THEME: Organic waste can be recycled (composted) and used to enrich soil.

GOAL: Students will learn about recycling organic wastes through composting.

METHOD: Building a model compost pile


SKILLS: Classifying, inferring, observing, predicting

MATERIALS: Aquarium; organic wastes: soil (NOT potting soil); thermometer; trowel or large spoon; 1 to 2 dozen red earthworms

TIME: 1 hour to assemble, up to 1 year for observation


Composting is the oldest form of recycling. It is based on the scientific principle that nothing ever really dies, but just changes shape and takes on new forms. When a leaf falls and begins to decompose, it is broken down by time, weather, insects, and worms into the original materials from which it was made. The same is true for waste we throw away every day, such as grass clippings, banana peels, egg shells, and apple cores. These materials can be set aside for use as fertilizers in gardens and farms

Compost is formed through the action of certain microbes that proliferate when mixed organic refuse receives sufficient air and water. These bacteria, which generate a temperature of 150 degrees, literally cook the wastes. The finished product, called "compost" or "humus," is an excellent fertilizer and looks just like soil. It is high in carbon and nitrogen, which are important sources of food for plants and vegetables. In addition to being clean, safe, and thrifty, composting can significantly reduce the volume of solid waste generated by a household.

-Oscar's Options 

Getting Started

Can food scraps, leaves, and grass clippings be recycled?


  1. Have the students bring in a variety of organic wastes such as green grass clippings, sawdust, wood ash, leaves, and kitchen food scraps. (Avoid meat scraps, dairy products, fats, and oils, which inhibit decomposition, cause odors, and can attract pests.) Tear or chop the materials into small pieces, leaving a few larger pieces of each type of waste for comparing rates of decomposition. Ask the students if they think there will be a difference.
  1. Begin to fill the aquarium, alternating layers of the materials as follows (amounts are approximate): 1 inch of soil; 2 inches of dry, carbon rich, organic waste (i.e., leaves); 1 inch of green grass clippings; and sprinkle of water. Repeat several times.
  1. Cover the last layer with a half inch of soil and water the pile so it is moist, but not soggy-like a damp sponge.
  1. Have the students add the earthworms and observe their behavior.
  1. Place the compost pile where it will be at room temperature (but not in direct sunlight). Once a week, have a student test the temperature of the pile and vigorously mix the pile to aerate it. For consistency, take the temperature at the same location, depth, and time each week. Make a temperature graph and have each student enter his or her reading.
  1. As the class starts to see changes in the pile, discuss the process of composting. How does it reduce the amount of waste thrown out? What happens to organic wastes that end up in the landfill? Is the landfill a gigantic natural compost pile, or are there problems with placing large amounts of organic material in landfills?


  1. Have the children write and illustrate a story that explains what they have learned about composting. Where applicable, encourage them to construct a compost pile at home, where they can use the finished compost on the family garden or flower beds.
  1. Have the class begin a school garden or "adopt" a particular flower bed. Have them add the compost they made and plant some flowers or vegetables.

Source: Adapted from Wisconsin, Recycling Study Guide