How things compost

How Things Compost

Grade 3 Earth and Space Science-Exploring Soils (ES)

Outcomes:

  • ES3.1  Investigate the characteristics, including soil composition and ability to absorb water, of different types of soils in their environment.
  • ES3.2 Analyze the interdependence between soil and living things, including the importance of soil for individuals, society, and all components of the environment.

Teacher’s Note: In this activity students observe the ongoing process of decomposition.  It could go on several weeks, but should continue over at least 5 weeks.  If started in early spring, partially finished compost could be moved to an outside composter or into a school garden.

Day 1

Materials

Carbon/Brown materials- Dry leaves, a bit of straw, paper towel, dead plant material, etc.

Nitrogen/Green materials- grass clippings, fruit or vegetable scraps, etc.

  • Clear jar, like a large pickle jar (1 for each group).
  • Cloth or cheesecloth coverings (fasten with elastic; keeps bugs at bay, and allows air flow).
  • Garbage bag or 1 large piece of plastic.

Micro-organisms/Bacteria- Rich garden soil or potting soil for each group

Other Items- Experimental items (aluminum foil, twigs, milk cartons, cardboard, plastic, etc.)

Instructional Procedures

  1. Show the short video from http://videos.howstuffworks.com (1:48) Use this video as a springboard of discussion of what students know about composting.
  2. Discuss with students what a good compost mix needs:
    • “Brown” material (carbon-rich).  Brown materials include things like fallen leaves, straw, newspaper, sawdust or any other dead, dried plant material
    • “Green” material (nitrogen-rich).  Green materials include things like grass clippings, fruit or vegetable scraps, coffee grounds, garden waste and other fresh plant materials. 
    • Moisture.
    • A source of micro-organisms and bacteria (soil)
    • Warmth.
  3. Brainstorm a list of things that students can easily obtain to be included in a classroom compost.  Ask students to bring items to be composted for next class, or collect school lunch waste.  Encourage and allow students to bring some non-conventional and non-food items – such as newsprint, paper towels, coffee grounds, etc. 

    * Teacher Note * Students may ask about meat, dairy and animal waste.  These items are compostable but are not encouraged for household composting as they may cause unpleasant odors and attract vermin.

  4. Make one sample compost jar with the whole class.
    • In a clear jar place a layer of rich soil.
    • Add a layer of compostable material, such as grass clippings or leaves.  The soil should be moist, or add a small amount of water.  Label the outside of the jar with the contents and date.
    • Add at least one more layer of soil.  You could add additional layers of compost material if you wish.
    • Make note of what the mixture looks and smells like.
    • Cover and put the jar in an out-of-the-way place, so it can “stew”.  It should be kept inside so that it doesn’t freeze.
    • Wash hands.

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Day 2

  1. Bring out the sample jar.  Look at the compost mixture and observe any changes in appearance or odor, also to be recorded.  Discuss changes or lack thereof. Why? Check the moisture level; if it seems dry, add a bit more water.  Cover and put away again.
  2. Divide students into small groups.
  3. Have the students assemble their own compost jars, using the soil and whatever they brought to be composted.  Layer the soil with compostable materials (must be small enough to fit into jar).  Each layer of compostable material should be separated by a soil layer (i.e. a layer of soil, layer of banana peel, layer of soil, layer of leaves, layer of soil, etc.).  Try to get the compost materials up against the side of the jar so they can be observed.  They should also add some of the extra items (twigs, cloth, aluminum can, etc.).  Label the jars with the contents, date and group name.  Wash hands.
  4. Students should make their observations and complete The Compost Observation Recording Sheet for day 1.
  5. Discuss the students’ predictions. Which items will decompose first?
  6. Cover the compost and put away.

Day 3 (one week later)

  1. Have each group observe and record appearance and odors on the Compost Observation Recording Sheet - 1 Week Later.
  2. Students may want to change their predictions.  Changes should be recorded.
  3. Cover and put away.
  4. Lead a class discussion in what the students are finding.
    • What surprises them?
    • What do they expect to observe in 4 weeks?

Day 4 (one month later)

  1. Have each group observe and record appearance and odors on the Compost Observation Recording Sheet – 1 Month Later.
  2. Revisit predictions and note discrepancies.
  3. You may choose to continue the experiment longer, but the base of it is complete.  Lay out a large piece of plastic or the garbage bag, and spread out the contents of the compost jars.  Have students remove large pieces of wood and paper, and also any metal, glass or plastic; then the material that is left can be put in the school compost bin or buried in the garden where decomposition can continue.  Remember to clean the jars for reuse or recycling.
  4. Class discussion:
    • Have each group share their findings on what decomposed the quickest, the slowest and not at all.
    • Groups could also share their predictions and how they differed from their findings.
    • Discuss any surprising findings.

Additional Resources

Additional Inquiry:

Vocabulary List

  • compost
  • decomposition
  • decompose
  • carbon
  • nitrogen
  • soil
  • micro-organisms
  • bacteria
  • prediction

Printable PDF version including all worksheets

 

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How things compost

 Printable PDF version including worksheets
 
Recycle Saskatchewan is a joint project of SARCAN Recycling, the Sask. Waste Electronic Equipment Program, the Sask. Association for Resource Recovery Corporation, the Sask. Scrap Tire Corporation, the Sask. Paint Recycling Program and the Sask. Waste Reduction Council.