Science activity
Composting Science
Discover how food scraps turn into dirt! Start a compost jar and watch banana peels and leaves slowly change over time. Nature's recycling is amazing!
Materials and setup
- clear jars with lids
- food scraps (banana peel, apple core)
- dead leaves
- soil
- water spray bottle
- paper
- markers
- kitchen scale (optional)
How this changes by age
Pre-K (ages 3–4)
Discover how food scraps turn into dirt! Start a compost jar and watch banana peels and leaves slowly change over time. Nature's recycling is amazing!
Steps
- Collect food scraps together: banana peel, apple core, carrot top, dead leaves, and grass clippings.
- Put the scraps in a large clear jar with some soil and a sprinkle of water.
- Poke a few small holes in the lid (parent does this) so air can get in.
- Put the jar in a warm spot. Every few days, look at the scraps. 'Are they changing? Getting smaller? Changing color?'
- After 2-3 weeks, compare to the beginning: 'The tiny helpers in the soil — bacteria and bugs — are eating the scraps and turning them into rich soil!'
- Tell a grown-up one thing that surprised you.
Learning objectives
- Observe that food scraps decompose and change over time
- Understand that decomposition is a natural recycling process
- Practice long-term observation of a slow natural process
Kindergarten (ages 5–6)
Set up a compost experiment: test what decomposes and what doesn't. Compare food scraps, paper, and plastic over several weeks. Learn about decomposers and why composting helps the planet.
Steps
- Set up 4 clear jars with damp soil in each.
- In jar 1, bury a banana peel. In jar 2, bury a piece of paper. In jar 3, bury a piece of plastic. In jar 4, bury an apple core.
- Label each jar and place them all in the same warm spot.
- Check every 3-4 days for 3 weeks. Draw what each item looks like. Rate decomposition: 'Not changed / A little changed / Mostly gone.'
- Compare results: 'The food scraps and paper broke down, but the plastic didn't change at all!'
- Discuss: 'Tiny creatures called decomposers eat natural materials. They can't eat plastic. That is why plastic trash is such a big problem!'
- Tell a grown-up one thing that surprised you.
Learning objectives
- Compare decomposition rates of organic and non-organic materials
- Understand that decomposers break down natural materials but not plastics
- Connect composting to reducing waste and helping the environment
Early elementary (ages 6–8)
Investigate decomposition scientifically: test variables that affect composting speed, learn about the organisms that drive decomposition, and design an optimized compost system.
Steps
- Research decomposition: bacteria, fungi, earthworms, and insects break down organic matter. They need moisture, air, warmth, and a balance of nitrogen-rich (greens: food scraps) and carbon-rich (browns: leaves, paper) materials.
- Set up a variable test: make 4 compost bags with identical food scraps. Vary ONE condition: (1) moist + warm (control), (2) dry + warm, (3) moist + cold (fridge), (4) moist + no air (sealed tight).
- Observe weekly for 4 weeks. Rate decomposition (1-5 scale), note color changes, smell (1-5), and visible organisms.
- Research the composting food web: bacteria start the process, then fungi, then larger organisms (mites, springtails, worms). Draw a decomposition food web.
- Design an optimized compost bin for your household: specify size, materials, green-to-brown ratio, moisture plan, and turning schedule. Explain why each choice helps decomposition.
- Write a report: explain the science of decomposition, present your variable test results, and include your compost bin design with reasoning.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Identify the conditions that speed up or slow down decomposition
- Describe the organisms involved in decomposition and their roles
- Design an optimized composting system based on experimental evidence
Upper elementary (ages 8–10)
Conduct a comprehensive study of decomposition and nutrient cycling: measure decomposition rates quantitatively, explore the carbon and nitrogen cycles, analyze composting chemistry, and evaluate composting as a climate solution.
Steps
- Research nutrient cycling: decomposition is essential for the carbon cycle and nitrogen cycle. Draw both cycles showing how composting fits in (organic matter to CO2, nitrogen fixation, nutrient return to soil).
- Design a quantitative decomposition experiment: weigh identical food scraps before burial. After 2, 4, and 6 weeks, carefully excavate and reweigh. Calculate percentage mass lost over time. Graph the decomposition curve.
- Test compost quality: grow plants in regular soil vs. soil mixed with finished compost. Measure growth differences over 3 weeks. This demonstrates nutrient return to the ecosystem.
- Research composting chemistry: what is the ideal carbon-to-nitrogen ratio (C:N)? Why does compost heat up (thermophilic decomposition)? What is the difference between aerobic and anaerobic decomposition?
- Analyze composting as a climate solution: research how much food waste goes to landfills, how landfill decomposition produces methane (a potent greenhouse gas), and how composting reduces these emissions. Calculate your household's food waste impact.
- Write a scientific paper: cover nutrient cycling, your decomposition data and plant growth comparison, composting chemistry, and a cost-benefit analysis of composting as a climate strategy.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Measure decomposition rates quantitatively and create decomposition curves
- Explain carbon and nitrogen cycling through decomposition processes
- Evaluate composting as a climate solution with data-driven analysis
Safety and evidence note
Read the full activity before beginning. An adult should supervise tools, heat, food, outdoor work, movement, and experiments as appropriate. Completion records that the activity was done; the child’s explanation, work sample, photo, or demonstration is stronger evidence of learning than a completion check alone.
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