A terrarium is a miniature indoor garden built inside a clear glass or plastic container. Think of it as a tiny world under glass: you layer soil, rocks, and charcoal at the bottom, then add small plants like ferns, moss, or succulents. The transparent walls let you watch your plants grow while keeping them protected.

Terrariums work like small greenhouses. When you water the plants, moisture evaporates, condenses on the glass walls, and drips back down to the soil, creating a self-sustaining cycle. Some terrariums have lids, trapping moisture inside so you barely need to water them at all. Others stay open to the air, which works better for plants that prefer drier conditions.

People create terrariums in mason jars, fish tanks, light bulbs, or any clear container. Building one teaches you about ecosystems in miniature: how plants, water, soil, and air all work together to sustain life.