2. Fill the bottom half in layers: 1 inch of pea gravel, 1â„2 inch of activated charcoal (find it at pet stores), and the rest with damp potting soil. Insert plants (we used wood fern, strawberry begonia, and asparagus fern) and plastic toys into the soil.
3. Secure the top of the bottle to the bottom with washi tape. Place a small bouncy ball onto the spout opening to seal it (hot-glue in place, if desired). Set the terrarium in a bright area, not in direct sunlight, and watch it grow!
The LessonIn the terrarium, water moves from the soil into the plant, out to the air, and back down again in a process called the water cycle. Here's how it works:
Transpiration: Moisture is carried from the soil through the plants' roots to small pores on the leaves.
Evaporation: The tiny drops of water transform from a liquid to a gas, leaving as a vapor from the plant.
Condensation: The water vapor can't get out of the closed terrarium, so it collects on the inside of the bottle and turns from a gas back into a liquid.
Precipitation: When a lot of condensation forms, it gets too heavy to stick to the bottle. It slides down the sides, just like rain or snow falling from a cloud. The plants soak up the precipitation through their roots, and the process starts over again.