Like HowStuffWorks on Facebook!

How Composting Works


Care and Feeding

Add new layers of composting material to the top along with fresh soil. Water the compost bin regularly to keep the compost moist. Turn the compost everyday or every other day to ensure an adequate supply of oxygen. With some bins, you can avoid turning the compost by inserting perforated PVC pipes into the bins to introduce a regular air supply.

Worm Composting
Worms can reduce composting times by as much as 50 percent. You can seed your compost pile with earthworms or buy special composting worms. You can also set up a worm box outside the house to process kitchen waste and meat scraps. See the Lots More Information section for more on worm composting.

As you add new layers and turn the compost, you will be mixing new layers of intact trash with partially decomposed layers. The partially and nearly finished material will settle to the bottom because the particles are smaller. The finished compost will come out the bottom of the bin. In three-bin systems, you add intact trash to the first bin and actively transfer partially and finished compost to the second and third bins.

Here are some signs that your compost pile is working properly:

  • It does not smell bad. It should have a sweet, earthy smell, like peat moss.
  • It is warm. The microorganisms are "cooking away" and you may even see some steam rising from the pile, especially on a cool morning.
  • You may see some gas bubbles in the pile, because carbon dioxide is being released as the microorganisms do their work.

Collect the Finished Compost
The finished compost will collect at the bottom of the bin in a single bin system or at the third bin in a three-bin system. There is no strict definition of when the compost is done. Basically, if you think it's done, it's done. Here are some parameters that you can use to judge this:

  • Temperature - After you turn the pile, measure the temperature. If it is below 100 F (38 C), then it is probably done.
  • Appearance - Does the material look at least 50 percent decomposed? Can you recognize anything in it as the trash you put in?
  • Size - Has the volume of the compost reduced by 50 to 75 percent?
  • Color - Is it dark brown or black?
  • Texture - Is it smooth or crumbly?
  • Smell - Does it smell earthy like soil?

Once your compost is done, it is ready to use. Finished composts can do the following:

  • Improve the soil structure in your garden or yard
  • Increase the activity of soil microbes
  • Enhance the nutrients of your soil
  • Improve the chemistry of your soil, particularly the degree of acidity (pH)
  • Insulate the changes in soil temperature around plants and trees
  • Improve insect/disease resistance in your garden plants and trees

Most home composters use their finished product around their own home, in their trees or gardens. Some home composters sell their finished compost to local nurseries or other family gardeners.


More to Explore