It’s fun and easy to make your own small ecosystem in a bottle—a terrarium.

Begin with a clear container that has a lid, such as a two-liter soft drink bottle or a glass jar. Soak the container in warm water if necessary to remove the label.

Gather pebbles from near your home or buy some at a gardening store. Rinse the stones, then lay them on the bottom of your container. A one-inch (three-centimeter) thick layer should be plenty. If the neck of your bottle is narrow, you can make a funnel by rolling a piece of paper. Then drop the stones through the funnel.

Add a layer of potting soil, which you can also get at a gardening store. This layer should be two or three inches (five to eight centimeters) deep. Soil from your yard or garden might also work, but terrarium soil needs to be extremely fertile, so potting soil is your best bet. Adding a little ground charcoal to your soil will make it richer still and better for growing plants.

Now find plants to grow in your terrarium. Mosses and lichens from the woods work well. So do ferns, small flowering plants, and ivy shoots, which you can pinch right off a growing ivy plant. (Be sure to get permission before taking anyone else’s plants.) Make small holes for plant roots in your soil with a stick, then position your seedlings. Cover the roots with a little soil. If the neck of your container is narrow, you can use two long sticks pinched together chopstick style to position your plants.

Add enough water to dampen the soil. Punch small holes in the lid. Air can get in, but most of the water gets recycled in the container rather than evaporating away. Put the lid on the container and place it somewhere that gets lots of light—but not direct sunlight, which would overheat the plants growing inside. Add water occasionally if your terrarium gets dry. And watch your miniature ecosystem come to life!