June 2017 Terrarium

Garden in a Glass (6/7/17)

Building a Sealed Terrarium


  • Glass Jar with a lid
  • Small rocks (river pebbles, aquarium stones, or even colorful glass beads will work!)
  • Wire cloth (fine mesh window screen material is perfect)
  • Activated Charcoal
  • Peat Moss
  • Potting Soil
  • Moss, Small Plants, Seeds, or whatever else you want to grow in your terrarium
  • Spray Bottle filled with purified water
  • Some pretty accent rocks, or small plastic figurine for decoration


  1. First, we need to choose a suitable jar for our terrarium. A tall bottle with a narrow opening can be a good choice when planting taller plants, but jars with a wider mouth will be much easier to work with. You could even use a cleaned peanut butter jar!
  2. Scoop enough small rocks into the jar to create a layer about 1 inch deep. These stones will provide drainage space for extra water to collect in.
  3. Cut a piece of wire cloth to cover the layer of rocks in your jar. This wire cloth should allow water to pass through it, but also keep dirt from settling to the bottom.
  4. Cover the wire cloth with a thin layer of activated charcoal. You can usually buy activated charcoal at pet stores because it is used to filter aquarium water, just as it will filter the water in our sealed terrarium.
  5. Add a ½ inch layer of peat moss, followed by a 1 inch layer of potting soil. The peat moss will provide nutrients for our growing plants, and the potting soil will create a stable foundation for the plant roots to grow in.
  6. Now it‘s time to add the greenery! Carefully plant whatever small plants you would like to grow in your terrarium, keeping in mind that each plant will need plenty of room to grow. Do not overcrowd them! For a smaller jar, you may want to only grow a single plant. For larger jars, you could add two or more. You could also add a few plant seeds to your terrarium, if you’d like to watch your plants grow from scratch (be sure to follow any planting instructions on the back of the seed packet).
  7. You can also add moss to your terrarium by harvesting small chunks of moss (with a bit of dirt still attached to its roots), and simply tapping it down into the surface of the potting soil.
  8. Using a spray bottle, add enough water to thoroughly dampen the surface of the soil. You can also use the spray bottle to clean away any dirt that is sticking to the inside of the jar or to leaves of the plant. Be careful to not over-water your terrarium! Once you see some water dripping into the rock layer, stop watering!!
  9. Finalize your terrarium landscape by adding a decorative rock or two, a plastic animal figurine, a tiny garden gnome, or anything else that looks cool next to your plants.
  10. Tightly seal your terrarium and place it in a safe spot. Some plants like to have direct sunlight, while other plants prefer to grow in partial shade. However, most plants will grow well when placed near a sunny window.
  11. Observe any changes in your terrarium over the next few days. Do you notice water droplets forming on the inside of the jar? Where do you think this water has come from? (The droplets should form only in the morning and again in the evening—but if the droplets are present all day long, you should open the terrarium for a few hours to let extra water evaporate out. If you do not see droplets on the glass, or your plant is beginning to wilt, you may want to add a bit more water.)
  12. You should only open your terrarium if your plants look extremely dry and need another watering. Otherwise, just sit back and watch your plants grow for months or even years to come!
Terrarium layers


Sealed terrariums are an easy and fun way to create a self-sustaining garden in a very small space. Plants can survive for a long time in a sealed terrarium after just a single watering due to a special process called the Water Cycle.

Water in the pebble layer at the bottom of the jar will evaporate, or turn from liquid water into vapor, and humidify the air within the jar. Some of this water vapor will cling onto the walls of the jar, creating tiny droplets of liquid water—a step called condensation. As the droplets grow larger and heavier, they will eventually “rain down” onto the plant and soil below in a step called precipitation. This water could be taken in by the plant’s roots, or simply drip back to the pebble bottom and start the cycle all over again. Water that is taken in by the plant is still part of the Water Cycle, because the plant will release this water back into the air in a step called transpiration. Transpiration is a lot like sweating, but for plants! Plants release water into the air through special pores (or openings) in the underside of the leaves.

Terrarium water cycle

The Water Cycle allows the water inside your terrarium to continuously hydrate your plants almost indefinitely, but what about the plants outside of a terrarium? How does the Water Cycle affect outdoor plants like grass and trees? Can you identify how water is recycled in nature?

In addition to water, plants need certain nutrients like carbon, phosphorus, and nitrogen in order to grow strong and healthy. In our sealed terrariums, plants must recycle these important nutrients that are initially provided in the peat moss and potting soil. As older leaves fall off the plant, they will begin to rot and decompose, or break apart, releasing nutrients back into the soil to be reused by the plant.


Sealed terrariums can keep plants growing for a long time without having to add more water. Incredibly, one such terrarium has been growing for almost 60 years!

In 1960, David Latimer planted a Spiderwort plant inside of a 10-gallon glass container terrarium. It wasn’t until 1972 (twelve years later) that he decided to open the container to add some extra water for the growing plant. He hasn’t needed to open it since then! You can read all about David’s long-lasting terrarium online.

Terrarium giant

Time to get growing!