A kid-sized rainforest biome suitable for home or classroom use may be created using a covered aquarium, gravel, charcoal, potting soil, tropical plants and water. Combined, these items create the moist, humid conditions of a tropical rainforest, similar to those found in Brazil or Costa Rica.
When used for miniature gardens, an aquarium is called a terrarium. Start by putting some gravel at the bottom of the large fish tank, followed by some charcoal, the type used for plants, such as orchids. Cover this with about 1 inch of rich potting soil, available from a nursery, or compost from a garden. Moisten the soil just enough to make it damp.
Add the plants. Use varieties that grow well in warm, moist conditions. Suggestions include spider ferns, air plants or moss. After planting, use a spray bottle to moisten the plants, then put a clear glass lid over the top of the terrarium. The glass must be clear to let in sunlight. Place the aquarium in a warm, sunlit spot.
After a few hours, the heat from the sun causes the evaporation of some of the water in the terrarium. Instead of being released into the air, the water droplets form on the tops and sides of the terrarium, creating humidity. The drops eventually get large enough to fall back on the plants and soil, just like rain does in a real rainforest.