A terrarium is a container for gardening that is constructed mainly of glass. Terrariums are like little greenhouses, in that they allow the light to build heat for the plants inside. The design of terrariums are more elaborate than a basic greenhouses and come in a variety of styles, from Victorian styles (where they were immensely popular) to hanging to modern. Terrariums do not usually have drainage, so keep that in mind when purchasing. If the lid remains closed, moisture will gather as in a greenhouse, and the lid will need to be opened on occasion to allow condensation to evaporate, and maintain your plants.