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Composting Methods

4.3 based on 3 ratings

Updated on Sep 11, 2013

Gardeners appreciate the value of compost. Called “gardener’s gold,” it adds valuable nutrients to the soil. Many gardeners make their own compost, but others often fail because they put their food scraps and lawn clippings in a pile, which fails to decompose. The bacteria responsible for decomposition of organic matter require very particular conditions. Students will investigate the effect of heat, light and moisture on decomposition and determine which composting methods favor these bacteria.


Which composting methods break down organic matter the best?


  • 12 one-gallon plastic bags
  • Two pounds of carrots
  • An accurate scale either triple beam, or electric, that measures 0.1 gram units accurately
  • Rags
  • Five gallons of high quality potting soil


  1. Cut carrots into 12 1 to 2 inch pieces.
  2. Label four 1-gallon plastic bags “temperature,” “moisture,” “oxygen,” and “light.”
  3. Create a data sheet or spread sheet with five columns labeled “date,” “temperature,” “moisture,” “oxygen,” and “light.”
  4. Fill four 1-gallon plastic bags with equal potting soil. The bags should all be full.
  5. Take three pieces of carrot and weigh them. Enter the total weight of the three carrots into the column headed “temperature.” Put the carrots into the corresponding plastic bag.
  6. Repeat Step #4 three times, using the bags and columns labeled “moisture,” “oxygen,” and “light.”
  7. Place the bag labeled “temperature” into the freezer.
  8. Lightly mist the contents of the large labeled “moisture” and seal. Store in a room temperature room.
  9. Thoroughly soak the potting soil and carrots in the bag labeled “oxygen.” Squeeze all the air out of the bag before sealing.
  10. Wrap the bag labeled “light” in towels so that the contents are not exposed to light.
  11. Every day, take the carrots out of the bag and remove as little of the potting soil as possible. Weigh the carrots. Try to keep as much air out of the bag labeled “oxygen” as possible. Repeat this step every day for four to six weeks. Don’t be alarmed if some of your data appears inconsistent or unexpected as some of the weights may increase instead of decrease. Consider what factors are causing the increase.
  12. After significant decomposition has taken place, calculate the total weight loss. What percent of the total weight has been lost? Which condition is associated with the greatest loss?
Cy Ashley Webb is a science writer. In addition to having worked as a bench scientist and patent agent, she judges science fairs in the San Francisco bay area. She loves working with kids and inspiring them to explore the world through science.