Science project

Compost Ingredients


  • 6 sealable plastic bags (sandwich size)
  • 6 plastic straws
  • Masking tape and pen for labeling
  • Digital instant-read thermometer
  • Tape
  • Scissors
  • Lettuce
  • Newspaper
  • Kitchen scale
  • Water
  • Measuring spoons


  1. First, set up your bags. These bags are your compost cookers. Using a pen and masking tape, label each bag with a number from one to six.
  2. It’s easier for materials to compost when they’re smaller, so get chopping. Tear the lettuce into small pieces no more than an inch wide. This is your green material. Use the scissors to chop up the newspaper into pieces that are roughly the same size as the lettuce. This is your brown material.
  3. Get a large straw and slip it around the base of the digital thermometer.  Make sure that it fits.
  4. Now it’s time to create your compost mixtures. Using a kitchen scale, weigh the following amounts for the different bags:
  • Bag 1: 0 oz newspaper, 0 oz lettuce. This is your control bag.
  • Bag 2: 8 oz newspaper
  • Bag 3: 8 oz lettuce
  • Bag 4: 2 oz newspaper, 6 oz lettuce
  • Bag 5: 4 oz lettuce, 4 oz newspaper
  • Bag 6: 6 oz newspaper, 2 oz lettuce

Compost Setup

  1. Now, place the materials into the bags. In each bag, place a tablespoon of water. Then slide a straw into the middle of the bag before you close it up. Seal the bag around the straw, and close it up with tape so it doesn’t open. Place all of the bags in a well-ventilated area that does not get direct sunlight.
  2. Create your hypothesis, your best guess about what’s going to happen. Which bag will start to compost first?
  3. Over the next few days, measure the temperature inside each bag. Slide the thermometer into the straw to do the test. Don’t open the bag, since it’s likely getting goopy and moldy in there!
  4. Put the temperatures into a chart.
  5. Do the temperatures in the bags change? Are the temperatures in bag 1 the same as those in the other bags, or are they all different? Why?


Within a few days, things will get cooking and you’ll begin to see results. In part, your results will change depending on where you keep your compost experiment: a cold basement is more like a fridge, and it will keep your compost colder.

In general, composting mixtures that contain half green materials and half brown materials tend to compost most quickly. Is this what you discovered?


Composting seems like it’s simply a matter to putting rotting bits of vegetables into a bin, but it’s much more than that. Composting turns organic materials like green vegetables, uneaten fruit, and dried leaves into beautiful soil. How does this happen?

To compost, you need a few different ingredients. First, you need green and brown material. Green material contains nitrogen, something that plants need to grow. Your greens are the fresh things that you put into your bin, like old lettuce or a rotten pear.

Next, you need some brown materials. These are rich in carbon. Brown materials include things like dried leaves or pieces of newspaper.

The next ingredient is nearly invisible. If you turn over an outdoor compost, you’ll discover many worms and other invertebrates (bugs) that are munching their way through your compost, turning it into rich soil. Other smaller organisms are doing the same thing. Fungi help turn compost materials into soil, and so do tiny microorganisms that you can’t even see with your eyes.  All of these creatures help composting happen.

Green and brown materials are the two big pieces of your recipe, but you need more. Water helps the composting organisms survive. However, too much water means that there’s not enough space for air, and those little critters aren’t happy. This leads to stinky compost.

As you can see, composting is a balance between many different things. In your bags, you placed green materials (the lettuce) and brown materials (the paper). You also put microorganisms in there, even though you couldn’t see them. They are on those ingredients, and they’re even in the air around you! Finally, you added some water to make sure the creatures in your compost were happy.

When compost begins to heat up, this means that the compost is turning into soil. When the tiny creatures in the compost start to take apart the big pieces of compost and turn them into something else, this process releases heat. Heat is a sign that your compost is working.

There are many ways that you can experiment with different composting recipes. Experiment with different amounts of moisture and air in the bags. Does this change how quickly your compost gets warm?  Try different sorts of fruits and vegetables, including pesticide-free fruits and vegetables. Does this make a difference?

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