Composting involves a complex food web in which familiar soil invertebrates such as millipedes, sow bugs, snails, and slugs help shred organic matter into smaller pieces. This, in turn, assists microorganisms such as fungi and bacteria to do their job of further breaking down the material. The cycle continues as the invertebrates feed on the microorganisms. All of the above decomposers help release nutrients that eventually mix with the moisture in the soil and are taken up by the roots of plants. See if your kids can guess how many living things are in one handful of compost: between 5-10 billion!!

Decomposing organisms need 4 key elements to thrive:
nitrogen - acts like a protein source for microbes (grass clippings and livestock manure)
carbon - source of energy for microbes (dried leaves and twigs)
moisture - a compost pile or bin should be kept as moist as a wrung-out sponge
oxygen.... essential for microbes to live and do their work (more oxygen = quicker decomposition

Two of the most common types of composting are backyard composting and vermicomposting. Backyard composting simply requires piling leaves and grass clippings on the ground or in a bin or can including all non-meat and dairy kitchen waste (e.g. egg shells, coffee grounds, dryer lint). This type of decomposition is slow but requires little maintenance. Vermicomposting enlists the aid of red worms to speed up the composting process.

The concept of composting has been around for a long time. Ancient Romans were known to plow composted animal manure and vegetation into their fields to create rich soil. George Washington and Thomas Jefferson were also strong believers in the values of composting.

You’ll need:
To begin your discussion on decomposition and composting, you might want to read, The Tenth Good Thing About Barney by Judith Viorst or simply begin by asking students if they have ever seen anything in nature decomposing (such as fallen leaves).

Use the Treeture, Humus, as a guide, icon or symbol to help animate and enhance your composting lesson. Humus is a Dirt Dumper who enjoys inviting his friends to his composting parties. He loves eating nature’s garbage (fallen leaves, twigs, vegetation) and leaving a trail of leftovers to enrich the soil wherever he goes. Brainstorm what factors in nature might help Humus with this decomposition of nature’s garbage. Students may come up with examples such as heat since leaves are often intact over the winter, darkness since this promotes fungus growth, or small organisms in soil.

Discuss what composting is and ask the question, "Why would composting be beneficial?" Students should give answers that include: less waste in landfills where trash cannot break down, makes fertile soil for more things to grow, easy, not expensive. Ask students what biodegradable materials they could compost at school in order to create less waste. Keep a running list. Have students complete the worksheet about what is okay and not okay to compost in the Stomper section of the Treeture website.

Invite Humus to your classroom to create your own composting party. Half fill plastic milk jug or a sealable plastic bag with small air holes in the top half with soil from school grounds. Use saran wrap with small air holes in the top to cover your compost bin if you are worried about odor, however, compost bins usually do not have an unpleasant odor unless the ingredients are out of balance. Instead, they should have no odor or smell like a forest after a rain. Add biodegradable materials as they are collected. Keep the soil as moist as a wrung-out sponge and assign students to turn the soil once a week to mix it up and allow for more oxygen or allow students to set up their compost bins using the factors they brainstormed earlier that they felt promote decomposition. Use the composting form to chart the progress of your composting materials.

The rich compost soil, humus, can be used to fertilize plants and trees growing in or around your school, for new flower gardens and trees being planted. You could also set up several composting experiments to observe the rate of decomposition. Use the same ingredients in each compost bin as your control and change the variables such as amount of light, amount of water, amount of turning of soil, etc.

Visit Stomper or Mud Meister for more ideas and resources.

Extension:

• Literature connections might include reading, Jack and the Meanstalk by Brian and Rebecca Wildsmith or June 29, 1999 by .David Wiesner. Have students write their own stories about a special tree growing formula they have invented and tell about the adventure that takes place when the experiment goes awry.

• Plan a party for Humus. Think about who would be on the guest list, what food might be served, and what activities might occur.

Suggested Readings:

• Let It Rot by Stu Campbell
• Earthworms, Dirt, and Rotten Leaves by Molly McLaughlin
• Cornell University’s Composting in School at http://compost.css.cornell.edu/schools.html
• Worms Eat Our Garbage:Classroom Activities for a Better Environment by Mary Applehof, Flower Press, 10332 Shaver Rd., Kalamazoo, MI 49002
• The Tenth Good Thing About Barney by Judith Viorst
• June 29, 1999 by David Wiesner
• The Plant That Ate Dirty Socks by Nancy McArthur