Terrariums are great for plants that require moist, humid environments. Succulents don't usually prefer these types of conditions. Because succulents use their thick, fleshy leaves and stems to hold water, they don't need moist, humid conditions. Traditional closed terrariums hold in moisture and humidity. These wet environments will rot and kill succulents in very little time. In order to successfully marry the two, you'll need to make a few easy tweaks to the traditional terrarium.