Tam-Tam's Blog

Terrariums...figuring out how it works.
Dec 12, 2007 | 8:28 PM PST
Tags: Terrarium , Photosynthesis , Respiration , Rain cycle

If you think about the processes that take place during a plant's life, you can get an idea as to why this little glass case would work so well.  The processes of Photosynthesis and Respiration, the refresher course: 
Photosynthesis goes on in the presence of light, sunlight or the use of special growing lights for plants.  It occurs in the green cells only and uses carbon dioxide and water, releases oxygen and the plants increase in weight and store food. 
Respiration goes on all the time, in the light and in the dark, it occurs in every living cell of the plant, uses food and oxygen, releases water and carbon dioxide, and the plant decreases in weight.   These two processes are interdependent, they happen at the same time.  The material created by one process makes the other process possible.  So these two processes is how the plant uses the energy of the sun to make their own food called plant sugars---from carbon dioxide in the air and from water in the soil.  Some of these sugars are used as soon as they are made, while other amounts of the plant sugars are store in the leaves and stems and they are converted to food as the plant grows.  

So how does the terrarium work?  Basically it encapsulates the proper growing conditions.  For instance, the high humidity that numerous plants need is maintained constantly in the sealed terrarium.  It blocks off drafts and protects from excessive heat or cold, if positioned properly.  The "sunlight" provided by the lighting system can be optimal for the process of photosynthesis.  One key factor is moisture.  Moisture has to be introduced into the terrarium, because it is a self contained unit.  Once this has occurred, the process of photosynthesis can begin but this also produces the process of the rain cycle.  

In the rain cycle, the water that is absorbed by the plants roots are released as vapor through the leaves, the vapor evaporates into the air and eventually falls back into the dirt through the process of condensation.  As the moist vapors rising form the plants reaches the cooler glass, it condenses, dripping to the dirt like raindrops from the glass.  Because the water is again absorbed through the roots, this becomes a never-ending process.
Once the rain cycle has been established, the terrarium garden has a constant supply of moisture.  This means that the terrarium never has to be watered as long as condensation "fogs" the sides of the container.  The tight fitting lid or cover allows this rain cycle to happen constantly, but it also keeps the gases needed for photosynthesis and respiration from escaping.   

When thinking about terrariums two types come to mind--Tropical and Desert.  Several tropical plants prefer humidity, this makes it hard to keep these plants healthy in the dry heat we use for the winter.  This can make the terrarium a great idea for slow or low growing tropical plants.  On the other hand, desert plants like the dry air and the terrarium can make an ideal place for them to thrive.  Desert terrariums do not need the completely sealed covers.  In fact they need to have a supply of dry air to benefit their growing conditions.  Cacti and succulents make for a very interesting garden design.  When you set up a terrarium for animals, such as some type of small lizard, it becomes a Vivarium.

Next...the basics.  It's more simple than you might think.