Mold Terrarium

  One Hour or more
What do I need?
Kids Looking at Terrarium


  • A clear container with a lid. (Big glass jars and clear plastic containers work great, but you'll have to throw away the container when you're through, so check with a grown-up about what you can use.)
  • Adhesive tape
  • Water
  • Some leftover food (you can use whatever is in your refrigerator), such as bread, fruit (like oranges, lemons, or grapes), vegetables (like broccoli, zucchini, or green pepper), cheese, and cookies or cake


This Is Important!

DO NOT use anything with meat or fish in it—after a few days, these foods would start to smell very, very bad.

1 Ask a grown-up for four or five different pieces of leftover food. If the food is small—a grape or one section of an orange—use the whole thing. Cut bigger foods such as bread or cheese into 1-inch chunks.

  Girl making terrarium

2 Dip each piece of food into some water and put it into your container. If you use a big jar, lay it on its side. Try to spread the pieces out so that they are close to each other, but not all in a heap.


3 Put the lid on the container. Tape around the edge of the lid to seal it.

4 Put the container in a place where no one will knock it over or throw it away. You may want to label it "Mold Terrarium."

5 Every day, look at the food in your Mold Terrarium. For the first two or three days, you probably won't see much. But soon you should see blue or green or white fuzzy stuff growing on some of the pieces of food.

6 After a few more days, some of the food in your mold terrarium may start to rot and look really gross. You can watch how the mold spreads and how things rot for about two weeks. After that, it'll get boring, because not much more will happen.

  Moldy food!

When most foods get moldy, it means they aren't good to eat any more. But some cheeses are eaten only after they become moldy! Blue cheese gets its flavor from the veins of blue-green mold in it. When a blue cheese is formed into a wheel, holes are poked through it with thin skewers. Air gets into these holes, and a very special kind of mold grows there as the cheese ripens.



   Here are some things to notice in your mold terrarium:

  • 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 in your Mold Terrarium 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're through with your Mold Terrarium, throw it in the garbage. Don't reuse the container. Don't even open the lid! Mold is not a good thing for some people to smell or breathe.

What's going on?

What is mold, anyway?

That fuzzy stuff growing on the food in your mold terrarium is mold, a kind of fungus. Mushrooms are one kind of fungus; molds are another.

Unlike plants, molds don't grow from seeds. They grow from tiny spores that float around in the air. When some of these spores fall onto a piece of damp food or other materials, they grow into molds.

Plants contain a chemical compound called chlorophyll. Chlorophyll makes it possible for plants to capture the energy of sunlight and use it to make food (sugars and starches) from air and water. Unlike plants, molds and other fungi have no chlorophyll and can't make their own food. The molds that grow in your mold terrarium feed on the bread, cheese, and other foods. A mold produces chemicals that make the food break down and start to rot. As the food is broken down into small, simple parts, the mold absorbs them and grows.

Ick! Who wants this stuff around?

It can be annoying to find moldy food in your refrigerator. But in nature, mold is a very useful thing. Mold helps food and other materials rot, which is an icky but necessary thing. In a natural environment, rotting things return to the soil, providing nutrients for other living things. Mold is a natural recycler.

Why does the mold on different foods look different?

There are thousands of different kinds of molds. One mold that grows on lemons looks like a blue-green powder. A mold that grows on strawberries is a grayish-white fuzz. A common mold that grows on bread looks like white cottony fuzz at first. If you watch that mold for a few days, it will turn black. The tiny black dots are its spores, which can grow to produce more mold.

Why didn't some foods get moldy?

If you used foods that contain preservatives, mold may not have grown very well on them. If you want to experiment more with mold, you can make one mold terrarium using food with preservatives (like a packaged cupcake) and another using food that doesn't have preservatives (like a slice of homemade cake). Which one grows more mold? You can also experiment with natural preservatives such as vinegar and salt. If you do more experimenting, let us know what you discover!

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About the Books

Published by Owl Books,
Henry Holt & Company, New York,
1996 & 1997

ISBN 0-B050-4536 & ISBN 0-8050-4537-6 ,
$12.95 each

© 1998 Exploratorium