News release: Terrariums, Part I

Tim Baker, MU Extension Professional Field Specialist in Horticulture
102 N. Main, Suite 1, Gallatin, MO 64640

Release Date: January 17, 2019
Headline: Terrariums, Part I

An interesting aspect of plant science is the study of plant growth requirements.  These experiments have often taken place within isolated growth chambers, where temperature, light, water, nutrients, and other environmental factors are carefully controlled.  These expensive chambers are fascinating, because they attempt to emulate the plant's natural environment artificially.  All the factors needed for growth are provided in a setting that is isolated from its surroundings.

Of course, growth chambers are well beyond the financial resources of most plant hobbyists.  However, if you like the idea of experimenting with an isolated, controlled environment for plants, terrariums provide an interesting alternative.  A terrarium consists of a closed glass or plastic container that contains small plants.  Soil and plants are placed in the container, watered, and then sealed by placing a glass or plastic cover over the container.  The plants are therefore isolated from their surroundings, and only require a little water and fertilizer infrequently.

While using transparent containers for plant growth has been with us since the Greeks, the modern techniques were developed in the 1800s by Dr. N.B. Ward in London.  Dr. Ward found that a seedling fern and grass growing inside a closed bottle grew well for four years without adding any water or removing the cover.  He published his findings in 1842 in a book titled “On the Growth of Plants in Closely Glazed Cases”.  This led to the development of the "Wardian case," which became popular in the Victorian era.

Containers for terrariums should be clear, for optimum light transmission.  Almost any type of container is acceptable, including old fish tanks, bottles, jugs, or glass jars.  You will need some type of transparent cover if you want to have an isolated system.  You may, of course optionally have an open container, but this will require more frequent care.  The choice of closed vs. open containers will be somewhat dictated by the type of plant you want to grow.

To prepare your terrarium, start with some sterile gravel to be placed on the bottom.  It is important that all ingredients (except the plants) be sterilized before being placed in the container.  The closed container has many advantages, including the exclusion of diseases and insects.  However, if pathogens or insects are introduced by mistake, the closed container will work against you, since the conditions are ideal for their spread.  Next, you will need a sterile soil mix.  Commercial soil mixes high in peat moss are good.  You may also prepare your own mix, sterilizing it before use.

In my next column, I will discuss selection of plants and other factors that go into making a successful terrarium.