Making a Mold Terrarium

Mold growing in Petri dishes.

Mold is that fuzzy stuff growing on the food in your refrigerator. Making a mold terrarium is a fun way to teach children about things that don’t grow from seeds (molds grow from spores), what happens to food when it is left too long uneaten; not all mold looks the same or grows the same. Mold, in nature, is a useful thing. It helps food rot—in a natural environment this helps it to turn back into the soil, providing nutrients for other plants. It’s a natural recycler.


  • A clear container with a lid (big glass jars and clear plastic containers work well. You’ll throw the container away when you’re through.)
  • Adhesive or duct tape
  • Water
  • Leftover food such as bread, fruit, vegetables, cheese, cookies or cake. Do not use meat of any kind. It will begin to smell after a few days! 


  • Cut the food up into small pieces—1-inch chunks will do.
  • Dip each piece into some water and put it into your container. If you are using a big jar lay it on its side and try to spread the pieces out so they are not all in a heap.
  • Put the lid on the container and tape around the edge of the lid to seal it.
  • Put the container in a place where no one will knock it over or throw it away. Label it Mold Terrarium.
  • Look at the food each day. After a few days you’ll begin to see blue, green, or white fuzzy stuff growing on some of the pieces of food.
  • After a few more days things will start to rot and look really gross. Watch how the mold spreads and how things rot for about two weeks. Not much will happen after that.


  • What food started getting moldy first?
  • What color is the mold? How many different colors do you see?
  • What texture is the mold—flat, fuzzy, bumpy?
  • Does everything get moldy?
  • Does mold spread from one piece of food to another?
  • Do different kinds of mold grow on different types of food?

When you are through with your mold terrarium, throw it in the garbage. Do not reuse the container! Many people are allergic to molds so do not open the container!

This article was contributed by Mary Perkins for the February 2021 Early Childhood Express. This post is adapted from The Science Explorer.