Linda Geist

COLUMBIA, Mo. – Terrariums are back in style for plant lovers, says University of Missouri Extension horticulturist David Trinklein.

Transparent plant containers date back at least 2,500 years, but the modern terrarium is a more recent innovation. Nineteenth-century London physician N.B. Ward had an interest in insects. When studying a sphinx moth emerging from a chrysalis he had buried in moist earth in a closed bottle, he noticed a seedling fern and grass growing inside. He watched the plants grow in this closed environment for four years, without adding water or removing the cover. Thus was born the modern terrarium.

“Terrariums are an interesting way to grow a small number of plants in a home that might be too hot or the air too dry for growing most plants,” Trinklein said.

There are two types of terrariums: closed and open, he said. Closed terrariums are more traditional and retain more humidity than open ones, though open terrariums still provide higher humidity for plants than dish gardens, in which plants are grown in a shallow container. Open terrariums and dish gardens require more frequent watering, but danger of disease outbreak is reduced.

To make a home terrarium, choose a clear glass or plastic container: empty fishbowls, fish tanks, brandy snifters, old glass jars, jugs, bottles, etc.

Use a porous growing medium that drains well and is high in organic matter and free from disease organisms. Prepackaged peat-like mixes make excellent choices.

Choose plants with a low and dense growth habit, Trinklein said. Don’t mix plants that have widely different light and temperature requirements.

Place plants that need medium light in good light near a window or an artificial light source. Put plants that tolerate low light no more than 10 feet from a bright window.

Most terrarium plants are tropical in nature and require a warm, but not hot, environment, Trinklein says. A night temperature of 65 F is ideal for this type of plant; day temperatures normally should be about 10 degrees higher. A few terrarium plants prefer cooler conditions and should have night temperatures of about 50 to 55 degrees.

Growing medium and drainage material should fill about one fourth of the terrarium. Place charcoal and pebbles in the bottom of the container below the growing medium for drainage. Charcoal helps eliminate potentially toxic byproducts in closed terrariums.

When planting a terrarium, take plants from their pots and remove extra growing medium to expose the roots. Trim off yellowed or damaged leaves that show any sign of disease or insect damage. If plants are extremely pot-bound, trim off some roots to encourage new root growth. Promptly place the plant in the container. Do not allow exposed roots to dry. In the closed container, try to keep foliage from touching the sides of the container. Leaves that touch the glass may collect water and are more likely to rot.

After planting, mist over the plants to wash off any growing medium that sticks to leaves or sides of the container. Water misted over the leaves is adequate to settle the medium. Repeat the misting after one day. Allow the container to remain open until the foliage has thoroughly dried. Then, if the terrarium is the closed type, apply the cover. Watch the newly planted terrarium closely for several weeks for signs of disease or other problems.

Plants in terrariums should not grow rapidly and seldom need fertilizer, Trinklein said. Don’t plan any fertilization for at least a year after planting.

To learn more, see the MU Extension publication Terrariums (G6520).

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