Children in the preschool years (two and a half to five years old) are learning all about the world around them and how everything works, making this the ideal for them to learn the benefits and basic science of decomposition. A compost pile in the classroom allows young students to learn through hands-on activities, have fun and get dirty along the way. Begin composting in the fall to use the soil in the spring for a classroom garden, or even to just add soil around the flowers in the front of the school. You can also use it to grow seeds or plant Mother’s Day flowers in cups.
Obtain an aquarium (or terrarium), which is durable to hold the compost and easier to see what is going on inside. You do not need a lid. An aquarium that is 10 or more gallons will work for a preschool compost project. Set it in an area out of direct sunlight and at room temperature, according to the Department of Natural Resources. Microorganisms working to decompose the organic material cannot survive in extreme temperatures, so do not place the tank in the sun or next to a heating source, such as a radiator.
Give each child a quart-sized plastic storage freezer bag to collect garden waste and food scraps, such as grass clippings, leaves, nut shells and carrot peels. They should not collect meats, fats, oils or dairy products since they will smell and attract bugs and/or slow down decomposition. Write examples for the parents of what organic matter is acceptable and not acceptable to collect on the bag or on a separate sheet of paper.
Chop or tear apart the organic matter in front of the students. They can help by ripping and crushing things like leaves and nut shells. Teach them that the smaller pieces will decompose quicker than the bigger pieces. Do not chop up some pieces and add them to the compost pile for the students to see how these are slower to decompose, if desired. Add some grass clippings, which will add nitrogen to the compost to help speed up decomposition.
Have students fill the aquarium. Lay approximately one inch of soil (such as commercial top soil), two inches of organic matter, a thin layer of grass clippings and a sprinkle of water inside the aquarium. Repeat these layers until the aquarium is filled about three inches from the top. Add one inch of soil on top and water the compost pile with enough water to get all the contents moist but not soggy. Add about 12 to 24 earthworms to the compost pile. Students can collect these earthworms if desired at home or on school property (after a rain is easier) or you can buy them at a garden center.
Allow students to turn over the pile once a week with a trowel and add water as necessary to keep the pile slightly moist. You can add and work in more organic matter to the compost pile as it decomposes. If your compost pile has a bad odor, it is probably too moist. Add some wood chips or newspaper to help remove some of the moisture.
Make observations. Students can keep a journal, drawing what they see going on with the compost pile, perhaps every week before the pile gets turned. The teacher can write a caption for the children under each picture. Teacher or students can share their journals throughout the year with the entire class.