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How Composting Works

Making Compost

Photo courtesy Karim Nice
Where do you want your compost pile?

To make compost, you must do the following:

  • Choose a site for the compost pile.
  • Choose a structure.
  • Add the ingredients.
  • Care for and feed the compost pile.
  • Collect the finished compost for use.

Choose a Site
Where you want your compost pile is an important question. You want to be able to compost discretely away from your house, but not so far away that you may not want to go out and attend to it. Also, you do not want it so close to the boundaries of your property that your neighbors might complain. Part of the answer may be dictated by local housing ordinances or homeowner organization rules that may specify where a compost pile can be located. Other factors to consider include the following:

  • Downwind from your house - Even a well-managed compost pile may occasionally emit unpleasant odors.
  • Wind - Although wind provides air, too much wind can dry and/or scatter the material.
  • Sunlight - Sunlight can help warm the compost pile in the winter, but too much sunlight can dry it out. If the pile is located by a large deciduous tree, you will have cool shade in the summer and sunlight in the winter.
  • Drainage - You want good drainage so that water will not accumulate by the pile.
  • Surface - Bare earth is better than concrete. Make sure to give yourself a sufficient work area around the pile (6 to 8 ft, or about 2 m).

Compost structures come in many shapes.

Choose a Structure
Compost structures can be as simple as a heap where you just pile all of the ingredients and let nature take its course -- this is passive composting. Passive composting is less efficient and slower than active composting, in which you manage the compost process on a daily basis.

You can also build more complicated compost bins out of chicken wire, wood or concrete blocks. They can be simple, one-compartment structures in which you add new materials to the top, turn the compost frequently and collect the finished compost from the bottom.

Photo courtesy Karim Nice
home composting unit

They can also be multi-compartment (three-bin) structures in which you add new material to one bin, transfer partially-completed compost to the middle bin and move finished compost to the final bin. There should be some covering on the top of the bin to minimize excess rainwater and reduce scattering from the wind. Many varieties of compost bins are available commercially.

The choice depends entirely on the effort and expense that you wish to devote to the project, as well as the amount of compost that you wish to make. Also, local ordinances may dictate what kind of bin you can use.

Add the Ingredients
You can compost the following materials easily:

Composting Meat & Dairy
Meat and dairy products are high in fat. They will cause an unpleasant odor if added to a passive pile or poorly-managed active compost pile. For a hot, well-turned compost pile, meat and dairy wastes are not a problem. However, it is better to run the wastes through a blender or food processor to reduce their size and speed their decomposition.
  • Kitchen waste - best to chop up or grind the wastes so that they can be broken down faster
    • Fruit and vegetable wastes - peels, skins, seeds, leaves
    • Egg shells
    • Coffee grounds (including paper filters), tea bags, used paper napkins
    • Corncobs - should be shredded to make them break down quickly
    • Meat/dairy products - see sidebar
  • Yard waste
    • Grass clippings - Some grass is okay, but too much will add excess nitrogen to the compost pile and make it smell bad. It may be best to use a mulching lawn mower for your grass.
    • Leaves
    • Pine needles
    • Weeds
    • Woody materials (branches, twigs)
    • Straw or hay
  • Newspaper
  • Seaweed, kelp or marsh grass hay - If you live by the ocean and it is legal to harvest these, they are excellent, nutrient-rich materials. Rinse or soak them thoroughly in fresh water to remove excess salt before adding them to your compost pile.
  • Sawdust - This is an excellent source of carbon.

Photo courtesy Karim Nice
Kitchen and yard waste in a compost bin

The following materials SHOULD NOT BE COMPOSTED:

  • Human waste or pet litter - They carry diseases and parasites, as well as cause an unpleasant odor.
  • Diseased garden plants - They can infect the compost pile and influence the finished product.
  • Invasive weeds - Spores and seeds of invasive weeds (buttercups, morning glory, quack grass) can survive the decomposition process and spread to your desired plants when you use the finished compost.
  • Charcoal ashes - They are toxic to the soil microorganisms.  
  • Pesticide-treated plant material - These are harmful to the compost foodweb organisms, and pesticides may survive into the finished compost.

Cover the composting materials with plenty of soil in the compost bin. Some sources say that it is best to arrange carbon-rich and nitrogen-rich materials in alternating layers. Add water to moisten the compost, but do not soak it. Turn the compost with a shovel or compost fork to mix it and provide plenty of air.