STEAM Kids: Compost in a Cup


For the “Compost in a Cup” experiment, we are going to make a mini composting bin in a cup to show the composting process and how composting can reduce food waste and help the environment.

Ingredients and supplies:

• 16 oz. cup with holes in the bottom

• Pair of gloves

• Large bowl

• Organic compostable items – Leaves, grass clippings, vegetable scraps, fruit scraps, coffee grinds, etc.

• 1/4 cup soil or dirt

• 1-2 teaspoons of water

• Piece of plastic wrap

• Rubber band

• Large plastic spoon


Before beginning this experiment, you will need to collect the organic items you plan on composting. There are many different materials you can add to your compost cup. (See the list of what to include, above) Things that come from plants or trees, orange peels, excess fruit, eggshells, etc are good to include. Things you do not want to include are meat, dairy products, and seafood. Once you have collected your organic items, make sure they are torn or chopped up into small pieces and place them in a large bowl, add 1/4 cup of dirt and 1-2 teaspoons of water, and mix.

Next, take your 16 oz. cup with holes in the bottom, and a pair of gloves. Using the large plastic spoon, take 2 scoops from your bowl and place them into your cup. Now, take your piece of plastic wrap and place it on top of your cup. Secure it around the rim of the cup with the rubber band. Make sure the plastic wrap is nice and tight on the cup and the rubber band is secure.

Compost piles need sun, shade, water, and movement so put your cup in a window that gets a good amount of sun or outside in an area that has exposure to the sun for part of the day. Periodically add 1 teaspoon of water to your cup and give the contents a little “shake”. If placed outside, rainwater and a little “shake” will do the trick! The water and movement will assist with the composting process.

The area in which you choose to place your compost cup is important. Bacteria and fungi LOVE to a warm environment. So placing the cup in the sun warms the organic material, which promotes increased microbial activity. You want your compost to stay moist, so some shade is good too. The shade keeps the compost from becoming too warm, which could cause your compost to dry out.

Composting needs oxygen, heat, and water to be successful. These three elements help the microorganisms to multiply and survive. Your compost cup is ready and the composting process is underway! Keep the soil moist by adding water, shake it up occasionally and let nature do its thing for about 3 weeks.

Week 1: After about one week of decomposition, you will notice that the layers have lessened in size.

Week 2: The soil should have compacted more. If not, make sure the cup is getting enough sun. There should be water droplets visible on the inside. Make sure to keep the compost moist throughout the process. After about 3 weeks, dump out the contents and examine the soil.

What do you see in the soil?

Can you identify any of the materials placed in the cup three weeks ago? While composting is a great way to reduce the amount of food waste sent to local landfills, it can only be used with organic food waste. Composting alone will not eliminate all food waste in the United States, however, it will help our planet by reducing methane gas emissions and lessen the number of materials sent to landfills. Ultimately, composting is a great way to create a healthier world while also decreasing our carbon footprint.

Green kids, the earth is depending on you to brainstorm other ways to help reduce landfill waste! Think about ways to “reduce, reuse, and recycle” some of the items that end up in the trash can after a whole day of eating and snacking, including the packaging.