost containers fall into one of these categories: heaps (simple stacked piles), hoops (caged en­closures), bins (boxed enclosures), and barrels (drum enclosures).

For fast, hot compost, the ideal pile size is one cubic yard (3 feet x 3 feet x 3 feet). This volume effectively retains the heat generated by the bacteria. The volume of a single pile should not exceed two cubic yards in order to maintain proper ventilation. If space is a limiting factor, the pile sides can be insulated so that higher temperatures can be maintained in a smaller volume.

Heap it (no cost, good if you have ample space) Simply pile your materials in heaps, ideally at least one cubic yard in volume. If well constructed, heaps are good for “no turn” composting. Just leave the pile for several months or more.

Hoop it (low cost, tidier than heaps) Woven wire mesh or fencing make good enclosures and keep the pile tidy. If you secure it with hooks or twists of wire, you can undo the hoop, set it up next to the pile, and turn the pile back into the hoop in its new location.

Box it (looks good, easy to cover, low to moderate cost) You can use almost any type of scrap or new lumber, bricks or cinderblocks to build an attractive and functional bin for compost. Make sure to leave spaces in the sides for air to get through. Make the front removable for easy access to turn or retrieve the compost. Constructing several bins side-by-side makes it easier to turn the compost.

Barrel it (good for limited space, easy turning, moderate to high cost) You can make one, or buy ready-made. Usually these systems are equipped with a stand and rollers to facilitate turning. Some people just roll their barrel around the yard to achieve the same effect.

Step 3 – Select raw materials:

Almost all natural, organic material will compost, but not everything belongs in the compost pile. Some wastes attract pests; others contain pathogens that can survive the compost process.

Most natural yard and food materials are acceptable except meats, bones, large branches and dairy. Also avoid pet wastes (unless your pet is a bird, horse, rabbit, bat or cow), and plastics and other synthetic products.

Branches, twigs and paper, can take up to two years to decompose unless they are finely chipped or shredded. Chop your garden trimmings with a shovel or machete or run them through a chipping machine or lawnmower to speed their decomposition. Aim for particle sizes ranging from 1/8 to 2 inches average diameter.

The compost pile will require carbon- and nitrogen-rich materials for efficient decomposition. Micro­organisms use carbon for both energy and growth, while nitrogen is essential for growth and reproduction. Carbon is found in dry, brown materials, such as leaves, chipped woody brush, sawdust and straw. Nitrogen is most abundant in fresh, green yard and garden trimmings, vegetable scraps and livestock manures. The proper compost mixture contains approximately 2 parts carbon-rich materials to 1 part nitrogen-rich material.

Too little carbon leada to the production of excess ammonia and unpleasant odors. Too little nitrogen limits the growth of microorganisms and the composting process slows dramatically.

Step 4 – Aerating (the pitchfork is your friend)

Aerobic composting consumes large amounts of oxygen, particularly during the initial stages. If the supply of oxygen is limited, the composting process may turn anaerobic, which is a much slower and more odorous process. Replenish the oxygen levels within the piles by lifting and turning the materials with a pitch-fork. Aim to put the outside, drier materials in the center of newly turned piles. Turning a pile weekly can produce compost in one to two months with the right combination of materials and moisture level; monthly turning will produce compost in four to six months. Without turning, composting may take six months to two years. Aeration is generally the main factor affecting the time necessary to produce finished compost.

Step 5 – Keeping the pile moist

As a rule of thumb, the materials are too wet if water can be squeezed out of a handful of compost and too dry if the handful does not feel moist to the touch. If the compost pile is too dry, the process slows down. If the compost pile is too wet water will displace much of the air in the pore spaces of the composting mater­ials. This limits air movement and leads to anaerobic conditions. Mois­ture content generally decreases as composting proceeds; you may need to water the compost occasionally.

Step 6 – Keeping the pile at the proper temperature

Composting will essentially take place within two temperature ranges known as mesophilic (50-105 degrees F.) and thermophilic (over 105 degrees F.). Keeping temperatures at 110-150 degrees destroys more pathogens, weed seeds and fly larvae in the composting materials.

If the temperature of your compost pile is in the mesophilic range, mix the pile more frequently. If the temperature still does not reach the thermophilic range, review the steps described above: Is one or more of the essential factors is limiting the composting process?

Finished compost is dark, crumbly, and has an earthy and non-offensive odor. Pile temperature in finished compost may still be slightly higher than ambient air temperature.

Step 7 – Curing

Curing refers to leaving finished compost in a pile undisturbed for up to one month to allow any final chemical and decompostion reactions to occur and stabilize the compost. Improperly or incompletely composted materials may release ammonia and other gases, or continue to heat upon application to soil, damaging plants. Curing ensures that the composting process is indeed complete and that these potential problems are minimized. View the curing phase as extra insurance against problems arising from using compost.

This article was originally published on March 29, 2013.