A well-designed terrarium produces a miniature world that creates its own climate. Oklahoma State University's fact sheet on terrariums recommends using commercial potting medium in a terrarium without sand, rocks or charcoal. A sterile growing medium nurtures the plant roots and distributes moisture. The plants recycle the moisture they take in through the roots and transpire it--releasing the moisture into the atmosphere through their pores. This creates a rain forest effect in a covered terrarium. The warm, moist atmosphere provides a comfortable environment for tropical plants and other plants that thrive in a protective, moist environment.
Wash the container with dish soap and rinse twice to clean away all the soap. Polish the container with a dishtowel.
Pour 2 to 3 inches of potting mix into the container.
Mist the potting mix to moisten it.
Form a miniature landscape with your hands or a long-handled spoon. Create a hill toward the back and a valley near the front to vary the terrarium's terrain.
Dig holes for the plants with a spoon or miniature shovel. Space the holes 3 to 5 inches apart to allow growing room. Avoid planting plants right next to the glass.
Plant the tallest plants near the center and towards the back of the terrarium.
Plant medium-size plants between the glass and the terrarium's center.
Plant low plants such as mosses and creepers in the front and around the sides.
Mist the plants. Avoid over-watering. Make the soil damp and refrain from saturating the soil. Too much water will rot the plant roots.
Add a pathway of sand or miniature gravel between the plants. A curving pathway through the valley in the front of the terrarium adds interest to the landscape.
Place figures in the terrarium if desired, such as people fishing or forest animals. Use kitchen tongs to place figures in deep containers or containers with small openings.