Composting 101

Susan Perry
Colorado State University Extension Master Gardener in Larimer County
April 28, 2012

Spring is a great time to begin composting for several reasons. First, you can begin gathering the ingredients for the compost pile during spring cleanup. In addition, homemade compost is a great addition to amend our soils and add some nutrients. Also, the warming weather makes it easier to venture outside to consistently add to, moisten, and turn the pile, as well as to enable the pile to warm up. Finally, spring is a great time to begin the ultimate recycling: rather than putting yard waste and vegetative kitchen scraps into your garbage and landfill, you can return them to the landscape in a productive way. You will be surprised at how much smaller your trash bag is every week.

A compost pile consists of four elements: browns, greens, water and air.

  • Browns: dried leaves and grasses, and other dried yard waste
  • Greens: fresh kitchen vegetable and fruit scraps, coffee and tea grounds, egg shells, old fruits, vegetables and stale bread
  • Water
  • Air

Generally, the pile should consist of alternating six to eight inch layers of shredded browns and greens. Shredding the components to one-half to one inch in size will speed up the composting process (although over-shredding will have the opposite effect). Adequate moisture and regularly turning the pile to add air every three to five days will also speed up the decomposition process. Remember, un-shredded browns left alone in a pile outside will eventually decompose, but the addition of greens, regular turning (air), moisture and moderate shredding of components are simply ways of speeding up the natural decomposition process.

Moisten each layer as you add it; the mixture should be the approximate wetness of a wrung-out sponge. If you add too much water, the pile will start to smell; too little water will result in little decomposition, a dry outside, an ashy interior and possibly the death of the microbes necessary for the decomposition process. The best way to learn is through trial and error, remembering all “errors” can be corrected. If you’ve added too much water, turn the pile more often to dry it out and mix in more shredded browns. If the pile is too dry, be more generous with the greens and the water as you turn and layer the pile, and consider covering it on dry days with a tarp to keep moisture in.

No meats, oils, fats, human or pet urine or feces, whole eggs, bones or dairy should be added as these can attract rodents. Try to avoid cottonwood and oak leaves, which contain high tannins, large twigs and branches and resinous wood scraps such as pine, juniper and spruce. Grass clippings can be used in limited quantities if care is taken to prevent large clumps and matting, but research shows clippings are best left on the yard to add nutrients.

Because temperatures vary in different areas of the compost pile, it is best to avoid weeds and diseased plants, as they may not be killed during the composting process. Although traditional composting recommends the addition of soil or manure as a way of adding microbes to the pile, research has shown this only adds unnecessary weight and bulk to the pile, and can become a source of pathogens. And while black and white newspaper was also considered a traditional component, modern recycling is a more effective method of disposing of newspaper than composting. Finally, it is best to avoid adding any yard waste that was treated with pesticides or herbicides.

Locate the pile in an area that has partial or dappled shade and is somewhat protected from drying winds. Other considerations are proximity to regular water, appearance and local covenants, space to move around as you turn or aerate the pile, and convenience for moving components in and finished compost out of the area. Regardless of where you locate your pile, seek a balance of natural heat and moisture to prevent drying from sun and wind.

Many people build their own compost bins, while others purchase them. In either case, once you have created a pile of adequate volume (approximately 3’ x 3’ x 3’), it should heat up within several days. Slightly smaller volume piles can also be effective, given the correct conditions and management. Within four to six weeks, your pile should stop showing signs of activity. You should allow it to cure for another two to four weeks before using it as a soil amendment or a mulch/top-dressing. If your cured compost has large particles, they can be sifted out before use.

For additional information on composting, consult CSU Factsheet #7.212 from


The author has received training through Colorado State University Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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Updated Tuesday, July 22, 2014