1. Select plants for your terrarium. Dwarf and slow-growing plants that thrive in warm, moist air work best. Plants with different heights, shapes and textures add interest.
2. Gather ornamental accessories. Small pebbles can resemble rocks and boulders; small branches and moss give your garden a natural look.
3. Choose a clear container large enough to hold the plants you want to enclose. Wash it thoroughly.
4. Put down a layer of drainage material, such as pea gravel. Depending on the size of your container, you'll need about a half-inch to 3 inches of pea gravel.
5. Sprinkle with fine charcoal (generally available at garden centers), which absorbs gasses and chemicals.
6. Layer 2 to 6 inches of a sterile peat-based potting mix over the base.
7. Gently tap plants out of their pots. Trim rampant roots to encourage plants to grow more slowly and to more easily fit into the shallow, restricted root zone in the container.
8. Place plants in holes and press soil gently around the roots. Use long-handled tools if necessary to avoid damaging other plants. Start in the middle and work outward.
9. Add finishing touches such as moss and rocks.
10. Mist with water to settle the roots and clean the plant. The soil should be moist but not soggy. Cover your terrarium. (You can also leave your terrarium open, but it will need more frequent misting.)
Caring for your terrarium
Light: Put your terrarium where it will get enough light to satisfy the plants' needs, but keep it out of direct sun, which will overheat the garden.
Water: Check moisture levels periodically, and mist if your terrarium needs water. Plants should not dry out, but they also shouldn't be overwatered. If spots of mold or mildew appear, your garden has too much moisture; remove or partially open the lid for two or three days to improve air circulation.
Pruning: Prune plants to keep them from overgrowing their neighbors. Remove dead plants and plant parts as they appear.