A terrarium is an enclosed growing environment that creates its own miniature ecosystem. You can use nearly any type of clear container to create a terrarium, as long as it's watertight, has a lid or cover and is large enough for the plants that will grow in it. The best types of plants to grow in a terrarium are slow-growing and reach only a small size at maturity. The plants should also have the same or similar light and moisture requirements. Some good plants for growing in terrariums are small ferns, mosses, creeping figs, Buddhist pines (Podocarpus), nerve plants (Fittonia), aluminum plants (Pilea), Ardisia and miniature African violets.
Wash and dry the clear plastic or glass container thoroughly. Spread a ½-inch layer of pea gravel on the bottom of the container.
Place a 4-to-5 inch layer of lightweight, all-purpose potting soil on top of the pea gravel. Add more soil, as needed, if the plants you've chosen have deeper root systems.
Design the plant arrangement in your terrarium before planting. Place the taller plants in the background and the smaller ones in the foreground.
Dig a small hole into the potting soil surface using your fingers for each terrarium plant. Place each plant's roots into the planting holes and cover the roots with the soil.
Water the terrarium soil and plants lightly to moisten the potting soil. Place the lid or cover on the container and position the terrarium in a medium-light area, away from direct sunlight.
Pinch back the plants to control their height when they begin to grow too tall for the container. Water the terrarium once every three weeks, only when the soil begins to dry out and there's little to no condensation on the inside of the container.