- You don't have to purchase a special container to make your own terrarium. Any container made with clear plastic or glass works well. Uncovered containers will work, but require watering often. Stay away from colored or cloudy glass because the lighting is reduced. Find a container with a transparent cover or a small opening to maintain high humidity. Purchase a high-quality potting soil to ensure a sterile, well-drained and organic growing medium. You can mix your own, but it must be sterilized first.
- Plants that are slow-growing, low-growing and dense grow best in terrariums, but other plants work well. Select plants that grow in highly humid conditions and low lighting over plants, such as cacti or succulents that grow best in open dish gardens. Pick plants with a mixture of colors, textures and sizes, but always use plants with similar light, temperature and moisture requirements. Decide the site for the terrarium and select plants suited for the temperature and light provided.
- Clean, sterilize and dry the container. Use either water and bleach at a ratio of 15 to 1 or hot, soapy water and then rinse several times. Do not use a glass cleaner, as this requires several days to air out. Place the terrarium in the location selected, but never in direct sunlight. Determine the basic layout by evaluating the size of the container, number of plants included and how many sides are viewable. Create a drawing or set the plants up in a site with the same dimensions.
- Cover the bottom with 1 to 3 inches of gravel for drainage. Add a 1/2-inch layer of charcoal to eliminate toxins. Place sphagnum moss over the charcoal to keep the soil from reaching the gravel layer. Add at least 1 1/2 inches of potting soil. Remove the plants from the containers. Trim off any frail foliage and prune encircling roots before planting them in the terrarium at the same depth. Mist the plants for two days and then wait until the foliage dries before covering.