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R is for Rot


To investigate how decomposers turn garbage into valuable compost and to demonstrate the role of decomposers in an ecosystem.


Life Science, Grades 58, Populations and Ecosystems, Decomposers, primarily bacteria

and fungi, are consumers that use waste materials and dead organisms for food.


80 minutes (for construction of composter, plus several weeks of observations)


  • plastic garbage can with lid or a large box with lid

  • organic soil

  • yard trimmings (grass clippings, decaying leaves, straw, or hay), food wastes (vegetable and fruit peelings, used tea bags and coffee grounds, nutshells)

  • water (optional)

  • earthworms (optional)

  • pitchfork

  • student journals


Have students compare how quickly bread with preservatives rots compared to bread made with- out preservatives. Have them set up an experi- ment, complete with controls, that compares growth rates of mold on moist slices of bread placed in resealable plastic bags and left in a cool dark place. Encourage them to present their findings in a written report.


  • If you have the time and space to construct a class composter on school grounds, follow the directions as described. If you are not able to construct a composter, use the information provided to discuss with students how one is constructed then have them design one on paper, label the parts, and describe the decomposition process occurring within. Alternately, you can have students do research themselves and use the information provided as a reference. Students can create a detailed diagram of a composter and perhaps bring it home to share with their families.

  • Ask students to list the things they throw out in the garbage every week. (Students may name food scraps, paper products, plastic, etc.) Tell students that about 20 percent of the garbage thrown away by people in the Unites States is organic, meaning once alive.Review with students what they learned about what happens to living things that have died in R is for Rot.(They are broken down by decomposers, like bacteria and fungi, into materials that can be used again by plants.)

  • Ask students if they know what a composter is. Most will know that a composter (or compost pile) is a collection of organic material that, when left to decomposers, produces rich soil that can be used in the garden.

  • Brainstorm a list of materials students think could go into a composter. (Yard trimmings, food wastessee materials list.) Also discuss things that should not go in the composter. (Meat and animal bones as they attract dogs and cats.) Then discuss how the pile should be set up. (It needs to be contained in something, maybe a box or can; it should contain some soil to supply the right decomposing microorganisms; it needs air for the microorganisms to live.) Discuss the best way to arrange these components in a composter. (They should be arranged in thin, loose layers so air can circulate.)

  • If feasible, construct a composter with the class. You may choose to bring in the yard and food scraps yourself, or solicit student partici- pation. You might consider involving your own cafeteria and grounds department in collecting the organic wastes.

  • Poke holes all over the garbage can and its lid to allow air to circu- late. The holes should be about 1/4 inch in diameter. Then add thin layers of organic soil, shredded yard waste, and shredded food waste. (Shredding helps speed up the decomposition process.) If the material seems dry, add a small amount of water. You may choose to put some earthworms in the can as well. Earthworms are considered shredders,not decomposers. But they play a very important role as they shred waste materials into smaller pieces that bacteria and fungi can then decompose more quickly.

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