Terrariums 101: Making a Garden Under Glass

Terrariums are defined as any sealed container that has soil, water, and plants inside of it. Most terrarium vessels are clear glass and have a lid that can be removed for maintenance and cleaning. While modern terrariums come in many shapes and sizes, the idea behind growing plants in portable containers has been around since the early nineteenth century.

British physician and avid botanist, Dr. Nathanial Ward, is credited with discovering and transporting plants on ships using his creative invention, the Wardian case. Dr. Ward was keeping moth cocoons in small sealed jars when he noticed that a fern had started to grow on a small piece of soil. His observation was that the fern was growing nicely without any additional care and this in turn led to a breakthrough in plant transportation that brought many new plants from around the world back to Europe. After 1829, the Wardian cases were used extensively to transport living plant materials on journeys across the seas. The cases protected the plants from salt spray and kept the plants moist and warm for the duration of their journey.

Wardian cases reached the height of fashionable interior design in early London as they protected sensitive plants from the surrounding air pollution created by the dependence on coal for heating. Many fashionable drawing rooms around London had a Wardian case filled with mostly ferns and prized orchids. Terrariums come and go in today’s popular culture, but their history shows that inventive minds can populate the world with rare plants through simple observation. Almost any glass container can be planted as a terrarium as long as it can be sealed. Anything from pickle jars, to old bottles, to fish bowls, and even aquariums can be used. 

Terrarium gardening is an interesting way to illustrate how ecosystems and the water cycle works. Water introduced into the terrarium vessel is absorbed through the plants roots by osmosis and transported up through the xylem and out of the plant through small holes in the plants leaves called stomata. The water is then transformed into vapor and released into the atmosphere in a process called transpiration. Water in the terrariums atmosphere then condenses on the top of the vessel and ultimately rolls down the sides and back into the soil where the plants roots absorb the water thus completing the water cycle. This process makes terrariums self-nourishing and they require very little care if managed properly

Tips for managing terrariums:

  • Terrariums prefer bright light but not direct sunlight. A sunny window is the perfect location, but be sure to check that the outside of the glass is not getting hot to the touch as this is an indicator that the area may not be suitable. Move the terrarium to a location that has bright light such as an east or south facing window.
  • When watering the terrarium only add small amounts of water at one time. Water can be easily added to the vessel, but removal can be difficult. Try using a spray bottle by misting the soil gently. Only water when the sides of the vessel stay dry for over one week as this is a sign that water needs to be added to the cycle.
  • If the vessel becomes cloudy, the lid can be removed to allow the terrarium to dry.
  • Fertilization is not recommended, as the plants will quickly out grow their small home.
  • When creating a new terrarium try to keep the insides of the glass as clean as possible and do a thorough cleaning before adding any components.
  • Plant leaves that touch the sides or top of the glass should be trimmed back from the glass to prevent molding and algae growth.
  • Over time, it may be necessary to empty your terrarium and create a new one. Try plants similar to ones that have worked in the past.
  • Succulent plants should only be planted in an open top container or dish.

-Lance Swearengin, horticultural curator

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